WO2006039510A2 - Continuous-time digital amplifier - Google Patents

Continuous-time digital amplifier

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Publication number
WO2006039510A2
WO2006039510A2 PCT/US2005/035223 US2005035223W WO2006039510A2 WO 2006039510 A2 WO2006039510 A2 WO 2006039510A2 US 2005035223 W US2005035223 W US 2005035223W WO 2006039510 A2 WO2006039510 A2 WO 2006039510A2
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WO
WIPO (PCT)
Prior art keywords
continuous
time digital
current
voltage
signal
Prior art date
Application number
PCT/US2005/035223
Other languages
French (fr)
Other versions
WO2006039510A3 (en
WO2006039510A9 (en
Inventor
Yannis Tsividis
Original Assignee
The Trustees Of Columbia University In The City Ofnew York
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Filing date
Publication date
Application filed by The Trustees Of Columbia University In The City Ofnew York filed Critical The Trustees Of Columbia University In The City Ofnew York
Publication of WO2006039510A2 publication Critical patent/WO2006039510A2/en
Publication of WO2006039510A9 publication Critical patent/WO2006039510A9/en
Publication of WO2006039510A3 publication Critical patent/WO2006039510A3/en

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/30—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/21—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
    • H03F3/217—Class D power amplifiers; Switching amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
    • H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit

Definitions

  • This invention relates generally to continuous-time digital representation and amplification of continuous-time signals.
  • a continuous-time digital amplifier includes a bit waveform generator for producing one or more bit waveforms from a continuous-time digital signal.
  • the continuous-time digital amplifier also includes a fractional current source, controlled by the associated bit waveform, for each of the one or more bit waveforms.
  • the output currents from the fractional current sources associated with the bit waveforms are combined to form a composite current.
  • This composite current is used to drive a load.
  • the amplifier uses fractional voltage sources instead of fractional current sources, thus forming composite voltage across the load.
  • the bit waveforms are weighted by fractional powers of two.
  • the amplifier also includes a quantizer for producing the continuous-time digital signal from an analog signal.
  • the quantizer produces the continuous-time digital signal without sampling.
  • the amplifier includes a current source for supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current.
  • Embodiments may includes one or more switches controlled by a sign bit for accommodating a bipolar continuous-time digital signal. The switches control a direction of the composite current through the load.
  • the amplifier includes an envelope detector for detecting the amplitude of the analog signal and for producing a control signal, and a gain element for amplifying the analog signal according to the control signal, so as to produce an amplified analog signal.
  • the amplifier further includes a current source for supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current.
  • the envelope detector produces the control signal as a function of the analog signal, or the amplified analog signal, or both, and the current from the current source varies as a function of the control signal.
  • the continuous-time digital amplifier includes a filter for filtering the composite current before the composite current flows through the load.
  • the filter filters the composite voltage across the load.
  • the continuous-time digital signal into the amplifier can change only at one of a predetermined set of discrete time values.
  • the continuous-time digital may be disposed within a negative feedback loop, or other feedback system.
  • FIG. 1 shows one way of representing an input analog signal with a quantized and digitized continuous-time signal
  • FIG. 2 is an exemplary circuit for implementing the quantized signal of FIG. l;
  • FIG. 3 Is an exemplary continuous time digital amplifier
  • FIG. 4 is a continuous-time digital system including the digital amplifier of
  • FIG. 5 is continuous-time digital amplifier arranged in a negative feedback loop.
  • the described embodiment quantizes and digitizes an input analog signal without sampling, so as to produce a continuous-time digital signal.
  • This continuous-time digital signal is a function of continuous time, such that a set of pairs, e.g., (I 1 , x ⁇ completely describes the continuous-time digital signal (where x; represents the amplitude value, and ti represents the time at which that amplitude value was reached). Since the amplitude levels are known, a type of delta modulation signal may also be used ⁇ see, for example, "Asynchronous delta modulation system," Electronic Letters, vol. 2, pp.95-96, 1966).
  • the quantized and digitized information related to the input analog signal can be stored in a memory medium (such as magnetic tape or some other continuous-time storage medium) and may be later transmitted, and/or processed as described herein.
  • FIG. 1 shows one way of representing an input analog signal x(t) with a quantized continuous-time signal w(t).
  • the continuous-time bit waveforms that form w(t) are shown below x(t) and w(t), where bi t represents the least significant bit of the continuous- time digital signal.
  • the embodiment depicted by FIG. 1 shows only three bits in the continuous-time digital signal, it is understood that the digitized continuous-time signal w(t) may include any number of bits.
  • Other embodiments for representing an input analog signal with a quantized and digitized continuous-time signal may also be used.
  • the bit waveforms are continuous-time ones. This is to be distinguished from the standard representation using discrete-time digital signals of the classical kind, which represent samples of the original signal taken at constant intervals.
  • a "pseudo-continuous" version of what is described here may also be used. In such a version, the time instants t k shown in FIG. 1 are allowed to take any one of a set of discrete values, provided the resulting time quantization is fine enough.
  • This representation has the advantage that it may be stored in a discrete-time medium.
  • bit waveforms fa k (t) can be used to control active elements (e.g., transistors and other switching components) directly, to reproduce the analog quantized version w(t), in the form:
  • Equation 1 is a summation of terms weighted by fractional powers of two (i.e., Vz, VA, 1/8, 1/16, etc.), other mathematical forms can also be used to represent w(t).
  • Equation 1 shown schematically in FIG. 2 as system 200, is actually a digital to analog converter (DAC), which can be used to directly drive a load (a loudspeaker for example).
  • DAC digital to analog converter
  • Each current source 202a through 202c represents a fractional current (2 "n I) weighted by a coefficient (b n ) from Equation 1.
  • FIG. 3 depicts an exemplary embodiment of the system 200 described above.
  • This embodiment an implementation of a differential amplifier 300, drives a load 308 such as a loudspeaker.
  • This embodiment incorporates switches 302 controlled by a sign bit (and its complement) to facilitate bipolar signals.
  • the switches 302 may include any type of component known in the art capable of opening and closing a circuit in response to a control signal (i.e., the sign bit).
  • Equation 1 A straightforward code (i.e., the particular form of Equation 1) is assumed in the exemplary embodiments of FIGs. 2 and 3, but other codes can be used as well, as described for example in United States Patent No. 4,580,111.
  • a sign bit can be used as part of the code, so that bidirectional current sources can be used, corresponding to bipolar signals, as is done, for example, in the exemplary embodiment below.
  • FIG. 3 uses only two coefficients bt and b 2 (and their complements) from Equation 1, although in general any number of coefficients may be used.
  • the coefficients operate switches 304 as described above to control the current source transistors 306, that in turn drive the load 308.
  • a pair of switches 304 combined with a current source transistor 306 thus form a fractional current source that is controlled by a bit waveform.
  • Magnitude control of the signal driving the load 308 e.g., volume control for a loudspeaker load
  • Any residual error at the output of the digital amplifier 300 can be filtered out prior to the load 308, using a continuous-time filter, as described above and as shown in FIG. 4.
  • a complete amplifier for processing an analog signal requires a continuous- time analog to digital converter (ADC) 410 at the front end for generating continuous- time digital signal and the bit waveforms, as shown in FIG. 4.
  • ADC analog to digital converter
  • Alternative embodiments use different versions of the architecture described herein. For example, one embodiment uses cascode or other type of high-performance current sources. Another embodiment uses differential pairs as current switches. Another embodiment uses the bit waveforms to control fractional voltage sources instead of current sources. Another embodiment varies V dd to improve efficiency. Many other such modifications that incorporate components and techniques that are well known in the art may also be used to modify the underlying concepts described herein.
  • variable current source (I) allows one to also incorporate companding in the implementation of FIG. 3, as shown in FIG. 4.
  • the envelope detector e (402) controls the gain element g (404) and makes it large, so that the amplitude of x(t) is large, thus exercising most of the ADC quantization steps.
  • the gain element g (404) is greater than one in order to increase the amplitude of x(t) .
  • the gain element g (404) can be can also be less than or equal to one to provide for unity gain or attenuation through the amplifier.
  • the control signal 406 makes the "I" in the continuous time differential amplifier small (see FIG. 3), thus resulting in a small amplitude for y(t).
  • a filter 408 may be included to process the signal y(t) driving the load in order to reduce the power of the undesired components of y(t) beyond the baseband frequencies.
  • FIG. 5 shows another embodiment of the continuous-time digital amplifier described herein.
  • a continuous -time digital power amplifier 502 is arranged in a feedback loop 504 with negative feedback 506.
  • This negative feedback 506 corrects for residual nonlinearities of the power amplifier, and makes the overall system very linear, with very low distortion.
  • the continuous-time digital amplifier could use either fractional current sources or fractional voltage sources as described herein.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

