Receiver circuit, related integrated circuit and apparatus

Abstract

A receiver circuit extracts data from a serial data signal. The serial data signal contains a data packet having a first format with a first number of bits or a second format with a second number of bits based on a selection signal. The second format comprises the bits of the first format followed by one or more additional bits. The receiver circuit has at least one shift register having a total number of bits equal or greater than the number of bits of the second format and a switching circuit that selectively connects the serial data signal to one of the shift register serial inputs as a function of the selection signal. When the first format is selected and the respective bits received, the bits are stored in given positions of the one or more shift registers. The switching circuit also, when the second format is selected and the respective bits received, stores the bits of the first format included at the beginning of the second format in the same given positions of the one or more shift registers.

Claims

1. A receiver circuit to extract data from a serial data signal, the serial data signal containing a data packet, wherein based on a selection signal said data packet has bits arranged in a first data packet format or bits arranged in a second data packet format, wherein said first data packet format has a first number of bits and said second data packet format has a second number of bits, wherein said second data packet format includes the bits of said first data packet format followed by one or more additional bits, said receiver circuit comprising: one or more shift registers having a total number of bits equal or greater than the second number of bits of said second data packet format, each of said one or more shift registers having at least one serial input; and a switching circuit associated with said one or more shift registers, said switching circuit configured to selectively couple said serial data signal to said at least one serial input of said one or more shift registers as a function of said selection signal, wherein: a) after said selection signal indicates that said first data packet format has been selected and after having received the bits of said first data packet format, the bits of said first data packet format are stored in given positions of said one or more shift registers, and b) after said selection signal indicates that said second data packet format has been selected and after having received the bits of said second data packet format, the bits of said first data packet format included in said second data packet format are stored in said given positions of said one or more shift registers.

2. The receiver circuit according to claim 1, wherein the one or more shift registers is a single shift register and wherein said switching circuit is configured to: a) when said selection signal indicates that said first data packet format has been selected, select a first input position of said single shift register to receive the bits of said serial data signal, and b) when said selection signal indicates that said second data packet format has been selected, select a second input position of said single shift register to receive the bits of said serial data signal, wherein said second input position corresponds to said first input position shifted by a number representing how many said one or more additional bits followed the bits of said first data packet format.

3. The receiver circuit according to claim 1, wherein the one or more shift registers includes a first shift register and a second shift register, and wherein said switching circuit is configured to: a) select an input position of said first shift register to receive a given number of bits of said serial data signal, and b) after having received said given number of bits, select an input position of said second shift register to receive further bits of said serial data signal.

4. The receiver circuit according to claim 3, wherein said given number of bits corresponds to said first number of bits of said first data packet format, such that the bits of said first data packet format are loaded into said first shift register and said additional bits are loaded into said second shift register.

5. The receiver circuit according to claim 3, wherein said given number of bits is smaller than said first number of bits of said first data packet format, and wherein said switching circuit is configured to: a) when said selection signal indicates that said first data packet format has been selected and after receiving said given number of bits, select a first input position of said second shift register to receive said further bits of said serial data signal, and b) when said selection signal indicates that said second data packet format has been selected and after receiving said given number of bits, select a second input position of said second shift register to receive the further bits of said serial data signal, wherein said second input position corresponds to said first input position shifted by a number representing how many said one or more additional bits followed the bits of said first data packet format.

6. The receiver circuit according to claim 1 wherein said first data packet format includes a given number of bits assigned to a data field and a given number of bits assigned to an address field, and wherein one or more of said additional bits are assigned to said address field, thereby increasing a total number of bits of said address field.

7. The receiver circuit according to claim 6, comprising: an address verification circuit configured to generate a signal indicating whether bits stored in said one or more shift registers and assigned with said address field correspond to one or more reference addresses.

8. The receiver circuit according to claim 1 wherein said first data packet format starts with a preamble having a given number of bits.

9. The receiver circuit according to claim 8, said receiver circuit comprising: a preamble verification circuit configured to generate a signal indicating whether bits stored in said one or more shift registers and assigned with said preamble correspond to a reference preamble.

10. The receiver circuit according to claim 1 wherein said first data packet format includes a given number of error checking bits having a computed value based on the bits of said data packet.

11. The receiver circuit according to claim 10, wherein one or more of said additional bits are additional error checking bits.

12. The receiver circuit according to claim 10, said receiver circuit comprising: an error checking circuit, the error checking circuit configured to: a) compute reference error checking bits based on bits stored in said one or more shift registers, and b) generate a signal indicating whether error checking bits stored in said one or more shift registers correspond to said reference error checking bits.

13. The receiver circuit according to claim 1, wherein said selection signal is determined as a function of the bits included in said first data packet format.

14. The receiver circuit according to claim 1, wherein said one or more shift registers and said switching circuit are formed in an integrated circuit.

15. An apparatus, comprising: a memory arranged to pass a selection signal, said selection signal arranged to identify whether a data packet has bits arranged in a first data packet format or bits arranged in a second data packet format, wherein said first data packet format has a first number of bits and said second data packet format has a second number of bits, wherein said second data packet format includes the bits of said first data packet format followed by one or more additional bits; a digital processing circuit to direct extraction of data from a serial data signal, the serial data signal containing the data packet; at least one shift register having a total number of bits equal or greater than the second number of bits of said second data packet format, each of said at least one shift register having a serial input; and a switching circuit associated with said at least one shift register, said switching circuit configured to selectively couple said serial data signal to said serial input of said at least one shift register as a function of said selection signal, wherein: a) after said selection signal indicates that said first data packet format has been selected and after having received the bits of said first data packet format, the bits of said first data packet format are stored in given positions of the at least one shift register, and b) after said selection signal indicates that said second data packet format has been selected and after having received the bits of said second data packet format, the bits of said first data packet format included in said second data packet format are stored in said given positions of said at least one shift register.

16. The apparatus according to claim 15, wherein said memory, said digital processing circuit, and said switching circuit are formed in an ultra-low power receiver circuit.

