# Patent

## Title
Pipelined analog-to-digital converters

## Abstract

An analog-to-digital converter including a first stage and a second stage. The first stage receives a first reference voltage and a first analog input voltage, generates a first digital signal by quantizing the first analog input voltage, and generates a first analog output voltage based on the first digital signal and the first analog input voltage. The second stage receives a second reference voltage and the first analog output voltage, in which the second reference voltage is lower than the first reference voltage. The second stage further generates a second digital signal by quantizing the first analog output voltage, and generates a second analog output voltage based on the second digital signal and the first analog output voltage.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 11/333,935 (now U.S. Pat. No. 7,541,962), filed Jan. 18, 2006. The disclosure of the above application is incorporated herein by reference.


FIELD
The present disclosure relates to pipelined analog-to-digital converters (ADCs).
BACKGROUND
Reducing power consumption of electronic devices has become increasingly important, particularly for battery powered devices such as laptop computers, personal digital assistants, cellular phones, MP3 players and other devices. Analog-to-digital converters (ADCs) are commonly used in these electronic devices to transform analog signals to digital signals. The ADC may include a pipelined ADC that utilizes multiple stages. Each stage employs a sample and hold circuit that samples an analog input voltage Vin to the pipelined ADC or a residue voltage Vres from a prior stage. In addition, each of the stages receives a reference voltage Vref.
Referring now to FIG. 1, a typical pipelined ADC 10 is shown. The ADC 10 includes a plurality of stages 12-1, 12-2, and 12-3 (collectively stages 12) that are cascaded in series. Although three stages 12-1, 12-2, and 12-3 are shown, the pipelined ADC 10 may include additional or fewer stages. Some of the A/D converter stages 12 include a sample and hold module 14 that samples and holds the analog input signal Vin or the residue signal Vres from a prior stage. A low resolution A/D subconverter module 16 quantizes the held analog signal to a resolution of Bi bits where i corresponds to the current stage of the pipelined A/D converter 10. The number of bits per stage Bi and/or the number of stages may be determined in part by the desired sampling rate and resolution. The output of the A/D subconverter module 16 is supplied to a low-resolution D/A subconverter module 18 that converts the resulting digital output signal back into an analog representation.
The D/A subconverter module 18 may have a resolution that is equivalent to that of the corresponding A/D subconverter module 16 of the same stage. A difference module 20 subtracts the analog output from the D/A subconverter module 18 from the voltage input Vin to generate a residue signal Vres. The residue signal Vres is equal to the difference between the held analog signal (Vin or Vres from the prior stage) and the reconstructed analog signal.
An analog interstage difference module 22 may be used to amplify the residue signal. The amplified residue signal is output to the next stage 12-2 of the pipelined ADC 10. The first ADC stage 12-1 of the pipelined ADC 10 operates on a most current analog input sample while the second ADC stage 12-2 operates on the amplified residue of the prior input sample. The third stage 12-3 operates on the amplified residue output by the second ADC stage 12-2.
The concurrency of operations allows a conversion speed that is determined by the time it takes in one stage. Once a current stage has completed operating on the analog input sample received from the prior stage, the current stage is available to operate on the next sample.
SUMMARY
In general, in one aspect, this specification describes an analog-to-digital converter. The analog-to-digital converter includes a first stage and a second stage. The first stage receives a first reference voltage and a first analog input voltage, generates a first digital signal by quantizing the first analog input voltage, and generates a first analog output voltage based on the first digital signal and the first analog input voltage. The second stage receives a second reference voltage and the first analog output voltage, in which the second reference voltage is lower than the first reference voltage. The second stage further generates a second digital signal by quantizing the first analog output voltage, and generates a second analog output voltage based on the second digital signal and the first analog output voltage.
In general, in another aspect, this specification describes a method for converting an analog signal to a digital signal. The method includes receiving a first analog input voltage, using a first reference voltage to generate a first digital signal by quantizing the first analog input voltage, generating a first analog output voltage based on the first digital signal and the first analog input voltage, and using a second reference voltage to generate a second digital signal by quantizing the first analog output voltage. The second reference voltage is lower than the first reference voltage.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, 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.
FIG. 1 is a functional block diagram of a pipelined analog to digital converter (ADC) according to the prior art.
FIG. 2 is a functional block diagram of an exemplary pipelined ADC according to the present invention.
FIG. 3 is a functional block diagram of another exemplary pipelined ADC according to the present invention.
FIG. 4 is a functional block diagram of an integrated circuit including a pipelined ADC according to the present invention.
FIG. 5 is a functional block diagram of an integrated circuit including an analog voltage supply, a digital voltage supply, and a pipelined ADC according to the present invention.
FIG. 6A is a functional block diagram of a hard disk drive.
FIG. 6B is a functional block diagram of a digital versatile disk (DVD).
FIG. 6C is a functional block diagram of a high definition television.
FIG. 6D is a functional block diagram of a vehicle control system.
FIG. 6E is a functional block diagram of a cellular phone.
FIG. 6F is a functional block diagram of a set top box.
FIG. 6G is a functional block diagram of a media player.



