# Patent

## Title
Leakage efficient anti-glitch filter

## Abstract

A leakage efficient anti-glitch filter. In accordance with a first embodiment of the present invention, a leakage efficient anti-glitch filter comprises a delay element and a coincidence detector element for detecting coincidence of an input signal to the delay element and an output of the delay element. The delay elements may comprise stacked inverter circuits or stacked NAND gates.

## Background
RELATED APPLICATIONS
This application is a Continuation-in-Part of co-pending, commonly owned U.S. patent application Ser. No. 10/864,271, filed Jun. 8, 2004, entitled “Stacked Inverter Delay Chain” to Masleid and Burr, which is hereby incorporated herein by reference in its entirety.
This application is related to the following co-pending, commonly assigned United States patent applications, which are hereby incorporated herein by reference in their entirety:
U.S. patent application Ser. No. 11/021,222, filed Dec. 23, 2004, entitled “A Configurable Tapered Delay Chain with Multiple Sizes of Delay Elements” by Masleid;
U.S. patent application Ser. No. 11/021,221, filed Dec. 23, 2004, entitled “A Configurable Delay Chain with Switching Control for Tail Delay Elements” by Masleid;
U.S. patent application Ser. No. 11/021,632, filed Dec. 23, 2004, entitled “Power Efficient Multiplexer” to Masleid;
U.S. patent application Ser. No. 11/021,197, filed Dec. 23, 2004, entitled “Leakage Efficient Anti-glitch Filter with Variable Delay Stages” by Masleid;
U.S. patent application Ser. No. 11/020,746, filed Dec. 23, 2004, entitled “A Configurable Delay Chain with Stacked Inverter Delay Elements” by Masleid; and