17. The apparatus according to claim 16, wherein said ultra-low power receiver circuit is formed in a multimedia device.

18. An method, comprising: passing a selection signal from a memory, said selection signal arranged to identify whether a data packet has bits arranged in a first data packet format or bits arranged in a second data packet format, wherein said first data packet format has a first number of bits and said second data packet format has a second number of bits, wherein said second data packet format includes the bits of said first data packet format followed by one or more additional bits; extracting, as directed by a digital processing circuit, data from a serial data signal, the serial data signal containing the data packet; selectively coupling with a switching circuit, as a function of said selection signal, said serial data signal to an input of at least one shift register, said at least one shift register having a total number of bits equal or greater than the second number of bits of said second data packet format; and a) after said selection signal indicates that said first data packet format has been selected and after having received the bits of said first data packet format, storing the bits of said first data packet format in given positions of the at least one shift register, or b) after said selection signal indicates that said second data packet format has been selected and after having received the bits of said second data packet format, storing the bits of said first data packet format included in said second data packet format in said given positions of said at least one shift register.

19. The method according to claim 18, wherein the at least one shift register includes a first shift register and a second shift register, the method further comprising: selecting an input position of said first shift register to receive a given number of bits of said serial data signal, and after receiving said given number of bits, selecting an input position of said second shift register to receive further bits of said serial data signal.

20. The method according to claim 19, wherein said given number of bits corresponds to said first number of bits of said first data packet format, such that the bits of said first data packet format are loaded into said first shift register and said additional bits are loaded into said second shift register.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Embodiments of the present disclosure will now be described with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:

(2) FIGS. 1, 2 and 3 show typical communication systems;

(3) FIGS. 4a to 4d show an exemplary a communication protocol;

(4) FIGS. 5a to 5d show first embodiments of a communication protocol in accordance with the present disclosure;

(5) FIGS. 6a to 6d show second embodiments of a communication protocol in accordance with the present disclosure;

(6) FIGS. 7a to 7d show third embodiments of a communication protocol in accordance with the present disclosure; and

(7) FIGS. 8, 9a-9d, 10a-10d, 11, 12, 13, 14, 15, 16, 17a-17c and 18 show various embodiments of receiver circuits in accordance with the present disclosure.

DETAILED DESCRIPTION

(8) In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or several specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments.

(9) Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

(10) The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

(11) FIGS. 1-3 illustrate embodiments of the present invention. In the following FIGS. 4 to 18, parts, elements, or components that have already been described with reference to FIGS. 1 to 3 are denoted by the same references previously used in such Figures; the description of such previously described elements will not be repeated in the following in order not to overburden the present detailed description.

(12) As mentioned in the foregoing, various embodiments of the present disclosure relate to solutions being suitable for ultra-low power communication, i.e., a system with near zero power consumption when being in stand-by mode. Accordingly, the solutions described herein may be used in a receiver circuit 22a to be used, e.g., in the apparatus 2 described in the foregoing. Possible applications include thus ultra-low power remote controlling, including RFID (Radio-Frequency IDentification) for smart home and smart building applications.

(13) As mentioned in the foregoing, a telecommunication protocol provides rules, including the syntax, semantics and synchronization of communication and possible error recovery methods that allow two or more entities of a communication system to communicate between them in order to transmit information via a variation of one or more physical quantities. There are many levels of protocols complexity able to manage the information exchanged between two devices (in wireless or cabled mode). The complexity is usually linked to the nature and amount of communication data which have to be transferred: this generates and characterizes the rules and conventions that can be set out to properly define the protocol itself. In a digital communication system, these rules are generically structured and packed with the final target to make them a portable language to be integrated in a custom design. Regardless of the complexity of the protocol, some basic properties are often used to establish a communication.

(14) FIGS. 4a to 4d show in this regards possible data packets for a serial communication protocol and FIG. 14 shows a possible embodiment of a respective receiver circuit 22a configured to determine the data DO transmitted over a wired or wireless communication channel by elaborating a received signal RX provided by a receiver 20, such as an IR or RF receiver, or any other receiver for wired or wireless communication. Accordingly, the data packet may be used for transmitting the data DI from the transmitter circuit 12 to the receiver circuit 22a.

(15) Generally, the receiver circuit 22a comprises a digital processing circuit 224 and has associated some kind of power supply, such as a battery and/or an electronic converter powered from the mains. For example, in the embodiment shown in FIG. 14, the receiver circuit 22a may have associated therewith a power control module or an energy harvesting circuit 26 configured to obtain the supply voltage VDD for the receiver circuit 22a from the communication channel, e.g., by extracting energy from an IR radiation or RF wave.

(16) In the embodiment considered, the strings of bits composing the digital message, i.e., the data packet, are divided into fields and each field carries relevant and well-defined information. Moreover, the various fields belong usually to a header HD or a payload PL. For example, the header HD usually contains the fields with more relevance for the protocol, i.e., the information required to transmit the data to a given receiver 22a, while the payload contains the data to be transmitted.

(17) For example, in the embodiment considered, the header HD starts with an optional preamble PRE consisting of a fixed sequence of N.sub.PRE synchronization bits. The preamble PRE is usually required for serial communications in order to signal the beginning of a new communication. For example, the preamble PRE may be a single bit being set to a given logic value. For example, similar to an UART based communication, the preamble PRE may consist in a single start bit being set, e.g., to low.

(18) A preamble PRE consisting of a longer sequence may be useful in order to perform a clock and data recovery (CDR) operation, i.e., an operation used to align the clock signal of the receiver 2 with the clock signal transmitter 1.

(19) For example, in the embodiment shown in FIG. 14, the receiver circuit 22a may comprise a clock and data recovery circuit 226 configure to recover a serial data signal SDI and the receiver clock signal RX_CLK from the received signal RX, i.e., in case of transmission of data, the signal SDI will contain sequentially the bits of the data packet, usually starting from the most significant bit (MSB).

