# Patent

## Title
Digital technique for excess loop delay compensation in a continuous-time delta sigma modulator

## Abstract

A continuous time delta sigma modulator includes a quantizer and a reference module. The quantizer includes: a first comparator that generates a first digital output based on a comparison of a first reference potential with an input generated based on a sample of an analog signal; and a second comparator that generates a second digital output based on a comparison of a second reference potential with the input generated based on the sample of the analog signal. The reference module varies the first and second reference potentials based on the first and second digital outputs.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 62/039,647 filed on Aug. 20, 2014. The entire disclosure of the application referenced above is incorporated herein by reference.


FIELD
The present disclosure relates to analog to digital converters and more particularly to systems and methods for minimizing excess loop delay of continuous time delta sigma modulators.
BACKGROUND
The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Analog-to-digital converters (ADCs) convert samples of an analog input signal into digital values corresponding to the samples. Various types of ADCs are available, such as successive-approximation-register (SAR) ADCs, Delta-Sigma (As) ADCs, and pipelined ADCs. ADCs may be used in various electronic devices, such as finite impulse resolution (FIR) digital to analog converters (DACs) and many other types of electronic devices.
SUMMARY
In a feature, a continuous time delta sigma modulator is disclosed. A quantizer includes: a first comparator that generates a first digital output based on a comparison of a first reference potential with an input generated based on a sample of an analog signal; and a second comparator that generates a second digital output based on a comparison of a second reference potential with the input generated based on the sample of the analog signal. A reference module varies the first and second reference potentials based on the first and second digital outputs.
In further features, a buffer module receives the first and second digital outputs, delays outputting the first and second digital outputs for less than one cycle of a clock signal, and outputs the delayed first and second digital outputs to the reference module. The reference module varies the first and second reference potentials based on the delayed first and second digital outputs, and the first and second comparators update the first and second digital outputs each cycle of the clock signal.
In further features, the buffer module delays outputting the first and second digital outputs for one-half of the cycle of the clock signal.
In further features, the reference module includes: a switching module that includes a plurality of switching devices and a plurality of resistors that regulate the first and second reference potentials; and a switch control module that controls states of the switching devices based on the delayed first and second digital outputs.
In further features, the switch control module includes: at least one thermometer to binary encoder that encodes the delayed first and second digital outputs to produce encoded outputs; and at least one logic gate that performs a digital logic function based on the encoded outputs to produce at least one switching signal and that applies the at least one switching signal to one or more of the switching devices of the switching module.
In further features, the switch control module includes: a first thermometer to binary encoder that generates first and second encoded outputs based on the delayed first and second digital outputs; a second thermometer to binary encoder that generates third and fourth encoded outputs based on the delayed first and second digital outputs; a first AND gate that generates a first switching signal based on a logical AND function of the first and second encoded outputs and that applies the first switching signal to a first set of one or more of the switching devices; a second AND gate that generates a second switching signal based on a logical AND function of the first and third encoded outputs and that applies the second switching signal to a second set of one or more of the switching devices; a third AND gate that generates a third switching signal based on a logical AND function of the second and third encoded outputs and that applies the third switching signal to a third set of one or more of the switching devices; and a fourth AND gate that generates a fourth switching signal based on a logical AND function of the third and fourth encoded outputs and that applies the fourth switching signal to a fourth set of one or more of the switching devices.
In further features: a digital to analog converter (DAC) converts the delayed first and second digital outputs into an analog value; and an integrator generates the input based on the sample of the analog signal and the analog value.
In further features: a subtractor subtracts the analog value from the sample of the analog signal to produce an output, and the integrator generates the input based on an integral of the output of the subtractor.
In further features: the quantizer further includes N additional comparators that generate N additional digital outputs based on comparisons of N additional reference potentials, respectively, with the input generated based on the sample of the analog signal, N is an integer greater than zero; and the reference module varies the first reference potential, the second reference potential, and the N additional reference potential based on the first digital output, the second digital output, and the N additional digital outputs.