FIELD OF THE INVENTION
Embodiments in accordance with the present invention relate to leakage efficient anti-glitch filters.
BACKGROUND
It is sometimes advantageous to delay propagation of a signal through an integrated circuit. A common approach to create such signal delays is to insert a delay circuit, or delay “line,” into a signal path. One well known class of delay circuits is a variable delay circuit. For example, a variable delay circuit can function by selectably varying a number of delay elements to produce different amounts of delay to a signal propagating through such elements. However, in general, variable delay lines can generate “glitches” or deleterious spurious signals. For example, changing a delay duration while a transition is propagating through the delay line can sometimes cause the transition to arrive twice at the output, producing a glitch. Further, it is generally desirable for delay circuit designs to be efficient in terms of integrated circuit die area, active power consumption and static power (leakage current) consumption.
SUMMARY OF THE INVENTION
A leakage efficient anti-glitch filter is disclosed. In accordance with a first embodiment of the present invention, a leakage efficient anti-glitch filter comprises a delay element and a coincidence detector element for detecting coincidence of an input signal to the delay element and an output of the delay element. The delay elements may comprise stacked inverter circuits or stacked NAND gates.
In accordance with another embodiment of the present invention, a method of filtering glitches from an electronic signal is disclosed. An electronic signal is accessed. A delayed version of the electronic signal is produced. The electronic signal and the delayed version of the electronic signal are combined to produce a glitch-free electronic signal. The glitch-free electronic signal transitions in response to a coincidence of the electronic signal and the delayed version of the electronic signal.
In accordance with still another embodiment of the present invention, an electronic circuit is disclosed. The electronic circuit comprises a delay line comprising a plurality of stacked inverters coupled in series. Each of the plurality of stacked inverters comprises at least two devices of a first type coupled in series, coupled in series to at least two devices of an opposite type coupled in series. The electronic circuit further comprises a coincidence detector circuit. The coincidence detector circuit comprises first and second devices of a first type coupled in series, coupled in series to third and fourth devices of a second type coupled in series. An input to the delay line is coupled to gates of the first and fourth devices and an output of the delay line is coupled to gates of the second and third devices.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic of a novel leakage efficient anti-glitch filter, in accordance with embodiments of the present invention.
FIG. 2 is a timing diagram illustrating a function of a leakage efficient anti-glitch filter, in accordance with embodiments of the present invention.
FIG. 3 illustrates a flow chart describing a method of filtering glitches from an electronic signal, in accordance with embodiments of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
In the following detailed description of the present invention, leakage efficient anti-glitch filter with variable delay stages, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one skilled in the art that the present invention may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.
Leakage Efficient Anti-Glitch Filter
Embodiments in accordance with the present invention are described in the context of design and operation of integrated semiconductors. More particularly, embodiments of the present invention relate to leakage efficient anti-glitch filters. It is appreciated, however, that elements of the present invention may be utilized in other areas of semiconductor design and operation.
The following description of embodiments in accordance with the present invention is directed toward pFETs (or p-type metal oxide semiconductor field effect transistors (MOSFETS)) formed in surface N-wells and/or nFETs (or n-type MOSFETS) formed in surface P-wells when a p-type substrate and an N-well process are utilized. It is to be appreciated, however, that embodiments in accordance with the present invention are equally applicable to nFETs (or n-type MOSFETS) formed in surface P-wells and/or pFETs (or p-type MOSFETS) formed in surface N-wells when an n-type substrate and a P-well process are utilized. Consequently, embodiments in accordance with the present invention are well suited to semiconductors formed in both p-type and n-type materials, and such embodiments are considered within the scope of the present invention.
FIG. 1 illustrates a schematic of a novel leakage efficient anti-glitch filter 100, in accordance with embodiments of the present invention. Leakage efficient anti-glitch filter 100 comprises an optional input buffer 110, a leakage efficient delay line 120 and a coincidence detector element 130.
Optional input buffer 110 can provide transition speed isolation. For example, without optional input buffer 110, leakage efficient delay line 120 presents six loads at its input. Such loading may represent an undesirable loading condition to the source of a signal. In accordance with embodiments of the present invention, input buffer 110 is well suited to a variety of buffering structures, including, for example, conventional or stacked inverters and non-inverting buffers.
It is to be appreciated that static power consumption in modern semiconductor processes, e.g., processes with a minimum feature size of about 0.13 microns and smaller, is no longer a negligible component of total power consumption. For such processes, static power may be one-half of total power consumption. Further, static power, as a percentage of total power, is tending to increase with successive generations of semiconductor process.