(20) Specifically, such CDR 226 permits to extract the transmitted data sequence from the distorted received signal RX and to recover the associated clock signal RX_CLK. For example, the CDR circuit 226 may comprise a clock recovery circuit configured to detect the transitions in the received data signal RX and generate a periodic clock RX_CLK. Generally, two types of clock and data recovery circuits 226 exist: clock and data recovery circuits operating with a reference clock signal, generated, e.g., by an oscillator 228, and clock and data recovery circuits operating without a reference clock signal. Often the circuit 226 comprises also a decision circuit, such as one or more flip-flops, e.g., D flip-flops, connected in cascade, which sample the received data signal RX in accordance with the recovered clock signal RX_CLK. Accordingly, the sampled data signal SDI at the output of the circuit 226 usually has less jitter, skew and/or noise. Reference can be made for this purpose, e.g., to document Ming-ta Hsieh and Gerald E. Sobelman, Architectures for Multi-Gigabit Wire-Linked Clock and Data Recovery, IEEE Circuits and Systems Magazine, December 2008, showing the basic topologies of CDR circuits, which is incorporated herein by reference. For example, in the embodiment considered, a preamble PRE with N.sub.PRE=7 bits is used.

(21) In various embodiments, the receiver circuit 22a, in particular the digital processing circuit 224, may also determine whether the preamble PRE is correct, e.g., by comparing the preamble PRE with a reference preamble PRE_CFG. Generally, the reference preamble PRE_CFG may be fixed within the digital processing circuit 224 or may be provided to the processing circuit 224 by a further module. For example, in the embodiment shown in FIG. 14, the reference preamble PRE_CFG is provided by a memory 230. Generally, the memory 230 may be a volatile memory, such as a register programmed by means of the micro-processor of the receiver apparatus, or a non-volatile memory, including also a one-time-programmable (OTP) memory.

(22) In the embodiment considered, the header HD comprises moreover an address field A having a given number of bits N.sub.A. Specifically, the address field A may be used to identify the sender and/or the intended receiver(s), i.e., the sender address and/or the target address. For example, in the embodiment considered, the address field A may contain the address of a receiver or group of receivers. Accordingly, the address A allows the receivers to determine whether the subsequent strings of bits are sent to themselves and should be processed, or should be ignored. Generally, some address values may also have special meanings and may thus be reserved, i.e., these addresses do not identify transmitter or receivers.

(23) Accordingly, in various embodiments, the receiver circuit 22a, in particular the digital processing circuit 224, may be configured to determine whether the address A corresponds to one or more reference addresses A_CFG. Similar to the reference preamble PRE_CFG, the reference addresses A_CFG may be fixed within the processing circuit 224 or may be provided to the processing circuit 224 by a further module. For example, in the embodiment shown in FIG. 14, one or more reference addresses A_CFG are provided by the memory 230, which again may be a volatile memory or a non-volatile memory. Generally, also a first part (e.g., the first 8 bits) of the reference address A_CFG could be fixed and a second part (e.g., the remaining 8 bits) could be programmable.

(24) In various embodiments, the address size, i.e., the number of bits N.sub.A of the address A, is variable in order to make the communication protocol compliant with different system capabilities and/or with multiple areas of application. For example, in the embodiment considered, the address field A has 16 bits. Conversely, FIGS. 4b, 4c and 4d show the respective data packet with address fields A having a length of 12, 10 and 8 bits.

(25) For example, in the embodiment shown in FIG. 14, an address selection signal AS is used to indicate which address length should be used. For example, in the embodiment considered, the address selection signal AS may comprise two bits in order to select between an address length of 16, 12, 10 or 8 bits.

(26) For example, in the embodiment shown in FIG. 14, the address selection signal AS is provided by the memory 230, which again may be a volatile memory or a non-volatile memory. For example, in various embodiments, the reference preamble and the address selection signal AS are set once (e.g., by the producer of the receiver circuit 22a), while the reference address A_CFG of the receiver circuit 22a may be set dynamically at least in part (e.g., by the producer of the complete receiver apparatus), e.g., by programming the memory 230.

(27) Generally, the length N.sub.A of the address field A may also be determined dynamically based on a given bit sequence in the header HD. For example, different preambles PRE may be used for different address lengths or the first bits of the address field A may represent the address selection signal AS. For example, the first two bits of the address A may be used in order to select between an address length of 8, 10, 12 or 16 bits.

(28) Conversely, the data/payload frame PL includes the digital information DAT (e.g., the input data DI shown in FIG. 3, and possible other data) to be transmitted, such as data, configuration setting and/or instruction command codes, which allow the receiver apparatus to perform a defined operation. For example, in the embodiment considered, the data field DAT consists of N.sub.D=4 bits, which may indicate the button pressed on a remote control 1. Accordingly, in the embodiment considered, a television or another receiver apparatus may be switched on by including one of the addresses A_CFG of the receiver 22a of the respective receiver apparatus in the address field A and the code of the power button in the data field DAT.

(29) Detection of transmission errors may be required for communication channels, which cannot guarantee error-free operation. For this reason, in various embodiments, a number N.sub.P of additional bits P may be added, e.g., at the end of packet, thereby permitting a Cyclic Redundancy Check (CRCs) or parity check, which makes it possible for the receiver circuit 22a to detect differences introduced in the data packet by communication errors. For example, in this case, the receiver circuit 22a may reject the packet and/or arrange a retransmission.

(30) Generally, the number N.sub.P of error-checking bits P may also vary based on the number of bits to be verified. For example, in the embodiment considered, excluding the preamble, with each four bits to be checked is associated a respective parity bit P. For this reason, the packet shown in FIG. 4a may comprise 5 bits P, the packets shown in FIGS. 4b and 4c may comprise 4 bits P and the packet shown in FIG. 4d may comprise 3 bits P.

(31) Packets may also be lost or suffer from long delays. To cope with this, in various embodiments, the transmitter circuit may expect an acknowledgement of correct reception from the receiver circuit 22a within a certain amount of time. On timeouts, the transmitter circuit may assume that the packet was not received and retransmit it. In case of a permanently broken link, the retransmission has no effect so the number of retransmissions is usually limited. In this case, exceeding the retry limit may be considered as a communication error.

