PULSE-AMPLITUDE MODULATION TRANSCEIVER, FIELD DEVICE AND METHOD FOR OPERATING THE PULSE-AMPLITUDE MODULATION TRANSCEIVER

Abstract

A PAM transceiver configured to process an electrical data signal having at least three states includes an electronic circuit comprising: a data interface configured to connect to a duplex communication channel; a first circuit section connected to the data interface; and a second circuit section connected to the data interface. The first circuit section includes an equalizer for compensating for distortions in the data signal and an interpreter downstream of the equalizer for recognizing symbols. The second circuit section includes a delay unit for time-shifting the data signal and an MMA processor for recognizing a signal phase of the data signal. The first circuit section and the second circuit sections are routed to the MMA processor. The second circuit section has a finite impulse response filter configured to monotonize an impulse response of the communication channel.

Claims

1-12. (canceled)

13. A pulse amplitude modulation (PAM) transceiver configured to process a received electrical data signal having at least two states, wherein the data signal comprises a sequence of states, each state representing an information symbol and a pulse of the data signal is assigned to each symbol, the PAM transceiver comprising: an electronic circuit including a first circuit section and a second circuit section; a data interface configured to connect to a duplex communication channel and configured to digitize the data signal, the data interface including an analog/digital converter configured to digitize the data signal received by the data interface and to supply the digitized data signal to the first circuit section and to the second circuit section; wherein the first circuit section is connected to the data interface and the first circuit section includes: an equalizer to compensate for distortions in the data signal caused by the communication channel; and an interpreter arranged downstream of the equalizer for recognizing symbols transmitted by the data signal; wherein the second circuit section is connected to the data interface and the second circuit section includes: a delay unit for time-shifting the data signal; a Mueller-Müller algorithm (MMA) processor for recognizing a signal phase of the data signal, the MMA processor having a first input and a second input, wherein the first circuit section is connected to the first input and the second circuit section is connected to the second input; and an adjustable finite impulse response filter configured to symmetrize an impulse response of the communication channel.

14. The PAM transceiver according to claim 13, wherein the adjustable finite impulse response filter is adjustable by means of three coefficients, wherein the coefficients are adjustable on the basis of a symbol associated with a pulse, of a previous state associated with an immediately preceding pulse, and of a later state associated with an immediately subsequent pulse, and wherein the filter has a property of symmetrizing an “earlier state-symbol—later state” sequence with respect to an impulse response in a state of a matching or ideal phase.

15. The PAM transceiver according to claim 13, wherein the equalizer is configured to compare states that are interpreted by the interpreter and associated with respective pulses with non-interpreted states associated with corresponding pulses and, in the absence of a match, to vary equalization parameters adaptively and thereby create a match.

16. The PAM transceiver according to claim 15, wherein the first circuit section further includes a first feedback loop from an output of the interpreter to the equalizer.

17. The PAM transceiver according to claim 14, wherein the three coefficients of the filter can be determined by measuring or knowing the impulse response of the communication channel, or wherein the three coefficients of the filter can be determined via adjusted equalization parameters of the equalizer.

18. The PAM transceiver according to claim 13, wherein the PAM transceiver is configured to determine a clock frequency of the data signal via the MMA processor and to synchronize communication via the communication channel.

19. The PAM transceiver according to claim 18, wherein the MMA processor is configured to provide the data interface including the analog/digital converter with information about a phase between a sampling point of the MMA processor and the data signal, wherein a second feedback loop is configured to transmit the information to the data interface or to the analog/digital converter.

20. The PAM transceiver according to claim 13, wherein the PAM transceiver is configured to process encoded data signals and has a signal encoder as well as a signal decoder.

21. The PAM transceiver according to claim 13, further comprising: an echo suppressor for suppressing signal echoes in the data signal caused by the PAM transceiver.