Embodiments in accordance with the present invention offer significant advantages in reducing leakage current, or static power consumption, in comparison with the conventional art. In general, an inverter stage, whether conventional or stacked, forms a leakage path, e.g., a series “string” of devices coupled from operating voltage (Vdd) to ground. As current leaks out of such leakage paths, static power is consumed by the inverter stage. As described more completely in U.S. patent application Ser. No. 10/864,271, entitled “Stacked Inverter Delay Chain” to Masleid and Burr, incorporated herein by reference in its entirety, a delay chain comprising stacked inverters can require fewer stages than a delay chain comprising conventional inverters to produce a comparable delay. For example, each stage of stacked inverters will generally produce greater delay than a conventional, non-stacked inverter. Fewer stages result in fewer leakage paths, resulting in advantageously less leakage current, resulting in less static power consumption.
Further, such leakage paths within a stacked inverter suffer less leakage than a conventional inverter, yielding additional beneficial leakage reductions. In a conventional inverter, exactly one transistor is on while the other transistor is off. As an unfortunate consequence, approximately the full bias voltage is applied to the off transistor, resulting in a maximum possible leakage for the off transistor.
In contrast, in a stacked inverter multiple transistors are either on or off in series. For example, in the embodiment of FIG. 1, for a “high” state, two transistors are on, while two transistors are off. Consequently, each “off” transistor has significantly less than full bias voltage applied. It is appreciated that leakage current generally decreases exponentially as voltage decreases. For example, a factor of two reduction in off bias voltage produces about a factor of eight reduction in leakage current per leakage path.
It is to be further appreciated that such leakage induces non zero voltages at intermediate nodes between the off transistors. Such voltages induce body effects in the transistors. Such body effects increase the threshold voltage of the affected transistors. An increased threshold voltage generally produces beneficial decreases in leakage current.
Consequently, in addition to a decrease in a number of leakage paths, in accordance with embodiments of the present invention, the leakage current of each path is very beneficially reduced due to an induced body effect and a highly non-linear relationship between bias voltage and leakage current. Thus, leakage efficient delay line 120 significantly reduces static power consumption, in comparison to a delay line comprising conventional inverters.
Leakage efficient delay line 120 comprises a plurality of stacked inverters. The output of a first stacked inverter is generally coupled to the input of a subsequent stacked inverter. It is to be appreciated that more or fewer stacked inverters can be included in leakage efficient delay line 120 in order to achieve differing signal delay values, in accordance with embodiments of the present invention.
For example, physical differences between electrons and holes, and between n-type and p-type dopants, as well as constructive differences in device geometry and dopant placement, result in differences in efficiency between n-type devices and p-type devices. Because electron mobility is higher than hole mobility, n-type devices are more efficient than p-type devices. However, the degree of difference depends on constructive differences that can vary with process. Such physical and constructive differences also produce other behavior differences, such as a difference in sensitivity to body effects. Consequently, different levels of benefit, e.g., in leakage reduction, are to be expected between stacks of n-type devices and stacks of p-type devices. To allow for such effects, in accordance with embodiments of the present invention, it is possible to stack different numbers of transistors on either or both legs of a stacked inverter. Such variations allow increases in load and/or decreases in drive capability, enabling a wide variety of delay values, as well as enabling differing body effects.
In contrast to a conventional inverter, the stacked inverters of leakage efficient delay line 120 comprise more than a single p-type device coupled to a single n-type device. Rather, the stacked inverters of leakage efficient delay line 120 comprise multiple p-type devices and multiple n-type devices. In the embodiment of FIG. 1, the inverters are shown as comprising two p-type devices and two n-type devices. It is appreciated that embodiments of the present invention are well suited to a variety of stacking combinations of p-type and n-type devices, as well as to other delay elements, for example leakage efficient, e.g., stacked, NAND gates.
As will be discussed further below, the signal delay produced by leakage efficient delay line 120 is related to the duration of spurious signals, or glitches, that are to be filtered by leakage efficient anti-glitch filter 100.
Still referring to FIG. 1, coincidence detector element 130 functions to combine signal A 111, the input of leakage efficient delay line 120, with signal B 121, the output of leakage efficient delay line 120. Coincidence detector element 130 will only propagate a signal when signals A 111 and B 121 coincide.
In the embodiment of FIG. 1, coincidence detector element 130 comprises a “Mueller-C” element. It is appreciated that embodiments of the present invention are well suited to other types of coincidence detectors. A Mueller-C element is a well known special type of NAND gate characterized by propagating a state change only when both of its inputs agree. For example, a true NAND (or AND) gate can transition from true to false when only one of its inputs changes from true to false. In contrast, coincidence detector element 130 does not transition until all inputs agree, e.g., both inputs change from true to false.
For example, only when both signal A 111 and signal B 121 are low will the pFET devices of coincidence detector element 130 turn on and pull output signal C 131 to a high condition. Similarly, only when both signal A 111 and signal B 121 are high will the nFET devices of coincidence detector element 130 turn on and pull output C 131 to a low condition.