In further features, the reference module includes: a switching module that includes a plurality of switching devices and a plurality of resistors that regulate the first reference potential, the second reference potential, and the N additional reference potentials; and a switch control module that controls states of the switching devices based on the first digital output, the second digital output, and the N additional digital outputs.
In a feature, a method includes: using a first comparator of a quantizer of a continuous time delta sigma modulator, generating a first digital output based on a comparison of a first reference potential with an input generated based on a sample of an analog signal; using a second comparator of the quantizer of the continuous time delta sigma modulator, generating a second digital output based on a comparison of a second reference potential with the input generated based on the sample of the analog signal; and varying the first and second reference potentials based on the first and second digital outputs.
In further features, the method further includes: using a buffer module of the continuous time delta sigma modulator, receiving the first and second digital outputs, delaying outputting the first and second digital outputs for less than one cycle of a clock signal, and outputting the delayed first and second digital outputs; varying the first and second reference potentials based on the delayed first and second digital outputs; and using the first and second comparators, updating the first and second digital outputs each cycle of the clock signal.
In further features, the method further includes, using the buffer module, delaying outputting the first and second digital outputs for one-half of the cycle of the clock signal.
In further features, the method further includes: using a switching module that includes a plurality of switching devices and a plurality of resistors, regulating the first and second reference potentials; and controlling states of the switching devices based on the delayed first and second digital outputs.
In further features, the method further includes: using at least one thermometer to binary encoder, encoding the delayed first and second digital outputs to produce encoded outputs; and using at least one logic gate, performing a digital logic function based on the encoded outputs to produce at least one switching signal and applying the at least one switching signal to one or more of the switching devices of the switching module.
In further features, the method further includes: using a first thermometer to binary encoder, generating first and second encoded outputs based on the delayed first and second digital outputs; using a second thermometer to binary encoder, generating third and fourth encoded outputs based on the delayed first and second digital outputs; using a first AND gate, generating a first switching signal based on a logical AND function of the first and second encoded outputs and that applying the first switching signal to a first set of one or more of the switching devices; using a second AND gate, generating a second switching signal based on a logical AND function of the first and third encoded outputs and applying the second switching signal to a second set of one or more of the switching devices; using a third AND gate, generating a third switching signal based on a logical AND function of the second and third encoded outputs and applying the third switching signal to a third set of one or more of the switching devices; and using a fourth AND gate, generating a fourth switching signal based on a logical AND function of the third and fourth encoded outputs and applying the fourth switching signal to a fourth set of one or more of the switching devices.
In further features, the method further includes: using a digital to analog converter (DAC), converting the delayed first and second digital outputs into an analog value; and using an integrator, generating the input based on the sample of the analog signal and the analog value.
In further features, the method further includes: using a subtractor, subtracting the analog value from the sample of the analog signal to produce an output; and using the integrator, generating the input based on an integral of the output of the subtractor.
In further features, the method further includes: using N additional comparators of the quantizer of the continuous time delta sigma modulator, generating N additional digital outputs based on comparisons of N additional reference potentials, respectively, with the input generated based on the sample of the analog signal, wherein N is an integer greater than zero; and varying the first reference potential, the second reference potential, and the N additional reference potential based on the first digital output, the second digital output, and the N additional digital outputs.
In further features, the method further includes: using a switching module that includes a plurality of switching devices and a plurality of resistors, regulating the first reference potential, the second reference potential, and the N additional reference potentials; and controlling states of the switching devices based on the first digital output, the second digital output, and the N additional digital outputs.
Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.



BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a functional block diagram of an example delta sigma modulator;
FIG. 2 is an example graph illustrating impulse responses of the example delta sigma modulator of FIG. 1;
FIG. 3 is a functional block diagram of an example delta sigma modulator including components for compensating for excess loop delay;
FIG. 4 includes graphs illustrating example impulse responses of the example delta sigma modulator of FIG. 3;
FIG. 5 is a functional block diagram of an example delta sigma modulator including a reference module for compensating for excess loop delay;
FIG. 6 is an example schematic of a switching module of the reference module;
FIG. 7 is an example schematic of a switch control module of the reference module;
FIG. 8 is an example schematic of an example delta sigma modulator including the reference module;
FIG. 9 is a graph of example signal to quantization noise ratio (SQNR) of the example sigma delta modulator of FIG. 8;
FIG. 10 is a graph including an example power spectral density (PSD) of the example sigma delta modulator of FIG. 8; and
FIG. 11 is a flowchart depicting an example method that may be performed by a delta sigma modulator.



In the drawings, reference numbers may be reused to identify similar and/or identical elements.
DETAILED DESCRIPTION
A quantizer of a delta sigma modulator generates a digital representation of a sample of an analog signal via a conversion process. During the conversion process, the quantizer generates digital outputs based on comparisons of an input with a plurality of reference potentials. The input is generated based on the sample of the analog signal.
One or more digital to analog converters (DACs) convert the digital outputs to corresponding analog values, and the input to the quantizer is updated based on the analog values. The quantizer updates the digital outputs based on the updated input. The input and the digital outputs are updated on multiple occasions (based on a clock signal) between times when the analog signal is sampled. This enables the digital outputs to be adjusted during the conversion process to best represent the sample of the analog signal.
Continuous time delta sigma modulators generally suffer from Excess Loop Delay (ELD). The ELD of a delta sigma modulator may correspond to a delay period associated with the one or more DACs, a delay period of the components that provide the input to the quantizer, and a delay period of the quantizer itself. The delay period of the quantizer may correspond to a period between when the quantizer is prompted to update the digital outputs (e.g., based on the clock signal) and when the quantizer actually outputs the updated digital outputs. Relative to the delay period of the quantizer, the delay period of the DAC(s) and the delay period of the components that provide the input to the quantizer may be negligible.
The ELD of a delta sigma modulator can be reduced by providing an adder, an additional DAC, and one or more delay buffers. However, this may increase power consumption of the delta sigma modulator.
A delta sigma modulator according to the present disclosure includes a reference module that adjusts the reference potentials provided to the quantizer during the conversion process. As described above, the quantizer compares an input with the reference potentials to generate the digital outputs. Relative to the use of an adder and an additional DAC, adjusting the reference potentials decreases power consumption of the delta sigma modulator.
Referring now to FIG. 1, a functional block diagram of an example first-order continuous time delta sigma (ΔΣ) modulator is presented. The delta sigma modulator includes an adder 104, an integrator 108, a quantizer including a plurality of comparators 112, and a DAC 116. The DAC 116 generates an analog output (Y(t)) based on the digital outputs of the comparators 112.
The adder 104 includes a non-inverting input that receives a sample of an analog signal (UIN(t)) and an inverting input that receives the analog output of the DAC 116. The adder 104 subtracts the analog output of the DAC 116 from the sample of the analog signal. The integrator 108 integrates the output of the adder 104 and provides an integrated output (X1(t)) to the comparators 112. The analog signal is sampled each predetermined sampling period for digitization by the delta sigma modulator. When the conversion process is complete, the digital outputs of the comparators 112 are a digital representation of the sample of the analog input signal.
The comparators 112 compare the integrated output with respective references (Vref) at each clock period (Ts). In this case, the references are fixed. The comparators 112 generate the digital outputs based on the comparisons, respectively. The clock period (Ts) is shorter than the predetermined sampling period (of the analog input signal) so multiple sets of the digital outputs can be fed back for comparison with each sample of the analog input signal. FIG. 2 includes example graphs depicting example responses of the delta sigma modulator of FIG. 1 to the application of an impulse to the DAC 116.
Referring now to FIG. 3, a functional block diagram of an example first-order continuous time delta sigma modulator is presented. The example delta sigma modulator of FIG. 3 includes additional components for compensating for excess loop delay (ELD). However, the additional components are configured such that the input to the comparators 112 is the same in the example of FIG. 3 as the input to the comparators 112 in the example of FIG. 1.
A buffer module 204 buffers the digital outputs of the comparators 112 for one-half of the clock period (Ts) before outputting the (delayed) digital outputs. The DAC 116 generates the analog output based on the delayed digital outputs.