A continuous-time digital amplifier (200, 300) includes a bit waveform generator (410) for producing one or more bit waveforms from a continuous-time digital signal (b). The amplifier also includes a fractional current source (202a-202c) for each of the one or more bit waveforms. Each fractional current source is controlled by the associated bit waveform. The output currents from the fractional current sources associated with the bit waveforms are combined to form a composite current that is used to drive a load. The amplifier may alternatively use fractional voltage sources instead of fractional current sources controlled by the bit waveforms, to generate a composite voltage to drive a load (308). The amplifier may also include a quantizer (410) for producing the continuous-time digital signal from an analog signal. The quantizer (410) produces the continuous-time digital signal without periodic sampling.

Description

CONTINUOUS-TIME DIGITAL AMPLIFIER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit U.S. Provisional Patent Application Serial
No. 60/614,575, filed September 30, 2004, entitled "Continuous-Time Digital Amplifier."
[0002] This application is related to U.S. Patent Application Serial No. 10/878,155, filed June 28, 2004, entitled "Continuous-Time Digital Signal Generation, Transmission, Storage and Processing," of common inventor and assignee, and which is hereby incorporated by reference in its entirety.
[0003] This application is also related to U.S. Patent Application Serial No.
60/633,747, filed December 7, 2004, entitled "Modulation Scheme With Improved Performance," of common inventor and assignee, and which is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0004] This invention relates generally to continuous-time digital representation and amplification of continuous-time signals.
BACKGROUND
[0005] Conventional digital amplifiers suffer from aliasing and produce quantization "noise" which includes numerous components non-harmonically related to the signal being processed. Techniques such as dithering and non-uniform sampling may reduce or modify one or both of these undesired effects, but residual aliasing and/or quantization noise typically remains even after applying such techniques.
SUMMARY OF THE INVENTION
[0006] Digitally processing an analog signal that has been quantized without sampling results in no aliasing and reduces in-band quantization error as compared to conventional digital processing techniques. The following description sets forth a continuous-time digital system that quantizes an analog signal without sampling and amplifies an input signal with substantially the same characteristics as a classical analog amplifier.
[0007] In one aspect, a continuous-time digital amplifier includes a bit waveform generator for producing one or more bit waveforms from a continuous-time digital signal. The continuous-time digital amplifier also includes a fractional current source, controlled by the associated bit waveform, for each of the one or more bit waveforms. The output currents from the fractional current sources associated with the bit waveforms are combined to form a composite current. This composite current is used to drive a load. In some embodiments, the amplifier uses fractional voltage sources instead of fractional current sources, thus forming composite voltage across the load. In one embodiment, the bit waveforms are weighted by fractional powers of two.
[0008] In one embodiment, the amplifier also includes a quantizer for producing the continuous-time digital signal from an analog signal. The quantizer produces the continuous-time digital signal without sampling.
[0009] In another embodiment, the amplifier includes a current source for supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current. Embodiments may includes one or more switches controlled by a sign bit for accommodating a bipolar continuous-time digital signal. The switches control a direction of the composite current through the load.
[0010] In one embodiment, the amplifier includes an envelope detector for detecting the amplitude of the analog signal and for producing a control signal, and a gain element for amplifying the analog signal according to the control signal, so as to produce an amplified analog signal. The amplifier further includes a current source for supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current. The envelope detector produces the control signal as a function of the analog signal, or the amplified analog signal, or both, and the current from the current source varies as a function of the control signal.
[0011] In some embodiments, the continuous-time digital amplifier includes a filter for filtering the composite current before the composite current flows through the load. In voltage-mode operation, the filter filters the composite voltage across the load. In some embodiments, the continuous-time digital signal into the amplifier can change only at one of a predetermined set of discrete time values. The continuous-time digital may be disposed within a negative feedback loop, or other feedback system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows one way of representing an input analog signal with a quantized and digitized continuous-time signal;
[0013] FIG. 2 is an exemplary circuit for implementing the quantized signal of FIG. l;
[0014] FIG. 3 Is an exemplary continuous time digital amplifier; and,
[0015] FIG. 4 is a continuous-time digital system including the digital amplifier of
FIG. 3.
[0016] FIG. 5 is continuous-time digital amplifier arranged in a negative feedback loop.
DETAILED DESCRIPTION
[0017] The described embodiment quantizes and digitizes an input analog signal without sampling, so as to produce a continuous-time digital signal. This continuous-time digital signal is a function of continuous time, such that a set of pairs, e.g., (I1, xθ completely describes the continuous-time digital signal (where x; represents the amplitude value, and ti represents the time at which that amplitude value was reached). Since the amplitude levels are known, a type of delta modulation signal may also be used {see, for example, "Asynchronous delta modulation system," Electronic Letters, vol. 2, pp.95-96, 1966). In some embodiments, the quantized and digitized information related to the input analog signal can be stored in a memory medium (such as magnetic tape or some other continuous-time storage medium) and may be later transmitted, and/or processed as described herein.