Conventionally, coincidence detector elements, e.g., a Mueller-C element, are generally utilized to compare or combine disparate signals. For example, a conventional use of such elements is to determine completion of a logic function.
In contrast, in accordance with embodiments of the present invention, coincidence detector element 130 receives as input the input to leakage efficient delay line 120 and the output of leakage efficient delay line 120. Thus, coincidence detector element 130 receives a signal and a delayed version of the same signal.
Leakage efficient anti-glitch filter 100 suppresses any glitch or spurious signal characterized as having a duration of less than the delay characteristic of leakage efficient delay line 120.
It is generally desirable for a delay circuit, e.g., leakage efficient delay line 120, to track speed changes of other circuitry of an integrated circuit. It is appreciated that a variety of factors, e.g., operating voltage, operating temperature and/or manufacturing process variations, can affect the speed of operation of an integrated circuit. For example, if other circuits of an integrated circuit operate faster, generally less absolute delay is required from a delay circuit for the overall circuit to function. By way of further example, if other circuits of an integrated circuit operate more slowly, it may be advantageous for leakage efficient delay line 120 to operate more slowly, e.g., with greater absolute delay, in order to remove longer glitches generated by such slower operating other circuitry. Because embodiments in accordance with the present invention comprise stacked devices, they are similar to many logic circuits that also comprise stacked devices, e.g., NAND and/or NOR logic gates. Consequently, embodiments in accordance with the present invention match or track changes in operating speed of complex logic more accurately than delay chains comprising very simple inverters.
Embodiments in accordance with the present invention are thus shown to offer significant and highly beneficial improvements in tracking timing changes of other circuits and in static power (leakage current) consumption in comparison to the conventional art.
FIG. 2 is a timing diagram 200 illustrating a function of leakage efficient anti-glitch filter 100, in accordance with embodiments of the present invention. Timing diagram 200 shows a relationship among exemplary signals associated with leakage efficient anti-glitch filter 100.
Signal A 210 is an input waveform to leakage efficient anti-glitch filter 100. Signal A 210 is one possible signal corresponding to signal A 111 of FIG. 1. Signal A 210 comprises a glitch 220 and a desired transition 230.
Signal B 240 is a delayed version of signal A 210, corresponding to the output B 121 of leakage efficient delay line 120 (FIG. 1). Signal B 240 is a reproduction of signal A 210, delayed by a duration 245. It is to be appreciated that duration 245 corresponds to the delay of leakage efficient delay line 120 of FIG. 1. Signal B 240 comprises a glitch 250, corresponding to glitch 220, and a desired transition 260, corresponding to desired transition 230. It is to be appreciated that glitch 250 and desired transition 260 are delayed by duration 245 in relation to their corresponding elements of signal A 210. It is to be further appreciated that glitch 220 is of a time duration that is less than delay duration 245.
Signal C 270 is an output of leakage efficient delay line 120 as viewed at output C 131 (FIG. 1) when excited by signal A 210. It is appreciated that desired transition 280 of signal C 270 does not occur until both signal A 210 and signal B 240 agree. For example, at a time before desired transition 280, signal B 240 is low. Consequently, changes in signal A 210, e.g., glitch 220 and/or desired transition 230, do not affect signal C 270.
At the time of desired transition 280, signal A 210 is high, and signal B 240 transitions to high. Consequently, signal C 270 transitions to low, producing desired transition 280. As signal A 210 is high for the remaining duration of timing diagram 200, changes in signal B 240, e.g., glitch 250 and/or desired transition 260, do not affect signal C 270.
Thus, in accordance with embodiments of the present invention, a spurious signal, e.g., glitch 220, present on an input to leakage efficient anti-glitch filter 100 (FIG. 1) is removed, and is not present on the output of leakage efficient anti-glitch filter 100.
It is to be appreciated that signal C 270 is inverted relative to signal A 210. Referring once again to FIG. 1, the output of leakage efficient anti-glitch filter 100, e.g., signal C 131, can be inverted by an inverting circuit (not shown) to obtain a positive phase relationship to a signal input to leakage efficient anti-glitch filter 100. Alternatively, an inverting optional input buffer 110 can “pre-invert” a signal input to leakage efficient anti-glitch filter 100 in order to obtain a positive phase relationship between an input signal and an output signal.
FIG. 3 illustrates a flow chart describing a method 300 of filtering glitches from an electronic signal, in accordance with embodiments of the present invention. In 310, an electronic signal is accessed. For example, referring once again to FIG. 1, signal A 111 is accessed by leakage efficient anti-glitch filter 100.
In 320, a delayed version of the electronic signal is produced. For example, signal B 121 is a delayed version of signal A 111 in FIG. 1. In 330, the electronic signal and the delayed version of the electronic signal are combined to produce a glitch-free electronic signal. The glitch-free electronic signal transitions in response to a coincidence of the electronic signal and the delayed version of the electronic signal.
Embodiments in accordance with the present invention thus provide a leakage efficient anti-glitch filter comprising desirable static power (leakage current) consumption in comparison to the conventional art.
Embodiments in accordance with the present invention, leakage efficient anti-glitch filter, are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims.