21. A field device of measurement/automation technology, comprising: a transducer for capturing a measured variable and outputting a measurement signal corresponding to the measured variable; an electronic measuring/operating circuit for operating the measuring transducer, for evaluating the measurement signal, and outputting measurement values of the measured variable; a pulse amplitude modulation (PAM) transceiver configured to process a received electrical data signal having at least two states, wherein the data signal comprises a sequence of states, each state representing an information symbol and a pulse of the data signal is assigned to each symbol, the PAM transceiver comprising: an electronic circuit including a first circuit section and a second circuit section; a data interface configured to connect to a duplex communication channel and configured to digitize the data signal, the data interface including an analog/digital converter configured to digitize the data signal received by the data interface and to supply the digitized data signal to the first circuit section and to the second circuit section; wherein the first circuit section is connected to the data interface and the first circuit section includes: an equalizer to compensate for distortions in the data signal caused by the communication channel; and an interpreter arranged downstream of the equalizer for recognizing symbols transmitted by the data signal; wherein the second circuit section is connected to the data interface and the second circuit section includes: a delay unit for time-shifting the data signal; a Mueller-Müller algorithm (MMA) processor for recognizing a signal phase of the data signal, the MMA processor having a first input and a second input, wherein the first circuit section is connected to the first input and the second circuit section is connected to the second input; and an adjustable finite impulse response filter configured to symmetrize an impulse response of the communication channel; and a housing for housing the electronic measuring/operating circuit and PAM transceiver, wherein the field device is configured to transmit and/or receive the data signal via the PAM transceiver.

23. A method for synchronizing a pulse amplitude modulation (PAM) transceiver with an incoming data signal, the method comprising: providing a pulse amplitude modulation (PAM) transceiver configured to process a received electrical data signal having at least two states, wherein the data signal comprises a sequence of states, each state representing an information symbol and a pulse of the data signal is assigned to each symbol, the PAM transceiver comprising: an electronic circuit including a first circuit section and a second circuit section; a data interface configured to connect to a duplex communication channel and configured to digitize the data signal, the data interface including an analog/digital converter configured to digitize the data signal received by the data interface and to supply the digitized data signal to the first circuit section and to the second circuit section; wherein the first circuit section is connected to the data interface and the first circuit section includes: an equalizer to compensate for distortions in the data signal caused by the communication channel; and an interpreter arranged downstream of the equalizer for recognizing symbols transmitted by the data signal; wherein the second circuit section is connected to the data interface and the second circuit section includes: a delay unit for time-shifting the data signal; a Mueller-Müller algorithm (MMA) processor for recognizing a signal phase of the data signal, the MMA processor having a first input and a second input, wherein the first circuit section is connected to the first input and the second circuit section is connected to the second input; and an adjustable finite impulse response filter configured to symmetrize an impulse response of the communication channel; comparing states that are interpreted by the interpreter and associated with respective pulses, with non-interpreted states associated with corresponding pulses and, in the absence of a match, varying equalization parameters adaptively and thereby creating a match in a first method step; determining the three coefficients of the filter by means of adjusted equalization parameters of the equalizer in a second method step and synchronizing the PAM transceiver with the incoming data signal by means of the MMA processor in a third method step.

24. The method according to claim 23, wherein the synchronization includes determining a phase of the data signal.

Description

[0060] The invention is now described with reference to exemplary embodiments.

[0061] FIG. 1 illustrates an exemplary embodiment of a PAM transceiver according to the invention.

[0062] FIG. 2 illustrates an exemplary PAM-5 signal.

[0063] FIG. 3 illustrates an exemplary embodiment of a method according to the invention.

[0064] FIG. 4 illustrates two exemplary field devices according to the invention, which are connected by a communication channel.

