Gated Ring Oscillator with Constant Dynamic Power Consumption

Abstract

A pure digital ring oscillator with constant power consumption as oscillation frequency is adjusted. Circuit topology includes a multiplexer implemented in NAND gates and a delay element positioned after a path selection NAND gate of that multiplexer such that delay element transistors may not toggle if the non-delaying signal path is selected. Assuming a delay element oscillation frequency f and a total capacitance C, and also assuming a plurality N of delay gates each characterized by a propagation delay t1 and a capacitance C1 such that C=C1*N, the ring oscillator of the present invention is characterized by a C value that is proportional to N and an f value that is inversely proportional to N. Furthermore, each of the N delay gates as well as the input and output gates of the multiplexer are characterized by a common capacitance-to-propagation delay ratio=C1/t1.

Claims

1. A ring oscillator comprising: a delay element comprising a first plurality of delay gates each of a common circuit type characterized by a common propagation delay t1 and a common capacitance C1; and a multiplexer comprising a second plurality of delay gates each of the common circuit type and including a first input gate, a second input gate, an output gate, and a selection line; wherein the delay element is positioned along a delayed circuit path defined between the first input gate and the output gate of the multiplexer; wherein the selection line is operable to switch, at an oscillation frequency f, an input signal between the delayed circuit path and a non-delayed circuit path defined between the second input gate and the output gate of the multiplexer; wherein a total capacitance C of the first and second pluralities of delay gates is proportional to a sum of the first plurality of delay gates and of the second plurality of delay gates, defining a delay gate count N, and the oscillation frequency f is inversely proportional to the delay gate count N; and wherein each of the first plurality of delay gates and of the second plurality of delay gates is characterized by a common capacitance-to-propagation delay ratio C1/t1.

2. The ring oscillator according to claim 1 wherein the first plurality of delay gates further comprises an even number plurality of delay gates.

3. The ring oscillator according to claim 2 wherein the even number plurality of delay gates further comprises one of two (2), four (4), eight (8), and sixteen (16) delay gates.

4. The ring oscillator according to claim 1 wherein the common circuit type is a NAND gate circuit type.

5. (canceled)

6. The ring oscillator according to claim 1 wherein the first plurality of delay gates is configured in electrical communication and in series.

7. The ring oscillator according to claim 4 wherein at least one of the first plurality of delay gates is further configured to transmit an output signal both to a subsequent NAND gate in the delayed circuit path and to a dummy NAND gate in the delayed circuit path.

8. The ring oscillator according to claim 1 wherein the multiplexer is of a 2-to-1 type.

9. A ring oscillator comprising a plurality of nested delay stages each comprising: a delay element comprising a first plurality of delay gates each of a common circuit type characterized by a common propagation delay t1 and a common capacitance C1, and a multiplexer comprising a second plurality of delay gates each of the common circuit type and including a first input gate, a second input gate, an output gate, and a selection line, wherein the delay element is positioned in a delayed circuit path defined between the first input gate and the output gate of the multiplexer, wherein the selection line is operable to switch, at an oscillation frequency f, an input signal between the delayed circuit path and a non-delayed circuit path defined between the second input gate and the output gate of the multiplexer, wherein a total capacitance C of the first and second pluralities of delay gates is proportional to a sum of the first plurality of delay gates and of the second plurality of delay gates, defining a delay gate count N, and the oscillation frequency f is inversely proportional to the delay gate count N, and wherein each of the first plurality of delay gates and of the second plurality of delay gates is characterized by a common capacitance-to-propagation delay ratio C1/t1; and wherein the plurality of nested delay stages is configured in electrical communication and in series such that a system output signal of a last-in-series of the plurality of nested delay stages is fed back into a first-in-series of the plurality of nested delay stages.

10. The ring oscillator according to claim 9 wherein the first plurality of delay gates further comprises an even number plurality of delay gates.

11. The ring oscillator according to claim 10 wherein the even number plurality of delay gates further comprises one of two (2), four (4), eight (8), and sixteen (16) delay gates.

12. The ring oscillator according to claim 9 wherein the common circuit type is a NAND gate circuit type.

13. The ring oscillator according to claim 12 wherein both the delayed circuit path and the non-delayed circuit path further comprise a respective dummy NAND gate, and each of the delayed circuit path and the non-delayed circuit path is configured to transmit a respective output signal to the respective dummy NAND gate and to the output gate.

14. (canceled)

15. The ring oscillator according to claim 9 wherein the first plurality of delay gates is configured in electrical communication and in series.