## Claims

1. An anti-glitch filter circuit comprising:
a delay element,
wherein said delay element is formed by serially connecting stacked inverters in multiple stages; and

a coincidence detector element operable to detect coincidence of an input signal to said delay element and an output signal of said delay element,
wherein said delay element and said coincidence detector substantially eliminate spurious signals of said input signal when said spurious signals have a duration less than a delay generated by said stacked inverters in multiple stages.

2. The anti-glitch filter circuit of claim 1 wherein said delay is configured based on said stacked inverters.

3. The anti-glitch filter circuit of claim 2 wherein said coincidence detector comprises a Mueller-C element.

4. The anti-glitch filter circuit of claim 3 wherein each one of said stacked inverters comprises at least two p-type devices coupled in series with at least two n-type devices.

5. The anti-glitch filter circuit of claim 4 wherein said each one of said stacked inverters is characterized in having a greater switching time duration than an inversion performed by an inverter comprising only two active devices.

6. The anti-glitch circuit of claim 5 wherein said each one of said stacked inverters is characterized in having less leakage than said inverter comprising only two active devices.

7. The anti-glitch filter circuit of claim 4 wherein said each one of said stacked inverters comprises:
a first plurality of devices of a first type coupled in series;
a second plurality of devices of a second type coupled in series,
wherein said second type is opposite to said first type; and
wherein said first and second pluralities of devices are coupled in series and comprise at least five active devices.

8. A method of filtering glitches from an electronic signal comprising:
accessing an electronic signal;
producing a delayed version of said electronic signal by processing said electronic signal through a delay element formed by serially connecting stacked inverters in multiple stages; and
combining said electronic signal and said delayed version of said electronic signal to produce a glitch-free electronic signal, wherein said glitch-free electronic signal transitions in response to a coincidence of said electronic signal and said delayed version of said electronic signal.

9. The method of claim 8 wherein said combining comprises filtering glitches characterized as having a duration of less than a delay of said delayed version of said electronic signal.

10. Said method of claim 9 further comprising changing a number of said stacked inverters in multiple stages to finely adjust said delay.

11. Said method of claim 10 wherein said changing said number of said stacked inverters further comprises changing a number of active devices in each one of said stacked inverters in multiple stages.

12. Said method of claim 11 wherein said changing said number of said stacked inverters further comprises selecting a combination of n-type devices and p-type devices in said each one of said stacked inverters in multiple stages.

13. Said method of claim 11 further comprising adjusting said number of said stacked inverters in multiple stages and said number of active devices in each one of said stacked inverters to substantially decrease a leakage current in said delay element while substantially maintaining said delay.

14. The method of claim 8 wherein said combining is performed using a Muller-C element.

15. The method of claim 14 wherein each one of said stacked inverters comprises at least two p-type devices coupled in series with at least two n-type devices.

16. The method of claim 15 wherein said each one of said stacked inverters is characterized in having a greater switching time duration than an inversion performed by an inverter comprising only two active devices.

17. The method of claim 16 wherein said each one of said stacked inverters is characterized in having less leakage current than said inverter comprising only two active devices.

18. The method of claim 15 wherein said each one of said stacked inverters comprises:
a first plurality of devices of a first type coupled in series; and
a second plurality of devices of a second type coupled in series,
wherein said second type is opposite to said first type; and
wherein said first and said second pluralities of devices are coupled in series and comprise at least five active devices.

19. An electronic circuit comprising:
a delay line comprising a plurality of stacked inverters coupled in series, each of said plurality of stacked inverters comprising:
at least two devices of a first type coupled in series, serially coupled to
at least two devices of a second type coupled in series,
wherein said second type is opposite to said first type; and
wherein a delay is generated by said stacked inverters, and


a coincidence detector circuit comprising:
first and second devices of a first type coupled in series, serially coupled to
third and fourth devices of a second type couple in series;
wherein an input to said delay line is coupled to gates of said first and fourth devices and an output of said delay line is coupled to gates of said second and third devices.

20. The electronic circuit of claim 19 wherein gates of each device comprising each of said plurality of stacked inverters are coupled together.

21. The electronic circuit of claim 19 wherein each of said plurality of stacked inverters are substantially identical.

22. The electronic circuit of claim 19 wherein each of said plurality of stacked inverters comprises two p-type devices.

23. The electronic circuit of claim 19 wherein each of said plurality of stacked inverters comprises three n-type devices.

24. The electronic circuit of claim 19 further comprising an inverter coupled to said input of said delay line.