A second DAC 208 generates a second analog output based on the delayed digital outputs. A gain module 212 applies a gain (k) to the second analog output to produce a gain applied analog output (U2(t)). For example only, the gain may be 0.5 corresponding to the one-half clock period delay provided by the buffer module 204. While the example including a one-half clock period delay and a gain of 0.5 is shown and discussed, another suitable delay period and another suitable gain may be used.
A second adder 216 includes a non-inverting input that receives the integrated output of the integrator 108 (W(t) in the example of FIG. 3) and an inverting input that receives a negative value of the gain applied analog output. The second adder 216 subtracts the gain applied analog output from the integrated output. The comparators 112 compare the output of the second adder 216 (X2(t)) with the respective references (Vref) each predetermined clock period (Ts). As in the example of FIG. 1, the references are fixed values in the example of FIG. 3. The comparators 112 generate the digital outputs based on the comparisons, respectively.
FIG. 4 includes graphs depicting example responses of the delta sigma modulator of FIG. 3 to the application of an impulse to the buffer module 204. As can be seen by comparing FIGS. 2 and 4, the input to the comparators 112 (X2(t)) in the example of FIG. 3 resulting from the application of the impulse is the same as the input to the comparators 112 (X1(t)) in the example of FIG. 1 resulting from the application of the impulse.
The example of FIG. 3 reduces the quantizer delay to one half of the sampling period. However, the example of FIG. 3 includes the second DAC 208 and the second adder 216 and, therefore, has the associated additional power consumption.
FIG. 5 is a functional block diagram of an example third order continuous time sigma delta modulator having a two-bit quantizer. While the sample of a third order sigma delta modulator having a two-bit quantizer is shown and will be discussed, the present application is applicable to second and higher order sigma delta modulators including multiple-bit quantizers.
A transfer function (H(s)) corresponding to one or more integrators, feed-forward components, feed-back components, and other components implemented upstream of the comparators 112 are represented by transfer function block 402. The example delta sigma modulator of FIG. 5 includes a reference module 408 that varies the reference voltages supplied to the comparators 112.
The reference module 408 includes a switching module 412 (see also FIG. 7) and a switch control module 416 (see also FIG. 6). The switching module 412 includes a plurality of switching devices. The switch control module 416 controls the states of the switching devices of the switching module 412 based on the delayed digital outputs from the buffer module 204.
Based on the states of the switching devices, the switching module 412 outputs adjusted reference voltages ({circumflex over (V)}ref) to the comparators 112, respectively, derived from one or more input reference voltages (Vref). The adjusted reference voltages are variable and are controlled by the switch control module 416 based on the delayed digital outputs from the buffer module 204. As described above, the reference voltages supplied to the comparators of the example delta sigma modulators of FIGS. 1 and 3 are fixed. Relative to the example delta sigma modulator of FIG. 3, the example delta sigma modulator of FIG. 5 consumes less power.
Referring now to FIG. 6, an example schematic of the switching module 412 is presented. A positive reference potential (Vrefp) is connected at a node 504. A negative reference potential (Vrefn) is connected at a node 508. One or more resistors, such as resistors 512 and 516, are connected between the node 504 and a node 520.
A switching device 524 is connected between the node 504 and a node 528. A switching device 532 is connected between the node 520 and the node 528. A switching device 536 is connected between the node 504 and a node 540. A switching device 544 is connected between the One or more resistors, such as resistor 548, are connected between the node 520 and a node 552. One or more resistors, such as resistor 556, are connected between the node 552 and a node 560. A switching device 564 is connected between the node 560 and the node 528. A switching device 568 is connected between the node 560 and the node 540.
One or more resistors, such as resistor 572, are connected between the node 560 and a node 576. A switching device 580 is connected between the node 576 and a node 584. A switching device 588 is connected between the node 576 and a node 592. A switching device 596 is connected between the node 552 and the node 584. A switching device 600 is connected between the node 552 and the node 592.
One or more resistors, such as resistor 604, are connected between the node 576 and a node 608. A switching device 612 is connected between the node 608 and the node 528. A switching device 616 is connected between the node 608 and the node 540.
A switching device 620 is connected between the node 608 and a node 624. A switching device 628 is connected between the node 608 and a node 632.
One or more resistors, such as resistor 636, are connected between the node 608 and a node 640. A switching device 644 is connected between the node 640 and the node 584. A switching device 648 is connected between the node 640 and
One or more resistors, such as resistor 652, are connected between the node 640 and a node 656. A switching device 660 is connected between the node 656 and the node 624. A switching device 664 is connected between the node 656 and the node 632.