DETAILED DESCRIPTION
The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module, circuit and/or device refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 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. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.
Referring now to FIG. 2, a pipelined ADC 100 according to the present invention including multiple reference voltages Vref—i is shown, where i corresponds to the current stage of the pipelined ADC 100. The pipelined ADC 100 includes stages 112-1, 112-2, and 112-3 (collectively stages 112). Stage 112-1 includes a sample and hold module 114, an ADC module 116, a digital to analog converter (DAC) module 118, a difference module 120 and an amplifier module 122. While three stages are shown, additional or fewer stages can be used. In FIG. 2, Vref—1≧Vref—2 and Vref—1>Vref—3. The quantization of bits by a subsequent stage of the pipelined ADC 100 does not require the same signal to noise levels (SNR) as the current stage and therefore a lower reference voltage can be used for at least one of the second and third stages.
The power consumed by stages 112-1, 112-2, and 112-3 of the pipelined ADC 100 is related to the reference voltage of each stage. As a result, the pipelined ADC 100 tends to consume less power than a pipelined ADC having stages supplied with the same reference voltage as shown in FIG. 1.
Referring now to FIG. 3, a pipelined ADC 120 including different reference voltages, Vref—i is shown, where i corresponds to the current stage of the pipelined A/D converter 120. At least one of the reference voltages Vref—i is derived from an analog supply voltage Vanalog—ref for analog circuits in the system containing the ADC 120 and at least one of the reference voltages is derived from a digital supply voltage Vdigital—ref for digital circuit in the system containing the ADC 120.
Referring now to FIG. 4, an integrated circuit (IC) 200 is shown. One or more power supply 202 supplies unregulated voltage to voltage regulators 204, 206. A first voltage regulator 204 provides analog supply voltages, Vanalog—ref—1, Vanalog—ref—2, . . . and Vanalog—ref—X, where X is an integer greater than zero. A second voltage regulator 206 provides digital supply voltages, Vdigital—ref—1, Vdigital—ref—2, . . . , and Vdigital—ref—Y, where Y is an integer greater than zero. The IC 200 may also include IC components 210 to perform additional circuit functions. The first voltage regulator 204 also supplies one or more analog circuits 216 in the IC 200. The second voltage regulator 206 also supplies one or more digital circuits 214.
Referring now to FIG. 5, an integrated circuit (IC) 220 is shown. An analog voltage supply 224 generates analog supply voltages, Vanalog—ref—1, Vanalog—ref—2, . . . , and Vanalog—ref—X, where X is an integer greater than zero. A digital voltage supply 226 generates digital supply voltages, Vdigital—ref—1, Vdigital—ref—2, . . . , and Vdigital—ref—Y, where Y is an integer greater than zero. The IC 220 may also include IC components 210 to perform additional circuit functions. The analog voltage supply 224 also supplies one or more analog circuits 216 in the IC 200. The digital voltage supply 226 also supplies one or more digital circuits 214.
Referring now to FIGS. 6A-6G, various exemplary implementations of the device are shown. Referring now to FIG. 6A, the device can be implemented in one of more ADCs in a hard disk drive 400. The device may implement and/or be implemented in either or both signal processing and/or control circuits, which are generally identified in FIG. 6A at 402 and/or in a power supply 403. In some implementations, the signal processing and/or control circuit 402 and/or other circuits (not shown) in the HDD 400 may process data, perform coding and/or encryption, perform calculations, and/or format data that is output to and/or received from a magnetic storage medium 406.
The HDD 400 may communicate with a host device (not shown) such as a computer, mobile computing devices such as personal digital assistants, cellular phones, media or MP3 players and the like, and/or other devices via one or more wired or wireless communication links 408. The HDD 400 may be connected to memory 409 such as random access memory (RAM), low latency nonvolatile memory such as flash memory, read only memory (ROM) and/or other suitable electronic data storage.
Referring now to FIG. 6B, the device can be implemented in one of more ADCs in a digital versatile disc (DVD) drive 410. The device may implement and/or be implemented in either or both signal processing and/or control circuits, which are generally identified in FIG. 6B at 412, mass data storage of the DVD drive 410 and/or a power supply 413. The signal processing and/or control circuit 412 and/or other circuits (not shown) in the DVD 410 may process data, perform coding and/or encryption, perform calculations, and/or format data that is read from and/or data written to an optical storage medium 416. In some implementations, the signal processing and/or control circuit 412 and/or other circuits (not shown) in the DVD 410 can also perform other functions such as encoding and/or decoding and/or any other signal processing functions associated with a DVD drive.
The DVD drive 410 may communicate with an output device (not shown) such as a computer, television or other device via one or more wired or wireless communication links 417. The DVD 410 may communicate with mass data storage 418 that stores data in a nonvolatile manner. The mass data storage 418 may include a hard disk drive (HDD). The HDD may have the configuration shown in FIG. 6A. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The DVD 410 may be connected to memory 419 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage.
Referring now to FIG. 6C, the device can be implemented in one of more ADCs in a high definition television (HDTV) 420. The device may implement and/or be implemented in either or both signal processing and/or control circuits, which are generally identified in FIG. 6E at 422, a WLAN interface, mass data storage of the HDTV 420 and/or a power supply 423. The HDTV 420 receives HDTV input signals in either a wired or wireless format and generates HDTV output signals for a display 426. In some implementations, signal processing circuit and/or control circuit 422 and/or other circuits (not shown) of the HDTV 420 may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other type of HDTV processing that may be required.