16. The ring oscillator according to claim 9 wherein the multiplexer is of a 2-to-1 type.

17. A method of manufacturing a ring oscillator, comprising the steps of: determining a required oscillation frequency f; determining a plurality N of delay gates each of a common circuit type characterized by a common propagation delay t1 and a common capacitance C1 and by a common capacitance-to-propagation delay ratio C1/t1, wherein a total capacitance C of the plurality N of delay gates is proportional to N and wherein the required oscillation frequency fis inversely proportional to N; assembling a delay element comprising a first subset of the plurality N of delay gates; and assembling a multiplexer comprising a second subset of the plurality N of delay gates including a selection line and a first input gate, a second input gate, and an output gate, by: positioning the delay element in a delayed circuit path defined between the first input gate and the output gate of the multiplexer, positioning a non-delayed circuit path defined between the second input gate and the output gate of the multiplexer, and operably configuring the selection line to switch, at the required oscillation frequency f, an input signal between the delayed circuit path and the non-delayed circuit path.

18. The method according to claim 17 wherein the plurality N of delay gates further comprise an even number plurality N of delay gates.

19. The method according to claim 17 wherein the common circuit type is a NAND gate circuit type.

20. The method according to claim 19 wherein assembling the delay element further comprises: positioning the first subset of the plurality N of delay gates in electrical communication and in series.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The preferred embodiments of the invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the invention, where like designations denote like elements, and in which:

[0023] FIG. 1 is a circuit diagram of an exemplary pure digital gated ring oscillator with adjustable frequency according to the prior art;

[0024] FIG. 2A is a circuit diagram of an exemplary delay element of FIG. 1;

[0025] FIG. 2B is a circuit diagram of an exemplary NAND gate implementation of the delay element of FIG. 2A;

[0026] FIG. 3 is a circuit diagram of a delay stage according to an embodiment of the present invention;

[0027] FIG. 4A is a circuit diagram of an exemplary NAND gate implementation of a delay element of the delay stage of FIG. 3;

[0028] FIG. 4B is a circuit diagram of an exemplary NAND gate implementation of a delay element of the delay stage of FIG. 3;

[0029] FIG. 5A is an exemplary pure digital gated ring oscillator with adjustable frequency according to an embodiment of the present invention; and

[0030] FIG. 5B is an exemplary pure digital gated ring oscillator with adjustable frequency according to an embodiment of the present invention.

[0031] Like reference numerals refer to like parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0033] Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.

[0034] As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims.

[0035] Furthermore, in this detailed description, a person skilled in the art should note that quantitative qualifying terms such as “generally,” “substantially,” “mostly,” and other terms are used, in general, to mean that the referred to object, characteristic, or quality constitutes a majority of the subject of the reference. The meaning of any of these terms is dependent upon the context within which it is used, and the meaning may be expressly modified.

[0036] Referring initially to FIGS. 3, 4A, 4B, 5A, and 5B, a gated ring oscillator with constant dynamic power consumption according to an embodiment of the present invention is now described in detail. Throughout this disclosure, the present invention may be referred to as a gated ring oscillator, a GRO, a ring oscillator, an oscillator device, an oscillator circuit, an oscillator, a circuit, an assembly, a device, a system, a product, and/or a method. Those skilled in the art will appreciate that this terminology is only illustrative and does not affect the scope of the invention. For instance, the present invention may just as easily relate to integrated circuit implementations characterized by frequency oscillation.

[0037] In general, the present invention relates to a pure digital ring oscillator circuit design characterized by constant power consumption when oscillation frequency is changed. The oscillator circuit topography of the present design may advantageously consume no static current and, therefore, save power; as well as advantageously ensure power consumption may not increase when the oscillation frequency is adjusted higher, which helps avoid complexity on the internal power rail of an integrated circuit.

[0038] The power consumption characteristics of known ring oscillator designs (such as that illustrated in FIG. 1 and described above) will now be described in more detail as a baseline for comparison. Generally speaking, known designs employ delay elements and multiplexing to change total length of a delay line, with selection logic (also referred to herein as a “selection line” and/or a “switch”) present at the multiplexer inserted after the delay elements along an electrical current path (also referred to herein as a “circuit path”). Referring more specifically to the circuit diagrams 200, 202 of FIGS. 2A. and 2B, respectively, a variable delay segment 122 is shown positioned upstream of a multiplexer 120 (e.g., “upstream” meaning between an electronic signal entering the system 200, 202 and the multiplexer 120). (The multiplexer 120 may be implemented using NAND gates 210, 220, 240 as shown in FIG. 2B).

[0039] In the prior art implementations shown in FIGS. 2A and 2B, selective inclusion or exclusion of the delay element 122 in the circuit path through the multiplexer 120 may be controlled by setting the logic level of a selection line B4 124. More specifically, as illustrated in FIG. 2B, the input B4 124 of a simple 2-1 line multiplexer circuit 202 constructed from NAND gates 210, 220, 240 acts to control which input (I0 212 or I1 222) gets passed to the output gate 240. When the data select input B4 124 is low (that is, input A1 214 is at logic 0 and input A2 is at logic 1 after inversion 230), input I1 222 may pass its signal through the NAND gate 220 to the output gate 240, while input I0 212 is blocked at NAND gate 210. When the data select input B4 124 is high (that is, input A1 214 is at logic 1 and input A2 224 is at logic 0 after inversion 230), input I0 212 may pass its signal through the NAND gate 210 to the output gate 240, while input I1 222 is blocked at NAND gate 220.