[0065] FIG. 1 shows a schematic circuit diagram of an electrical circuit 11 of an exemplary PAM transceiver 10 according to the invention (PAM=pulse-amplitude modulation), which is configured to enable communication by means of a communication channel 30. Data signals transmitted via the communication channel have a pulse-amplitude modulation in which at least two states, and in particular at least three states, are distributed around a voltage zero point; see FIG. 2. The states are in each case given by a voltage level. The data signal preferably has a pseudo-random encoding so that a power transmitted via the communication channel is limited to an unproblematic limit value. The electrical circuit 11 has a data interface 12 to the communication channel 30, wherein an analog/digital converter 12.1 digitizes a received analog data signal. A digital/analog converter 12.2 converts digital information to be transmitted into an analog PAM signal. The electrical circuit 11 has a signal receiving section and in the case of a duplex communication version, as shown here, can have a signal transmitting section. The sections mentioned are indicated by means of the directional arrows. The signal receiving section has a first circuit section 11.1, a second circuit section 11.2, and an MMA processor 16 (short for Mueller-Müller algorithm), wherein the first circuit section is connected to a first input 16.1 of the MMA processor, and wherein the second circuit section is connected to a second input 16.2 of the MMA processor.

[0066] After digitization by the analog/digital converter 12.1 in the first circuit section, the data signal D acquired by means of the data interface is at least partially freed of distortions by an equalizer 13 or is at least partially equalized, said distortions being caused by the communication channel. A downstream interpreter 14 interprets the digitized data signal and in each case assigns a symbol to states associated with the pulses of the data signal. The assignment of the symbols is based on voltages of the incoming states or on digital voltage values which represent voltages of the analog data signal. The equalizer can preferably comprise an adaptive filter, which filter sets filter coefficients or equalization parameters such that symbols output by the interpreter match states transmitted to the interpreter. During a learning phase, filter coefficients are gradually adjusted such that the voltage values better and better match the assigned symbols. For this purpose, a first feedback loop 18.1 can be set up as shown by way of example in FIG. 1. Equalizers with adaptive filter are already state of the art, and a person skilled in the art can look for a reasonable implementation for his purposes. The setting of the filter coefficients requires compensation of an impulse response of the data channel.

[0067] The data signal D acquired by means of the data interface is delayed by a delay unit 15 in the second circuit section running in parallel to the first circuit section, and at least partially freed by a finite impulse response filter 17 of distortions caused by the communication channel, at least for the range of the impulse response evaluated by the MMA processor.

[0068] The adjustable filter 17 has a property to symmetrize an impulse response of the communication channel.

[0069] The filter can, for example, be a “finite impulse response” filter, wherein the data signal supplied to the MMA processor is mixed with itself. The filter 17 has three filter coefficients, the three filter coefficients concerning, for example, a number of mixtures, mixing strength, and time-shifting of the mixtures.

[0070] According to the invention, these filter coefficients are set on the basis of the filter coefficients of the equalizer 13 or by measuring or knowing the impulse response of the communication channel 30. As shown here, the equalizer 13 can have an electrical data connection to the filter 17 for the purpose of transmitting the filter coefficients to the filter 17. Alternatively, the filter 17 can also have an input for the purpose of inputting data relating to the impulse response or inputting the filter coefficients.

[0071] After setting the filter coefficients of the finite impulse response filter 17, an impulse response from a totality of communication channel and second circuit section to a voltage pulse corresponding to a delta distribution or to a rectangular signal in the range of a maximum amplitude of the impulse response has a monotonic or in particular symmetrical course, which is necessary for a correct functioning of the MMA processor or of an underlying Mueller-Müller algorithm according to IEEE Transactions on Communications, vol. COM-24, no. 5, May 1976.

[0072] The MMA processor is configured to execute the Mueller-Müller algorithm. Here, symbols S recognized by the interpreter and states Z associated with the data signal are supplied to the MMA processor, wherein the MMA processor outputs values according to the following calculation rule: MM=(Z.sub.n-S.sub.n−1)-(S.sub.n-Zn.sub.n−1), where n or n−1 denotes an n-th or n−1-th pulse of the data signal. With a well-adjusted PAM transceiver or well-adjusted sampling phase of the PAM transceiver, MM is equal to 0; values not equal to 0 can be used to adjust the signal phase or sampling phase and/or clocking of the PAM transceiver. However, the MMA processor is dependent on a total impulse response in the state input being substantially monotonic in a region of a maximum of the total impulse response.