[0018] Note that in addition to quantizing and digitizing the amplitude information related to the input analog signal, the timing information related to when quantized and digitized amplitude information changes states can also be stored on storage media, along with the associated amplitude information. Note also that this stored information does not need to be processed as described herein; the generation, storage and/or transmission of the quantized and digitized continuous-time signal have utility in and of themselves. [0019] FIG. 1 shows one way of representing an input analog signal x(t) with a quantized continuous-time signal w(t). In this embodiment, the continuous-time bit waveforms that form w(t) are shown below x(t) and w(t), where bit represents the least significant bit of the continuous- time digital signal. Although the embodiment depicted by FIG. 1 shows only three bits in the continuous-time digital signal, it is understood that the digitized continuous-time signal w(t) may include any number of bits. Other embodiments for representing an input analog signal with a quantized and digitized continuous-time signal may also be used. It is emphasized that what is different here from the prior art is that the bit waveforms are continuous-time ones. This is to be distinguished from the standard representation using discrete-time digital signals of the classical kind, which represent samples of the original signal taken at constant intervals. However, it is understood that a "pseudo-continuous" version of what is described here may also be used. In such a version, the time instants tk shown in FIG. 1 are allowed to take any one of a set of discrete values, provided the resulting time quantization is fine enough. This representation has the advantage that it may be stored in a discrete-time medium.
[0020] The bit waveforms fak(t) can be used to control active elements (e.g., transistors and other switching components) directly, to reproduce the analog quantized version w(t), in the form:
N w(t) = Y42"" hn (t) Equation
1
[0021] Although Equation 1 is a summation of terms weighted by fractional powers of two (i.e., Vz, VA, 1/8, 1/16, etc.), other mathematical forms can also be used to represent w(t). Equation 1, shown schematically in FIG. 2 as system 200, is actually a digital to analog converter (DAC), which can be used to directly drive a load (a loudspeaker for example). Each current source 202a through 202c represents a fractional current (2"nI) weighted by a coefficient (bn) from Equation 1. The system 200 thus implements a "digital amplifier." Unlike the common use of this term in the prior art, a "digital amplifier" as used herein does not imply or require the use of pulse-width modulation. Any residual error at the output of the digital amplifier can be filtered out using a continuous-time filter. [0022] FIG. 3 depicts an exemplary embodiment of the system 200 described above. This embodiment, an implementation of a differential amplifier 300, drives a load 308 such as a loudspeaker. This embodiment incorporates switches 302 controlled by a sign bit (and its complement) to facilitate bipolar signals. The switches 302 may include any type of component known in the art capable of opening and closing a circuit in response to a control signal (i.e., the sign bit). The control signal shown next to each switch is assumed to close the switch if its value is "1," and to open it if its values is "0," although other conventions may also be used. A straightforward code (i.e., the particular form of Equation 1) is assumed in the exemplary embodiments of FIGs. 2 and 3, but other codes can be used as well, as described for example in United States Patent No. 4,580,111. In addition, a sign bit can be used as part of the code, so that bidirectional current sources can be used, corresponding to bipolar signals, as is done, for example, in the exemplary embodiment below. The example of FIG. 3 uses only two coefficients bt and b2 (and their complements) from Equation 1, although in general any number of coefficients may be used. The coefficients operate switches 304 as described above to control the current source transistors 306, that in turn drive the load 308. A pair of switches 304 combined with a current source transistor 306 thus form a fractional current source that is controlled by a bit waveform. Magnitude control of the signal driving the load 308 (e.g., volume control for a loudspeaker load) can be achieved by varying the magnitude of the current source (I) 310. Any residual error at the output of the digital amplifier 300 can be filtered out prior to the load 308, using a continuous-time filter, as described above and as shown in FIG. 4.
[0023] A complete amplifier for processing an analog signal requires a continuous- time analog to digital converter (ADC) 410 at the front end for generating continuous- time digital signal and the bit waveforms, as shown in FIG. 4. However, if the signal to be processed is already in continuous-time digital form, the ADC is not required. Alternative embodiments use different versions of the architecture described herein. For example, one embodiment uses cascode or other type of high-performance current sources. Another embodiment uses differential pairs as current switches. Another embodiment uses the bit waveforms to control fractional voltage sources instead of current sources. Another embodiment varies Vdd to improve efficiency. Many other such modifications that incorporate components and techniques that are well known in the art may also be used to modify the underlying concepts described herein. [0024] The use of a variable current source (I) allows one to also incorporate companding in the implementation of FIG. 3, as shown in FIG. 4. If x(t) has a small amplitude, the envelope detector e (402) controls the gain element g (404) and makes it large, so that the amplitude of x(t) is large, thus exercising most of the ADC quantization steps. In this particular embodiment, the gain element g (404) is greater than one in order to increase the amplitude of x(t) . In general, however, the gain element g (404) can be can also be less than or equal to one to provide for unity gain or attenuation through the amplifier. At the same time, the control signal 406 makes the "I" in the continuous time differential amplifier small (see FIG. 3), thus resulting in a small amplitude for y(t).
[0025] A filter 408 may be included to process the signal y(t) driving the load in order to reduce the power of the undesired components of y(t) beyond the baseband frequencies.
[0026] FIG. 5 shows another embodiment of the continuous-time digital amplifier described herein. In this embodiment, a continuous -time digital power amplifier 502 is arranged in a feedback loop 504 with negative feedback 506. This negative feedback 506 corrects for residual nonlinearities of the power amplifier, and makes the overall system very linear, with very low distortion. In this embodiment, the continuous-time digital amplifier could use either fractional current sources or fractional voltage sources as described herein.
[0027] Other aspects, modifications, and embodiments are within the scope of the following claims.