One or more resistors, such as resistor 668, are connected between the node 656 and a node 672. A switching device 676 is connected between the node 672 and the node 584. A switching device 680 is connected between the node 672 and the node 592.
One or more resistors, such as resistor 684, are connected between the node 672 and a node 688. A switching device 692 is connected between the node 688 and the node 624. A switching device 696 is connected between the node 688 and the node 632.
One or more resistors, such as resistors 700 and 704, are connected between the node 688 and the node 508. A switching device 708 is connected between the node 508 and the node 624. A switching device 712 is connected between the node 508 and the node 632.
The resistors of the switching module 412 provide voltage dividers. The states of the switching devices control which resistors are used to provide the voltage dividers and, therefore, the reference potentials provided to the comparators 112. The switch control module 416 controls the states of the switching devices, as discussed further below, to control the respective reference potentials provided to the comparators 112.
Referring now to FIG. 7, a functional block diagram including an example implementation of the switch control module 416. The switch control module 416 controls the states of the switching devices of the switching module 412 based on the delayed digital outputs of the comparators 112.
In the example of FIG. 7, the buffer module 204 is illustrated as two different one-half clock cycle buffer modules. One of the one-half clock period buffer modules receives the three digital bits of a positive differential output of the comparators 112 (Dop), and the other one of the one-half clock period buffer modules receives the three digital bits of a negative differential output of the comparators 112 (Don). Each of the one-half clock period buffer modules delays the output of the received digital bits for one-half of a cycle of the clock signal (Ts) input to the comparators 112.
The switch control module 416 generates signals that are applied to the switching devices of the switching module 412. The switch control module 416 may include one or more encoders, such as thermometer to binary (T2B) encoders 800 and 804. While T2B encoders are shown and described, another suitable type of encoder may be used.
The T2B encoder 800 sets the states of first and second positive digital signals (BP1 and BP0) based on the three delayed digital bits of the positive differential output of the comparators 112. The T2B encoder 804 sets the states of first and second negative digital signals (BN1 and BN0) based on the three delayed digital bits of the negative differential output of the comparators 112.
The switch control module 416 also includes one or more digital logic gates that generate switching signals that are applied to the switching devices of the switching module 412 and that control the states of the switching devices. For example, the switch control module 416 may include first, second, third, and fourth AND gates 808, 812, 816, and 820, respectively. While an example including AND gates is shown and described, another suitable arrangement of logic gates may be implemented.
The first AND gate 808 generates a first switching signal (BP1, BP0) as a logical AND function of the first positive digital signal (BP1) and the second positive digital signal (BP0). Ones of the switching devices labeled BP1BP0 in FIG. 6 may open and close based on the state of the first switching signal. For example, the ones of the switching devices labeled BP1BP0 in FIG. 6 may close when the first switching signal is in a first state (e.g., digital 1) and may open when the first switching signal is in a second state (e.g., digital 0).
The second AND gate 812 generates a second switching signal (BP1, BN0) as a logical AND function of the first positive digital signal (BP1) and the second negative digital signal (BN0). Ones of the switching devices labeled BP1BN0 in FIG. 6 may open and close based on the state of the second switching signal. For example, the ones of the switching devices labeled BP1BN0 in FIG. 6 may close when the second switching signal is in the first state and may open when the second switching signal is in the second state.
The third AND gate 816 generates a third switching signal (BP0, BN1) as a logical AND function of the second positive digital signal (BP0) and the first negative digital signal (BN1). Ones of the switching devices labeled BP0BN1 in FIG. 6 may open and close based on the state of the third switching signal. For example, the ones of the switching devices labeled BP0BN1 in FIG. 6 may close when the third switching signal is in the first state and may open when the third switching signal is in the second state.
The fourth AND gate 820 generates a fourth switching signal (BP0, BN0) as a logical AND function of the second positive digital signal (BP0) and the second negative digital signal (BN0). Ones of the switching devices labeled BP0BN0 in FIG. 6 may open and close based on the state of the fourth switching signal. For example, the ones of the switching devices labeled BP0BN0 in FIG. 6 may close when the fourth switching signal is in the first state and may open when the fourth switching signal is in the second state.
A table illustrating example possible combinations of the digital outputs of the comparators 112, example resulting outputs of the T2B encoders 800 and 804, and example resulting states of the first-fourth switching signals is provided below.




