[0073] The PAM transceiver additionally has a signal decoder 21 and, in the case of a duplex communication version, a signal encoder 20. The signal decoder is configured to convert the pseudo-random encoding into a computer-readable binary data signal. The signal encoder is accordingly configured to create from a computer-readable binary data signal a PAM data signal for transmission by means of the communication channel 30.

[0074] As shown here, the PAM transceiver can in the case of a duplex communication version have an echo suppressor 19, which is configured to suppress signal echoes occurring internally, since said signal echoes cannot be completely prevented by the data interface.

[0075] FIG. 2 illustrates an exemplary amplitude-modulated data signal, a PAM-5 signal with 5 states Z1 to Z5. Each state has a duration which corresponds to a pulse T of the data signal D. By setting up more than two states, the information density of the data signal is increased. However, due to interferences, the data signal suffers state decay, which is expressed in an initial stage as indicated by a rounding of the signal edges. In the advanced stage, state decay leads to adjacent states merging and mixing. With knowledge of the channel impulse response of the channel, the decay can be compensated at least partially, or the data signal can be largely conditioned. However, PAM signals are not limited to 5 states but can generally have two or more states or signal levels.

[0076] FIG. 3 illustrates an exemplary method 100 according to the invention for synchronizing a receiving PAM transceiver with a transmitting PAM transceiver, wherein symbols output by the interpreter in a first method step 101 are compared with input states associated with the same pulses. In this case, a difference between an expected voltage value corresponding to a respective symbol and an actually applied voltage value can be used in a second method step 102 to adjust filter coefficients in order to minimize the difference between the expected voltage value and the actually applied voltage value and to thereby improve the “state-symbol” assignment. A sequence of method steps 101 and 102 is repeated with subsequent clocking of the data signal until sufficient convergence of the filter coefficients has taken place. A person skilled in the art will select limit values for such a convergence according to his needs.

[0077] When the maximum value is reached or undershot, a synchronization between PAM transceivers communicating with one another can be carried out in a third method step 103.

[0078] FIG. 4 illustrates two exemplary field devices 1 of measurement/automation technology, which are connected by means of a communication channel 30. The field devices 1 each have a measuring transducer 2 for capturing a measured variable, wherein the measuring transducers are configured to each output a measurement signal corresponding to the measured variable and to transmit it to an electronic measuring/operating circuit 3 of the respective field device. The electronic measuring/operating circuit is configured to operate the respective measuring transducer and to provide and, if necessary, output measurement values of the measured variables. The field devices in each case have a PAM transceiver 10 according to the invention. In contrast to what is shown here, the communication link 30 can also run indirectly via, for example, an edge device or, in the case of greater distances, via a signal conditioner.

LIST OF REFERENCE SIGNS

[0079] 1 Field device of measurement/automation technology

[0080] 2 Measuring transducer

[0081] 3 Electronic measuring/operating circuit

[0082] 4 Housing

[0083] 10 PAM transceiver

[0084] 11 Electronic circuit

[0085] 11.1 First circuit section

[0086] 11.2 Second circuit section

[0087] 12 Data interface

[0088] 12.1 Analog/digital converter

[0089] 12.2 Digital/analog converter

[0090] 13 Equalizer

[0091] 14 Interpreter

[0092] 15 Delay unit

[0093] 16 MMA processor

[0094] 16.1 First input

[0095] 16.2 Second input

[0096] 17 Finite impulse response filter

[0097] 18.1 First feedback loop

[0098] 18.2 Second feedback loop

[0099] 19 Echo suppressor

[0100] 20 Signal encoder

[0101] 21 Signal decoder

[0102] 30 Communication channel

[0103] 100 Method

[0104] 101 First method step

[0105] 102 Second method step

[0106] 103 Third method step

[0107] D Data signal

[0108] S Symbol

[0109] T Pulse

[0110] Z State