(32) The inventors have observed that the communication protocol shown in FIGS. 4a to 4d has several disadvantages.

(33) Specifically, due to the fact, that the address field A may have different lengths, the position of the payload, including the data field DAT and possibly the bits P changes. Accordingly, complex multiplexing logic is required, e.g., in order to select the correct bits as data bits DAT.

(34) FIGS. 5a and 5b show in this regards a first embodiment of modified data packets being adapted to transmit the same content as the respective data packets shown in FIGS. 4a to 4d.

(35) As shown in the foregoing, the address selection signal AS may be considered as a data packet format selection signal, which selects between a plurality of different data packet formats having a different total number of bits N.sub.PF.

(36) Generally, each data packet comprises: one or more fields with fixed number of bits, such as the optional preamble PRE and the data field DAT, and one or more fields with having a variable number of bits, such as the address field A and the optional bit sequence for error checking P, wherein the number of these bits is however fixed for each packet format.

(37) Moreover, when comparing the various data packet formats shown in FIGS. 4a to 4d, the number of bits of the fields with variable number, i.e., the address A and the error checking bits P, never decreases.

(38) Accordingly, in various embodiments, when switching to a packet format having a greater number of bits, the additional bits are transmitted at the end of the data packet.

(39) For example, in the embodiment considered in FIGS. 5a to 5d are again supported four packet formats for address fields with a length of 8, 10, 12 and 16 bits. In the embodiment considered, the shortest data packet BP1 is shown in FIG. 5d and corresponds substantially to the data packet shown in FIG. 4d, i.e., the data packet BP1 comprises in sequence: the optional preamble (e.g., having N.sub.PRE=7 bits), one or more address sub-fields A1 and A2 (e.g., having a total of N.sub.A=8 bits), a data field DAT (e.g., having N.sub.D=4 bits), and optional error checking bits P (e.g., N.sub.P=3 bits P1, P2 and P3). For example, in the embodiment considered, the shortest data packet BP1 has a total of N.sub.PF=21 bits.

(40) However, when changing to the next longer packet format, the packet structure of the first bits corresponds always to the packet structure of the previous shorter format and the additional bits are added at the end of the data packet.

(41) For example, in the embodiment considered, the next data packet format BP2 shown in FIG. 5c would support address fields having a total of N.sub.A=10 bits and N.sub.P=4 error checking bits P. Accordingly, two additional address bits and an additional error checking bit P4 have to be transmitted. As mentioned in the foregoing, these additional bits are transmitted at the end of the data packet. For example, as shown in FIG. 5c, the first bits of the data packet BP2 correspond to the data packet BP1 followed by the additional error checking bit P4 and an additional address sub-field A3 having two bits.

(42) Similarly, in the embodiment considered, the next data packet format BP3 shown in FIG. 5b would support address fields having a total of N.sub.A=12 bits and N.sub.P=4 error checking bits P. Accordingly, two additional address bits have to be transmitted. Again, these additional bits are transmitted at the end of the data packet, i.e., the first bits of the data packet BP3 correspond to the data packet BP2 followed by an additional address sub-field A3 having two bits.

(43) Finally, the next data packet format shown in FIG. 5a supports address fields having a total of N.sub.A=16 bits and N.sub.P=5 error checking bits P. Accordingly, four additional address bits and an additional error checking bit P5 have to be transmitted. For example, as shown in FIG. 5a, the first bits of the data packet may correspond to the data packet BP3 followed by the additional error checking bit P5 and an additional address sub-field A4 having four bits.

(44) Thus, the data packet formats shown in FIGS. 5a to 5d permit to transmit the same content as the data packet formats shown in FIGS. 4a to 4d, and only the position of the various bits within the data packet change.

(45) FIGS. 6a to 6d show a second embodiment of the data packet formats, wherein the shortest data packet BP1, i.e., the data packet for address fields A with a length of N.sub.A=8 bits, has a different format. Specifically, in the embodiment considered the data packet BP1 comprises in sequence: the optional preamble (e.g., having N.sub.PRE=7 bits), the data field DAT (e.g., having N.sub.D=4 bits), one or more address sub-fields A1 and A2 (e.g., having a total of N.sub.A=8 bits), and optional error checking bits P (e.g., N.sub.P=3 bits P1, P2 and P3). Accordingly, merely the position of the data bits DAT and the address bits A1/A2 have changed in the data packet shown in FIG. 6d. Also in this case, the longer data packet formats comprise at the beginning the bits of the previous data packet format and at the end the additional bits. Accordingly, the respective description will not be repeated and reference can be made to the description of FIGS. 5a to 5c.

(46) FIGS. 7a to 7d show a third embodiment of the data packet formats, wherein the shortest data packet BP1 has a different format. Specifically, in the embodiment considered the error checking bits P1, P2 and P3 are interleaved between the data field DAT and the address field A, e.g., at the beginning of the data field DAT, the first address sub-field A1 (e.g., having 4 bits) and the second address sub-field A2 (e.g., having 4 bits). Also in this case, the longer data packet formats comprise at the beginning the bits of the previous data packet format and at the end the additional bits. Accordingly, the respective description will not be repeated and reference can be made to the description of FIGS. 5a to 5c.

(47) In general, the communication protocol described in the foregoing supports at least two data packet formats having a different number of bits. Specifically, the shorter data packet format (e.g., BP1) comprises a plurality of fields, each field of the shorter data packet format having a given number of bits, and the longer data packet format (e.g., BP2) contains at the beginning the bits of the shorter data packet format and at the end at least one additional bit being associated with at least one field of the shorter data packet format, thereby increasing the number of bits of the respective field. For example, in the embodiments considered, the number of bits N.sub.A of the address field A are increased in this way.

(48) As mentioned in the foregoing, the data packet formats shown in FIGS. 5, 6 and 7 have the same number of bits as the respective data packet formats shown in FIG. 4 and only the position of the bits changes. However, the modified data packet formats permit a more efficient implementation of the digital processing circuit 224 used to determine the transmitted data DO based on the serial data signal SDI (or directly the received signal RX).