[0040] Accordingly, by application of either a logic 0 or a logic 1 at selection line B4 124, the appropriate input, I0 212 or I1 222, may be selected with the circuit 202 acting like a single pole double throw (SPDT) switch. However, a person of skill in the art will immediately recognize that, per the circuit topology designs illustrated in FIGS. 2A and 2B, all transistors in the delay element 122 will toggle on and off no matter which circuit path (e.g., I0 212 or I1 222) is activated (e.g., by input A1 214 or A2 224) using the selection line B4 124, resulting in power consumption dependency on oscillation frequency.

[0041] For example, and without limitation, the dynamic power consumption of a CMOS functional block may be calculated as follows:

P=C*(V.sup.2)*f

where V is the power supply voltage, C is the total capacitance (essentially contributed by the gates of the CMOS transistors) of the circuit nodes that flip at frequency f. If the total capacitance C in the ring oscillator may be designed to be proportional to the total number of equivalent delay cells N and each cell contributes a capacitance C1, the resultant model is as follows:

C=C1*N

[0042] Because the oscillation frequency f of the ring oscillator is inversely proportional to N, the dependence of the power consumption on N may be canceled, as follows:

P=(C1*N)*(V.sup.2)*(1/(2*t1*N))=(C1/(2*t1))*(V.sup.2)

where t1 is the unit time (i.e., propagation) delay contributed by each of the N delay cells.

[0043] Therefore, to ensure power consumption stays constant while changing the oscillation frequency, two design requirements must be satisfied: first, to employ a circuit topology such that C and f are proportional and inversely proportional to N, respectively; and, second, to select all logic elements in the ring oscillator to have an identical ratio of the capacitance and propagation delay (C1/t1).

[0044] Referring now to FIG. 3, the gated ring oscillator circuit topology 300 (also referred to herein as a “delay stage”) of the present invention may differ, for example, and without limitation, from the prior art circuit design 202 shown in FIG. 2B at least in that the delay element 322 may be placed after a path selection NAND gate 310 (i.e., downstream of NAND gate 310 in relation to a unidirectional current flow input to the circuit 300 from a direct current (DC) source (not shown)) of a multiplexer comprising NAND gates 310, 320, and 340. In the circuit design 300, as shown, transistors in the delay element 322 advantageously may not toggle if the shorter signal path (e.g., through NAND gate 320 to NAND gate 340 of circuit 300) is chosen using selection line B4 324.

[0045] In certain embodiments of the present invention, the delay element(s) may be built using the same type of NAND gates as those used in the multiplexer implementation. As shown in FIG. 4A, for example, and without limitation, the delay element 322(a) may comprise NAND gates 410, 420, 430, and 440 electrically connected in series to define a circuit path, and with one input of each of the NAND gates connected to logic 1 (as exemplified at 402). Also for example, and without limitation, because the output signal of an input NAND gate of a multiplexer may drive two loads of inputs to output NAND gates positioned subsequent in the circuit 322(b), dummy NAND gates 412, 422, 432, 442 (as shown in FIG. 4B marked with dashed line) may be optionally added so that all active NAND gates 410, 420, 430, 440 in the circuit 322(b) may drive two loads for uniformed performance without complicating calculations on the gate transistor aspect ratios.

[0046] Referring now to FIGS. 5A and 5B, exemplary embodiments of pure digital gated ring oscillators 500, 599 characterized by constant dynamic power consumption are shown in detail. Because the delay elements 510, 322, 530, 540 and their respective complementary multiplexers (collectively referred to as nested delay stages 502, 300, 508, and 516) may be built using identical NAND gates as described above for FIGS. 4A, 4B, all elements in the ring loops of FIGS. 5A, 5B may exhibit the same propagation delay and transistor gate capacitance. Therefore, and advantageously, the power consumption of the ring oscillator of the present design may be constant while the oscillation frequency is adjusted using any included multiplexer's selection lines 514, 324, 534, 544. Referring more specifically to FIG. 5B, optional dummy NAND gates 512, 522, 532, 542, 552, 562, 572, 582 (drawn in dashed line) may be configured to allow active input NAND gates in the circuit 599 to each drive two loads for uniformed performance without complicating calculations on the gate transistor aspect ratios. As shown in FIGS. 5A and 5B, and as described above, a ring oscillator circuit topology that comprises any number of multiplexers implemented in NAND gates with respective delay elements positioned after a path selection NAND gate of the multiplexer may advantageously not toggle the transistors in the delaying signal path when the non-delaying signal path is selected.

[0047] Some of the illustrative aspects of the present invention may be advantageous in solving the problems herein described and other problems not discussed which are discoverable by a skilled artisan.

[0048] While the above description contains much specificity, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presented embodiments thereof. Many other ramifications and variations are possible within the teachings of the various embodiments. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0049] Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.