DOP
 DON 
BP1
 BP0 
BN1
 BN0 
BP1BP0
 BP1BN0 
BP0BN1
 BN1BN0 
ΔVref







111
000
1
1
0
0
1
0
0
0
−/+VFS/4 


011
100
1
0
0
1
0
1
0
0
−/+VFS/12


001
110
0
1
1
0
0
0
1
0
+/−VFS/12


000
111
0
0
1
1
0
0
0
1
+/−VFS/4 









The table also includes example adjustments (ΔVref) to the reference potentials that may result in each case. The reference potentials (Vrefp and Vrefn) are adjusted based on the adjustment ΔVref to produce the respective reference potentials that are provided to the comparators 112. While the example of the switch control module 416 controlling four different groups of the switching devices of the switching module 412 is shown and discussed, the switch control module 416 may control the switching devices individually or using another suitable grouping.
FIG. 8 includes a schematic of an example third order continuous time sigma delta modulator having a two-bit quantizer that can be represented by the example of FIG. 5. As shown in FIG. 8, a dynamic element matching (DEM) module may be implemented.
FIG. 9 is an example graph of signal to quantization noise ratio (SQNR) versus delay of the quantizer and the DEM of the example third order continuous time sigma delta modulator of FIG. 8. FIG. 10 is an example graph including a power spectral density (PSD) of the example third order continuous time sigma delta modulator of FIG. 8.
Referring now to FIG. 11, a flowchart depicting an example method performed by a delta sigma modulator is presented. Control may begin with 904 where the comparators 112 generate the digital outputs based on comparisons of a given input and the respective references.
At 908, the buffer module 204 delays the provision of the digital outputs to the DAC 116 and to the reference module 408 for a predetermined period, such as one-half of a cycle of the clock signal input to the comparators 112. At 912, the reference module 408 generates the respective references provided to the comparators 112 based on the delayed digital outputs. Also at 912, the DAC 116 generates the analog value based on the delayed digital outputs, and the input to the comparators 112 is updated. At 916, the comparators 112 detect whether an edge (e.g., rising or falling) of the clock signal is present. If 916 is true, control returns to 904 where the comparators update the digital outputs based on comparisons of the updated input with the respective references. If 916 is false, control may remain at 916.
The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.
In this application, including the definitions below, the term ‘module’ or the term ‘controller’ may be replaced with the term ‘circuit.’ The term ‘module’ may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.
The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module.
The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, data structures, and/or objects. The term shared processor circuit encompasses a single processor circuit that executes some or all code from multiple modules. The term group processor circuit encompasses a processor circuit that, in combination with additional processor circuits, executes some or all code from one or more modules. References to multiple processor circuits encompass multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term shared memory circuit encompasses a single memory circuit that stores some or all code from multiple modules. The term group memory circuit encompasses a memory circuit that, in combination with additional memories, stores some or all code from one or more modules.
The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).
The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks and flowchart elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.
The computer programs include processor-executable instructions that are stored on at least one non-transitory, tangible computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc.
The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language) or XML (extensible markup language), (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective C, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Peri, Pascal, Curl, OCaml, Javascript®, HTML5, Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, and Python®.
None of the elements recited in the claims are intended to be a means-plus-function element within the meaning of 35 U.S.C. §112(f) unless an element is expressly recited using the phrase “means for,” or in the case of a method claim using the phrases “operation for” or “step for.”