The HDTV 420 may communicate with mass data storage 427 that stores data in a nonvolatile manner such as optical and/or magnetic storage devices. At least one HDD may have the configuration shown in FIG. 6A and/or at least one DVD may have the configuration shown in FIG. 6B. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The HDTV 420 may be connected to memory 428 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The HDTV 420 also may support connections with a WLAN via a WLAN network interface 429.
Referring now to FIG. 6D, the device may implement and/or be implemented in one of more ADCs in a control system of a vehicle 430, a WLAN interface, mass data storage of the vehicle control system and/or a power supply 433. In some implementations, the device implement a powertrain control system 432 that receives inputs from one or more sensors such as temperature sensors, pressure sensors, rotational sensors, airflow sensors and/or any other suitable sensors and/or that generates one or more output control signals such as engine operating parameters, transmission operating parameters, and/or other control signals.
The device may also be implemented in other control systems 440 of the vehicle 430. The control system 440 may likewise receive signals from input sensors 442 and/or output control signals to one or more output devices 444. In some implementations, the control system 440 may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated.
The powertrain control system 432 may communicate with mass data storage 446 that stores data in a nonvolatile manner. The mass data storage 446 may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in FIG. 6A and/or at least one DVD may have the configuration shown in FIG. 6B. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The powertrain control system 432 may be connected to memory 447 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The powertrain control system 432 also may support connections with a WLAN via a WLAN network interface 448. The control system 440 may also include mass data storage, memory and/or a WLAN interface (all not shown).
Referring now to FIG. 6E, the device can be implemented in one of more ADCs in a cellular phone 450 that may include a cellular antenna 451. The device may implement and/or be implemented in either or both signal processing and/or control circuits, which are generally identified in FIG. 6E at 452, a WLAN interface, mass data storage of the cellular phone 450 and/or a power supply 453. In some implementations, the cellular phone 450 includes a microphone 456, an audio output 458 such as a speaker and/or audio output jack, a display 460 and/or an input device 462 such as a keypad, pointing device, voice actuation and/or other input device. The signal processing and/or control circuits 452 and/or other circuits (not shown) in the cellular phone 450 may process data, perform coding and/or encryption, perform calculations, format data and/or perform other cellular phone functions.
The cellular phone 450 may communicate with mass data storage 464 that stores data in a nonvolatile manner such as optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in FIG. 6A and/or at least one DVD may have the configuration shown in FIG. 6B. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The cellular phone 450 may be connected to memory 466 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The cellular phone 450 also may support connections with a WLAN via a WLAN network interface 468.
Referring now to FIG. 6F, the device can be implemented in one of more ADCs in a set top box 480. The device may implement and/or be implemented in either or both signal processing and/or control circuits, which are generally identified in FIG. 6F at 484, a WLAN interface, mass data storage of the set top box 480 and/or a power supply 483. The set top box 480 receives signals from a source such as a broadband source and outputs standard and/or high definition audio/video signals suitable for a display 488 such as a television and/or monitor and/or other video and/or audio output devices. The signal processing and/or control circuits 484 and/or other circuits (not shown) of the set top box 480 may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other set top box function.
The set top box 480 may communicate with mass data storage 490 that stores data in a nonvolatile manner. The mass data storage 490 may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in FIG. 6A and/or at least one DVD may have the configuration shown in FIG. 6B. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The set top box 480 may be connected to memory 494 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The set top box 480 also may support connections with a WLAN via a WLAN network interface 496.
Referring now to FIG. 6G, the device can be implemented in one of more ADCs in a media player 500. The device may implement and/or be implemented in either or both signal processing and/or control circuits, which are generally identified in FIG. 6G at 504, a WLAN interface, mass data storage of the media player 500 and/or a power supply 503. In some implementations, the media player 500 includes a display 507 and/or a user input 508 such as a keypad, touchpad and the like. In some implementations, the media player 500 may employ a graphical user interface (GUI) that typically employs menus, drop down menus, icons and/or a point-and-click interface via the display 507 and/or user input 508. The media player 500 further includes an audio output 509 such as a speaker and/or audio output jack. The signal processing and/or control circuits 504 and/or other circuits (not shown) of the media player 500 may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other media player function.
The media player 500 may communicate with mass data storage 510 that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. The mass data storage may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in FIG. 6A and/or at least one DVD may have the configuration shown in FIG. 6B. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The media player 500 may be connected to memory 514 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The media player 500 also may support connections with a WLAN via a WLAN network interface 516. Still other implementations in addition to those described above are contemplated.
Those skilled in the art can now appreciate from the foregoing description that 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 to the skilled practitioner upon a study of the drawings, the specification and the following claims.