(49) For example, as shown in FIG. 8, the processing circuit may comprise a shift register REG having a number of bits N.sub.REG corresponding to the number of bits N.sub.PF of the longest data packet format supported, e.g., 32 bits for the embodiments considered in the foregoing.

(50) However, instead of simply loading the serial input data SDI into the shift register, the register has associated therewith one or more multiplexers 200 configured to select the input position of the register REG in which the serial data signal SDI is loaded. Specifically, in the embodiment considered, the selection is performed based on the signal AS, i.e., the address length/packet data format selection signal.

(51) In the embodiment considered, the multiplexer(s) 200 are configured to select the input position for loading the shift register REG at the following bit position POS:
POS=N.sub.REGN.sub.PF(1)
where N.sub.PF corresponds to the number of bits of the selected data packet format. For example: when the length of the address A is selected as N.sub.A=16 bits (N.sub.PF=32), the position of the input of the shift register would be set to 0, i.e., the 1.sup.st register; when the length of the address A is selected as N.sub.A=12 bits (N.sub.PF=27), the position of the input of the shift register would be set to 5, i.e., the 6.sup.th register; when the length of the address A is selected as N.sub.A=10 bits (N.sub.PF=25), the position of the input of the shift register would be set to 7, i.e., the 8.sup.th register; and when the length of the address A is selected as N.sub.A=8 bits (N.sub.PF=22), the position of the input of the shift register would be set to 10, i.e., the 11.sup.th register.

(52) In this regards, it may be observed that, when changing to the next longer packet format, the input position of the shift register REG is shifted by the number of the additional bits added at the end of the longer packet format.

(53) Accordingly, in the embodiments considered, the received bits are sequentially loaded in accordance with the clock signal RX_CLK into the shift register REG, and once having received all bits of data packet, i.e., N.sub.PF bits, the respective bits are always located in the most significant bits of the shift register REG, while the least significant bits may remain empty, i.e., the bits being associated with the shortest data packet format BP1 and which are included at the beginning of all other data packet formats are always loaded into the most significant bits of the register REG.

(54) Moreover, as shown in FIGS. 9a to 9d, the bits are always loaded into the same position, e.g., the preamble PRE is always in the positions [31:25] and the data field DAT is always in the positions [23:19]. Similarly, the sub-field A1 and A2 of the address A are always in the positions [18:15] and [13:10], respectively. Accordingly, thanks to the specific data packet format used and the selection of the position of the serial input of the shift register REG, the bit positions remain unchanged and merely the least significant bits of the shift register REG are selectively filled with the additional bits introduced with the longer data packet formats. For example, in FIG. 9c the error checking bit P4 and the sub-field A3 of the address A are loaded in the positions [9] and [8:7], respectively. Similarly, the additional two bits of the sub-field A3 of the address A are loaded in the positions [6:5]. Finally, the error checking bit P5 and the sub-field A4 of the address A are loaded in the positions [4] and [3:0] in FIG. 9a. In case the respective bits are not transmitted, the respective positions remain unchanged, e.g., remain set to 0.

(55) This is also highlighted in FIGS. 10a to 10d which show possible load operations of the shift register REG for the different packet formats.

(56) Specifically, in the example considered in FIG. 10a, the bits of the register REG are set all to 0 at a time T0, corresponding thus to a reset condition. Moreover, in FIG. 10a the longest packet format is selected, i.e., 16 address bits and the position of the input of the shift register would be set to 0.

(57) At a time T0 the first bit (i.e., the first preamble bit) is received, which is loaded thus in the bit position 0. During the following clock cycles, the subsequent bits are received and the bits are shifted form the input position to the MSB bits of the shift register. For example, at the time T12, 12 bits have been received and the content of the shift register could be 0000000 00000 00000 00001 10110 10111. The operation proceeds until all bits have been received at a time T32 (i.e., after 32 clock cycles) and the content of the shift register is, e.g., 0110110 10111 10001 00110 10010 01100. Accordingly, in the example considered, the data packet shown in FIGS. 7a to 7d would have the following content: preamble PRE: 0110110; data field DAT: 0111 corresponding to a hexadecimal code 7; address field A: 0001 0110 0010 1100 corresponding to a hexadecimal code 162C; and error checking bits P: 11010.

(58) Similarly, FIG. 10b shows an example for an address length of 12 bits, where the position of the input of the shift register would be set to 5. In this case, the data packet contains only 27 bits, i.e., all bits have been received at a time T27 and the content of the shift register is, e.g., 011011010111 10111 00110 10010 01100 00000. Accordingly, in the example considered, the data packet shown in FIGS. 7a to 7d would have the following content: preamble PRE: 0110110; data field DAT: 0111 corresponding to a hexadecimal code 7; address field A: 0110 0010 1100 0000 corresponding to a hexadecimal code 62C0, with the last four bits being unused; and error checking bits P: 10100, with the last error checking bit being unused.

(59) Similarly, FIG. 10c shows an example for an address length of 10 bits, where the position of the input of the shift register would be set to 7. In this case, the data packet contains only 25 bits, i.e., all bits have been received at a time T25 and the content of the shift register is, e.g., 011011010111 10111 11000 11011 00000 00000. Accordingly, in the example considered, the data packet shown in FIGS. 7a to 7d would have the following content: preamble PRE: 0110110; data field DAT: 0111 corresponding to a hexadecimal code 7; address field A: 1000 1011 0000 0000 corresponding to a hexadecimal code 8600, with the last six bits being unused; and error checking bits P: 11100, with the last error checking bit being unused.

(60) Finally, FIG. 10d shows an example for an address length of 8 bits, where the position of the input of the shift register would be set to 10. In this case, the data packet contains only 22 bits, i.e., all bits have been received at a time T22 and the content of the shift register is, e.g., 011011010111 10111 10010 01100 00000 00000. Accordingly, in the example considered, the data packet shown in FIGS. 7a to 7d would have the following content: preamble PRE: 0110110; data field DAT: 0111 corresponding to a hexadecimal code 7; address field A: 0010 1100 0000 0000 corresponding to a hexadecimal code 2C00, with the last eight bits being unused; and error checking bits P: 11000, with the last two error checking bits being unused.