## Claims

1. A continuous time delta sigma modulator, comprising:
a quantizer that includes:
a first comparator that generates a first digital output based on a comparison of a first reference potential with an input generated based on a sample of an analog signal; and
a second comparator that generates a second digital output based on a comparison of a second reference potential with the input generated based on the sample of the analog signal; and

a reference module that varies the first and second reference potentials based on the first and second digital outputs.

2. The continuous time delta sigma modulator of claim 1 further comprising:
a buffer module that receives the first and second digital outputs, that delays outputting the first and second digital outputs for less than one cycle of a clock signal, and that outputs the delayed first and second digital outputs to the reference module,
wherein the reference module varies the first and second reference potentials based on the delayed first and second digital outputs, and
wherein the first and second comparators update the first and second digital outputs each cycle of the clock signal.

3. The continuous time delta sigma modulator of claim 2 wherein the buffer module delays outputting the first and second digital outputs for one-half of the cycle of the clock signal.

4. The continuous time delta sigma modulator of claim 2 wherein the reference module includes:
a switching module that includes a plurality of switching devices and a plurality of resistors that regulate the first and second reference potentials; and
a switch control module that controls states of the switching devices based on the delayed first and second digital outputs.

5. The continuous time delta sigma modulator of claim 4 wherein the switch control module includes:
at least one thermometer to binary encoder that encodes the delayed first and second digital outputs to produce encoded outputs; and
at least one logic gate that performs a digital logic function based on the encoded outputs to produce at least one switching signal and that applies the at least one switching signal to one or more of the switching devices of the switching module.

6. The continuous time delta sigma modulator of claim 4 wherein the switch control module includes:
a first thermometer to binary encoder that generates first and second encoded outputs based on the delayed first and second digital outputs;
a second thermometer to binary encoder that generates third and fourth encoded outputs based on the delayed first and second digital outputs;
a first AND gate that generates a first switching signal based on a logical AND function of the first and second encoded outputs and that applies the first switching signal to a first set of one or more of the switching devices;
a second AND gate that generates a second switching signal based on a logical AND function of the first and third encoded outputs and that applies the second switching signal to a second set of one or more of the switching devices;
a third AND gate that generates a third switching signal based on a logical AND function of the second and third encoded outputs and that applies the third switching signal to a third set of one or more of the switching devices; and
a fourth AND gate that generates a fourth switching signal based on a logical AND function of the third and fourth encoded outputs and that applies the fourth switching signal to a fourth set of one or more of the switching devices.

7. The continuous time delta sigma modulator of claim 2 further comprising:
a digital to analog converter (DAC) that converts the delayed first and second digital outputs into an analog value; and
an integrator that generates the input based on the sample of the analog signal and the analog value.

8. The continuous time delta sigma modulator of claim 7 further comprising:
a subtractor that subtracts the analog value from the sample of the analog signal to produce an output,
wherein the integrator generates the input based on an integral of the output of the subtractor.