## Claims

1. An analog-to-digital converter comprising:
a first stage configured to
receive a first reference voltage and a first analog input voltage,
generate a first digital signal by quantizing the first analog input voltage, and
generate a first analog output voltage based on the first digital signal and the first analog input voltage; and

a second stage configured to
receive a second reference voltage and the first analog output voltage, wherein the second reference voltage is less than the first reference voltage,
generate a second digital signal by quantizing the first analog output voltage, and
generate a second analog output voltage based on the second digital signal and the first analog output voltage,

wherein the first reference voltage is derived from an analog supply voltage, and
wherein the second reference voltage is derived from a digital supply voltage.

2. The analog-to-digital converter of claim 1, wherein:
the first stage comprises a first sample and hold circuit configured to sample and hold the first analog input voltage to generate a held analog input voltage; and
the second stage comprises a second sample and hold circuit configured to sample and hold the first analog output voltage to generate a held analog output voltage.

3. The analog-to-digital converter of claim 2, wherein:
the first analog output voltage is equal to a difference between the held analog input voltage and a first reconstructed analog signal, the first reconstructed analog signal being an analog representation of the first digital signal; and
the second analog output voltage is equal to a difference between the held analog output voltage and a second reconstructed analog signal, the second reconstructed analog signal being an analog representation of the second digital signal.

4. An integrated circuit comprising:
the analog-to-digital converter of claim 1;
a first voltage regulator configured to provide the analog supply voltage to the analog-to-digital converter; and
a second voltage regulator configured to provide the digital supply voltage to the analog-to-digital converter.

5. A device comprising the analog-to-digital converter of claim 1.

6. The device of claim 5, wherein the device comprises a battery powered device.

7. The device of claim 6, wherein the battery powered device comprises a laptop computer, a personal digital assistant, a cellular phone, or a digital audio player.

8. The device of claim 5, comprising a hard disk drive, a digital versatile disc drive, a high definition television, a vehicle, a set top box, or a media player.

9. A method for converting an analog signal to a digital signal, the method comprising:
receiving a first analog input voltage;
using a first reference voltage to generate a first digital signal by quantizing the first analog input voltage;
generating a first analog output voltage based on the first digital signal and the first analog input voltage;
generating a second reference voltage via a digital voltage supply; and
using the second reference voltage to generate a second digital signal by quantizing the first analog output voltage, wherein the second reference voltage is less than the first reference voltage.

10. The method of claim 9, further comprising generating a second analog output voltage based on the second digital signal and the first analog output voltage.

11. The method of claim 10, further comprising:
sampling and holding the first analog input voltage to generate a held analog input voltage; and
sampling and holding the first analog output voltage to generate a held analog output voltage.

12. The method of claim 11, wherein:
the first analog output voltage is equal to a difference between the held analog input voltage and a first reconstructed analog signal, the first reconstructed analog signal being an analog representation of the first digital signal; and
the second analog output voltage is equal to a difference between the held analog output voltage and a second reconstructed analog signal, the second reconstructed analog signal being an analog representation of the second digital signal.

13. A method for converting an analog signal to a digital signal, the method comprising:
receiving a first analog input voltage;
using a first reference voltage to generate a first digital signal by quantizing the first analog input voltage;
generating a first analog output voltage based on the first digital signal and the first analog input voltage;
using a second reference voltage to generate a second digital signal by quantizing the first analog output voltage;
generating a second analog output voltage based on the second digital signal and the first analog output voltage; and
using a third reference voltage to generate a third digital signal by quantizing the second analog output voltage, wherein the third reference voltage is less than the second reference voltage,
wherein the third reference voltage is a digital reference.