(61) The use of a shift register REG, instead of a complete FIFO (First-In First-Out) memory has the advantage that no complex FIFO control logic is required. Moreover, the bits in the shift register REG may be processed completely in parallel.

(62) For example, as shown in FIG. 11, the receiver circuit 22a, in particular the digital processing circuit 224, may comprise a preamble verification circuit 202 configured to generate a signal PRE_OK indicating whether the received preamble PRE (if supported by the packet data format) corresponds to the reference preamble PRE_CFG. For this purpose, the circuit 202 may simply perform a bit level comparison between the first N.sub.PRE bits stored in the register REG, e.g., 7 bits for the exemplary preamble, and the bits of the reference preamble PRE_CFG.

(63) Similarly, the receiver circuit 22a, in particular the digital processing circuit 224, may comprise an address verification circuit 204 configured to generate a signal ADDR_OK indicating whether the received address A corresponds to the reference address A_CFG. Generally, the circuit 204 may also compare sequentially or in parallel the received address A with a plurality of reference addresses A_CFG.

(64) In various embodiment, the circuit 202 performs for this purpose a bit level comparison between the bits assigned to the address field of the longest data packet format, i.e., the sub-fields A1, A2, A3, A3 and A4 having a total of N.sub.A=16 bits, and the bits of the reference address A_CFG, which also has 16 bits. Accordingly, by setting the unused bits of the reference address A_CFG to the reset value of the register REG, the comparison will be performed for the received address bits, while the comparison for the empty bits will intrinsically be positive. Generally, the address verification circuit 204 could also receive the signal AS and perform the comparison only for the address bits indeed received, thereby reducing the risk that a user incidentally configured an address reference signal A_CFG having the wrong content for the address bits being unused in the selected data packet format.

(65) Similarly, FIG. 12 shows an embodiment of an error checking circuit 206. Specifically, in the embodiment considered, the error checking circuit 206 receives at input the data field DAT, the address field A (including the sub-fields A1, A2, A3, A3 and A4) and the error checking bits P.

(66) Accordingly, in the embodiment considered, the error checking circuit 206 performs the same operation already performed in the transmitter circuit in order to compute error checking bits P for the received data file DAT and the received address field A and then compares the computed error checking bits with the received error checking bits P (e.g., the bits P1, P2, P3 P4 and P5 in the bit positions [24], [19], [14], [9] and [4], respectively).

(67) For example, in the embodiment considered, the error checking bits P are parity bits. Generally, the parity bits P may be even parity bits or odd parity bits. In the case of even parity, the number of bits whose value is 1 in a given set is counted. If that total is odd, the parity bit value is set to 1, making the total count of 1's in the set an even number. If the count of ones in a given set of bits is already even, the parity bit's value remains 0. In the case of odd parity, the situation is reversed. Instead, if the sum of bits with a value of 1 is odd, the parity bit's value is set to zero. And if the sum of bits with a value of 1 is even, the parity bit value is set to 1, making the total count of 1's in the set an odd number. Accordingly, even parity is a special case of a cyclic redundancy check (CRC), where the 1-bit CRC is generated by the polynomial x+1.

(68) For example, in the embodiment considered, the parity bits P are assigned in the following way: parity bit P1 for the data field DAT, parity bit P2 for the address sub-field A1, parity bit P3 for the address sub-field A2, parity bit P4 for the combination of the address sub-field A3 and the address sub-field A3, and parity bit P5 for the address sub-field A4.

(69) Accordingly, in the embodiment considered, each parity bit is assigned to a unique sequence of four bits.

(70) Accordingly, respective parity checking circuit 208, 210, 212, 214 and 216 may be used to compute separately the parity bits for the data field DAT, the address sub-field A1, the address sub-field A2, the combination of the address sub-field A3 and the address sub-field A3 and the address sub-field A4, respectively, and determine whether the computed parity bits corresponds to the respective received parity bits. For example, in the embodiment considered, the circuits 208, 210, 212, 214 and 216 generate respective signals DAT_OK, A1_OK, A2_OK, A3_OK and A4_OK indicating whether the received data field DAT, address sub-field A1, address sub-field A2, combination of the address sub-field A3 and the address sub-field A3 and address sub-field A4 are correct.

(71) Accordingly, a further circuit 218 may be used to logically combine the signals DAT_OK, A1_OK, A2_OK, A3_OK and A4_OK in order to generate a signal P_OK indicating that the received data DAT and address A do not contain errors.

(72) Generally, the error checking circuit 206 may also perform more complex operations, e.g., in order to recover errors by means of Reed Solomon Codes. However, in case of ultra-low power communication, a simple parity check may be sufficient.

(73) In the embodiment considered, the data field DAT has a fixed length of N.sub.D bits. Accordingly, the content of this field DAT, e.g., the bits [23:20] in the exemplary embodiment, may be read in parallel by means of a parallel data output signal PDO. Generally, the data field DAT may also be read sequentially for N.sub.D clock cycles by means of a serial data output signal SDO being connected to the first bit of the data field DAT (e.g., bit [23]).

(74) For example, as shown in FIG. 13, a logic circuit 220, such as an AND gate, may be used to generate an enable signal EN indicating whether the received data DAT should be processed by the receiver apparatus, e.g., because the preamble does not contain errors (signal PRE_OK), the received data DAT and address A do not contain errors (signal P_OK) and the received address A corresponds to one of the addresses A_CFG assigned to the receiver circuit (signal ADDR_OK). For example, the signal EN may be used to store the parallel data signal PDO in a register 222 (having, e.g., 4 bits). In this case the output of the register 222 may provide the transmitted data DO.

(75) Accordingly, in the embodiments described in the foregoing, the digital processing circuit 224 receives and decodes the address and data bits coming from a receiver 20, such as a radio frequency modulator. The digital processing circuit 224 supports variable address sizes (16, 12, 10 and 8 bits) and the respective reference addresses A_CFG may be pre-configured, e.g., by means of a one-time programmable memory 230 based on anti-fuse cells, or received from a further processing circuit. In various embodiments, the digital processing circuit 224 is able to detect errors in the address and data bits.