9. The continuous time delta sigma modulator of claim 1 wherein:
the quantizer further includes N additional comparators that generate N additional digital outputs based on comparisons of N additional reference potentials, respectively, with the input generated based on the sample of the analog signal;
N is an integer greater than zero; and
the reference module varies the first reference potential, the second reference potential, and the N additional reference potential based on the first digital output, the second digital output, and the N additional digital outputs.

10. The continuous time delta sigma modulator of claim 9 wherein the reference module includes:
a switching module that includes a plurality of switching devices and a plurality of resistors that regulate the first reference potential, the second reference potential, and the N additional reference potentials; and
a switch control module that controls states of the switching devices based on the first digital output, the second digital output, and the N additional digital outputs.

11. A method comprising:
using a first comparator of a quantizer of a continuous time delta sigma modulator, generating a first digital output based on a comparison of a first reference potential with an input generated based on a sample of an analog signal;
using a second comparator of the quantizer of the continuous time delta sigma modulator, generating a second digital output based on a comparison of a second reference potential with the input generated based on the sample of the analog signal; and
varying the first and second reference potentials based on the first and second digital outputs.

12. The method of claim 11 further comprising:
using a buffer module of the continuous time delta sigma modulator, receiving the first and second digital outputs, delaying outputting the first and second digital outputs for less than one cycle of a clock signal, and outputting the delayed first and second digital outputs;
varying the first and second reference potentials based on the delayed first and second digital outputs; and
using the first and second comparators, updating the first and second digital outputs each cycle of the clock signal.

13. The method of claim 12 further comprising, using the buffer module, delaying outputting the first and second digital outputs for one-half of the cycle of the clock signal.

14. The method of claim 12 further comprising:
using a switching module that includes a plurality of switching devices and a plurality of resistors, regulating the first and second reference potentials; and
controlling states of the switching devices based on the delayed first and second digital outputs.

15. The method of claim 14 further comprising:
using at least one thermometer to binary encoder, encoding the delayed first and second digital outputs to produce encoded outputs; and
using at least one logic gate, performing a digital logic function based on the encoded outputs to produce at least one switching signal and applying the at least one switching signal to one or more of the switching devices of the switching module.

16. The method of claim 14 further comprising:
using a first thermometer to binary encoder, generating first and second encoded outputs based on the delayed first and second digital outputs;
using a second thermometer to binary encoder, generating third and fourth encoded outputs based on the delayed first and second digital outputs;
using a first AND gate, generating a first switching signal based on a logical AND function of the first and second encoded outputs and that applying the first switching signal to a first set of one or more of the switching devices;
using a second AND gate, generating a second switching signal based on a logical AND function of the first and third encoded outputs and applying the second switching signal to a second set of one or more of the switching devices;
using a third AND gate, generating a third switching signal based on a logical AND function of the second and third encoded outputs and applying the third switching signal to a third set of one or more of the switching devices; and
using a fourth AND gate, generating a fourth switching signal based on a logical AND function of the third and fourth encoded outputs and applying the fourth switching signal to a fourth set of one or more of the switching devices.

17. The method of claim 12 further comprising:
using a digital to analog converter (DAC), converting the delayed first and second digital outputs into an analog value; and
using an integrator, generating the input based on the sample of the analog signal and the analog value.

18. The method of claim 17 further comprising:
using a subtractor, subtracting the analog value from the sample of the analog signal to produce an output; and
using the integrator, generating the input based on an integral of the output of the subtractor.

19. The method of claim 11 further comprising:
using N additional comparators of the quantizer of the continuous time delta sigma modulator, generating N additional digital outputs based on comparisons of N additional reference potentials, respectively, with the input generated based on the sample of the analog signal;
N is an integer greater than zero; and
varying the first reference potential, the second reference potential, and the N additional reference potential based on the first digital output, the second digital output, and the N additional digital outputs.

20. The method of claim 19 further comprising:
using a switching module that includes a plurality of switching devices and a plurality of resistors, regulating the first reference potential, the second reference potential, and the N additional reference potentials; and
controlling states of the switching devices based on the first digital output, the second digital output, and the N additional digital outputs.