(76) The proposed mechanism and the related hardware digital circuit are thus flexible, fast and simple with improved computational resources in terms of chip-area and power consumption. In fact, the same hardware circuit may be used for variable address sizes without having to add further logic.

(77) FIG. 15 shows a second embodiment of the receiver circuit.

(78) Specifically, in the embodiment two shift registers REGa and REGb are used instead of the single shift register REG shown in FIGS. 8 to 10.

(79) More particular, the first shift register REGa is used to store the bits of the shortest packet format BP1 and the second shift register REGb is used to store the additional bits when a longer packet format BP2, BP3 or BP4 is selected, i.e., the additional bits of the address sub-fields A3, A3 and A4 and the additional error checking bits P4 and P5. Accordingly, in the embodiment considered, the register REGb has 10 bits, and the register REGb has 22 bits, e.g., numbered [31:10] just for convenience.

(80) Specifically, in the embodiment considered, a first multiplexer 200a is used to connect selectively the serial data signal SDI to the serial input of the register REGa or the serial input of the register REGb as a function of a signal REGa_LC indicating whether the register REGa has been loaded completely or not. Specifically, when the signal REGa_LC indicates that the register REGa has not been loaded completely, the serial data signal SDI is connected to the serial input of the register REGa, in particular the least significant bit (e.g., bit 10 for the exemplary bit numeration), and incoming bits are loaded sequentially in the shift register REGa. Conversely, when the signal REGa_LC indicates that the register REGa has been loaded completely, the serial data signal SDI is connected to the serial input of the register REGb and possible further incoming bits are loaded sequentially in the shift register REGb.

(81) However, in this case, the serial input position of the register REGb is not fixed, but determined (similar to the register REG) by means of a one or more multiplexers 200b as a function of the signal AS. For example, in the embodiment considered, the multiplexer(s) 200b are configured to select the input position for loading the shift register REGb at the following bit position POS:
POS=N.sub.REGb(N.sub.PFN.sub.REGa)(2)

(82) where N.sub.PF corresponds to the number of bits of the selected data packet format, and N.sub.REGa and N.sub.REGb are the number of bits of the registers REGa and REGb, respectively. For example, considering N.sub.REGa=22 and N.sub.REGb=10: when the length of the address A is selected as N.sub.A=16 bits (N.sub.PF=32), the position of the input of the shift register REGb would be set to 0, i.e., the 1.sup.st register; when the length of the address A is selected as N.sub.A=12 bits (N.sub.PF=27), the position of the input of the shift register REGb would be set to 5, i.e., the 6.sup.th register; when the length of the address A is selected as N.sub.A=10 bits (N.sub.PF=25), the position of the input of the shift register REGb would be set to 7, i.e., the 8.sup.th register; and when the length of the address A is selected as N.sub.A=8 bits (N.sub.PF=22), the position of the input of the shift register would be set to 10, i.e., the 11.sup.th register, which however does not exist, because no additional bits are indeed expected in this case.

(83) Thus also in this case, when changing to the next longer packet format, the input position of the shift register REGb is shifted by the number of the additional bits added at the end of the longer packet format.

(84) FIG. 16 shows a similar embodiment, in which, however, only a subset of the bits of the shortest packet format BP1 are stored in the register REGa, i.e., the number of bits N.sub.REGa is smaller than the number of bits of the packet format BP1, while the sum N.sub.REGaN.sub.REGa still corresponds to the number of bits of the longest packet format BP4.

(85) For example, in the embodiment considered, only the preamble PRE, the first error checking bit P1 and the data field DAT are stored in the register REGa and the remaining bits are stored in the register REGb, i.e., N.sub.REGa=12 and N.sub.REGb=20. Accordingly, in this case, the first 12 bits are loaded into the register REGa and once the signal REGa_LC indicates that the register REGa is fully loaded, following bits are loaded into the register REGb, wherein the input position of the register REGb is selected by means of the multiplexer 200b according to equation (2), i.e.: when the length of the address A is selected as N.sub.A=16 bits (N.sub.PF=32), the position of the input of the shift register REGb would be set to 0, i.e., the 1.sup.st register; when the length of the address A is selected as N.sub.A=12 bits (N.sub.PF=27), the position of the input of the shift register REGb would be set to 5, i.e., the 6.sup.th register; when the length of the address A is selected as N.sub.A=10 bits (N.sub.PF=25), the position of the input of the shift register REGb would be set to 7, i.e., the 8.sup.th register; and when the length of the address A is selected as N.sub.A=8 bits (N.sub.PF=22), the position of the input of the shift register would be set to 10, i.e., the 11.sup.th register.

(86) Again, when changing to the next longer packet format, the input position of the shift register REGb is shifted by the number of the additional bits added at the end of the longer packet format.

(87) The processing part of the content of the registers REGa and REGb may remain unchanged compared to the embodiments having only a single register REG. Accordingly, reference can be made to FIGS. 11, 12 and 13 and the respective description, showing how the content of the respective bits/fields stored now in the registers REGa and REGb may be processed, in particular with regards to the preamble verification (block 202) the address verification (block 204) and the error checking function (block 206).

(88) As mentioned in the foregoing, the signal REGa_LC indicates whether the register REGa has been loaded completely or not. In the embodiments shown in FIGS. 15 and 16, this may be obtained by means of a counter 232 configured to determine whether a count value (being incremented each time a new bit is received) has reached the number of bits N.sub.REGa of the register REGa (e.g., 22 for FIG. 15 and 12 for FIG. 16), wherein the signal REGa_LC is set: to a first logic value, e.g., low, when the count value is smaller than the number of bits N.sub.REGa, and

(89) to a second logic value, e.g., high, when the count value is equal or greater than the number of bits N.sub.REGa.

(90) FIGS. 17a to 17c show instead embodiments, in which the signal REGa is determined directly as a function of the content of the register REGa.

(91) Specifically, in the embodiment shown in FIG. 17a, an additional bit LC is added to the shift register REGa as MSB bit (e.g., [32] in the embodiment considered). In this case, when the shift register is reset, all bits are set to a first logic value, e.g., low, except the LSB bit (e.g., [20] in the embodiment considered), which is set to a second logic value, e.g., high. Accordingly, when data are received sequentially via the serial input of the shift register REGa, the bit with the second logic value is shifted form the least significant bit position to the most significant bit position. Accordingly, it is sufficient to determine the signal REGa_LC as a function of the content of the MSB bit LC (e.g., [32] in the embodiment considered). For example, in the embodiment considered, the signal REGa_LC corresponds directly to the content of the bit LC in the register REGa.

(92) Conversely, FIG. 17b shows an embodiment, in which no additional bit LC is added, but the expected content of the register REGa is used to determine the signal REGa_LC. For example, considering the previous exemplary preamble 0110110 the second preamble bit may be used as indicator whether the register REGa has been loaded fully, i.e., the signal REGa_LC may be determined as a function of the second preamble bit (e.g., [30] in the embodiment considered). For example, in the embodiment considered, the signal REGa_LC corresponds directly to the content of the second preamble bit, which should be high when the register REGa has been loaded fully.

(93) This embodiment has however the disadvantage that the reference preamble sequence PRE_CFG may not be changed, and errors in the communication may also trigger the signal REGa_LC.

(94) Accordingly, FIG. 17c shows an embodiment, in which the complete preamble field PRE is verified and the signal REGa_LC is asserted by means of a block 202 only when the preamble field (e.g., bits [31:15] in the embodiment considered) corresponds to the reference preamble PRE_CFG. This embodiment does not add any overhead, because the preamble verification circuit 202 may already be used to check the preamble field (see FIG. 11). In fact, in this case it is sufficient to determine the signal REGa_LC as a function of the preamble verification signal PRE_OK.

(95) The use of several shift registers has the advantage that, once having received a given number of bits (N.sub.REGa) the content of the register REGa remains stable, while further bits may still be received and stored in the register REGb.

(96) This behavior may thus be used to determine the used packet format, e.g., the length N.sub.A of the address field A and consequently the signal AS, based on the content of the transmitted data already stored in the register REGa.

(97) For example, in the embodiment shown in FIG. 15, the address selection signal AS may be determined as a function of the address sub-fields A1 and/or A2. For example, the signal AS may correspond to the first two bits of the address sub-field A1 (e.g., bits [18:17] in the embodiment considered).

(98) Conversely, FIG. 18 shows an embodiment, in which the packet format BP1 (and accordingly also the longer formats BP2-BP4) comprise an additional address selection field AS (e.g., bits [26:25] in the embodiment considered) and possibly a respective parity bit P0 (e.g., bit [19] in the embodiment considered). In this case, the register REGa has to have a sufficient number of bits in order to receive also this address selection field, and the address selection field AS (and the possible error checking bits P0) preferably follows immediately the preamble PRE.

(99) As mentioned before, also different preambles PRE may be used for different address lengths. For example, in this case a set of preamble verification circuits 202 could be used in order to compare (similar to FIG. 17c) the content of the preamble field PRE stored in the register REGa with respective reference preambles PRE_CFG, one for each possible packet format (BP1-BP4), e.g., four preamble verification circuits 202 with respective different reference preambles PRE_CFG. Accordingly, only one of the preamble verification circuits 202 would indicate a correct preamble and this signal may be used (similar to a one-hot encoding) in order to determine the address selection signal AS.

(100) Generally, the receiver circuit 22a extracts thus data DO from a serial data signal SDI containing a data packet. The data packet may have a first or a second data packet format (e.g., BP1 or BP2) based on the selection signal AS. In various embodiments, the receiver circuit 22a comprises one or more shift registers having a total number of bits being equal or greater than the number of bits of the second/longer data packet format. This receiver comprises moreover a switching circuit 200, 200a/200b associated with the shift registers, which is configured to selectively connect the serial data signal SDI to one of the serial inputs as a function of the selection signal AS.

(101) Specifically, in the embodiment shown in FIG. 8, a single shift register REG is used, while two shift registers are used in the embodiments shown in FIGS. 15, 16 and 18. In both embodiments, when the first data packet format BP1 has been selected and once having received the bits of the data packet, the respective bits are loaded/stored in given positions of the shift registers. However, when the second data packet format BP2 has been selected and once having received the bits of the data packet, the switching circuit ensures that the bits of the first data packet format BP1 being included in the second data packet format (BP2) are again loaded/stored in the same positions of the shift registers.

(102) For example, in the embodiment shown in FIG. 8, a first input position of the shift register REG is selected for the reception of the bits of the serial data signal SDI when the first packet format BP1 is selected. Conversely, when the second data packet format BP2 has been selected, a second input position is selected for the reception of the bits, wherein the second input position corresponds to the first input position shifted by the number of the additional bits introduced in the second data packet format.

(103) Conversely, in FIGS. 15, 16 and 18, an input position of the first shift register REGa is selected for the reception of a given number of bits of the serial data signal SDI and, once the given number of bits has been received, an input position of the second shift register REGb is selected for the reception of further bits.

(104) Specifically, in FIG. 15, the first register REGa has a number of bits corresponding to the number of bits of the first data packet format BP1 and the bits of the first data packet format BP1 are loaded always into the first shift register REGa and possible additional bits of the second data packet format are loaded into the second shift register REGb.

(105) Conversely, in FIG. 16, the first register REGa has a number of bits being smaller than the number of bits of the first data packet format BP1. In this case, the switching circuit selects a first input position of the second shift register REGb for the reception of further bits in accordance with the first packet data format BP1, and a second input position for the reception of further bits in accordance with the second packet data format BP2, wherein the second input position corresponds to the first input position shifted by the number of the additional bits introduced in the second data packet format BP2.

(106) Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention, as defined by the ensuing claims.

(107) The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.