Claims

What is claimed is:
1. A continuous-time digital amplifier, comprising: a bit waveform generator for producing one or more bit waveforms from a continuous-time digital signal; for each of the one or more bit waveforms, a fractional current source controlled by the associated bit waveform; wherein the output currents from the fractional current sources associated with the bit waveforms are combined to form a composite current that is used to drive a load.
2. The continuous-time digital amplifier of claim 1, further including a quantizer for producing the continuous-time digital signal from an analog signal, wherein the quantizer produces the continuous-time digital signal without sampling.
3. The continuous-time digital amplifier of claim 1, further including a current source for supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current.
4. The continuous-time digital amplifier of claim 1, further including one or more switches controlled by a sign bit for accommodating a bipolar continuous-time digital signal.
5. The continuous-time digital amplifier of claim 4, wherein the one or more switches control a direction of the composite current through the load.
6. The continuous-time digital amplifier of claim 1, wherein the bit waveforms are weighted by fractional powers of two.
7. The continuous-time digital amplifier of claim 2, further including:
(i) an envelope detector for detecting an amplitude of the analog signal and for producing a control signal; (ii) a gain element for amplifying the analog signal according to the control signal, so as to produce an amplified analog signal; and,
(iii) a current source for supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current; wherein the envelope detector produces the control signal as a function of the analog signal, or the amplified analog signal, or both, and wherein the current from the current source varies as a function of the control signal.
8. The continuous-time digital amplifier of claim 1, further including a filter for filtering the composite current before the composite current flows through the load.
9. The continuous-time digital amplifier of claim 1, wherein the continuous- time digital signal can change only at one of a predetermined set of discrete time values.
10. The continuous-time digital amplifier of claim 1, wherein the continuous - time digital amplifier is disposed within a negative feedback loop.
11. A continuous-time digital amplifier, comprising: a bit waveform generator for producing one or more bit waveforms from a continuous-time digital signal; for each of the one or more bit waveforms, a fractional voltage source controlled by the associated bit waveform; wherein the output voltages from the fractional voltage sources associated with the bit waveforms are combined to form a composite voltage that is used to drive a load.
12. The continuous-time digital amplifier of claim 11, further including a quantizer for producing the continuous-time digital signal from an analog signal, wherein the quantizer produces the continuous-time digital signal without sampling.
13. The continuous-time digital amplifier of claim 11, further including a voltage source for supplying a voltage to the fractional voltage sources associated with the bit waveforms, wherein the voltage source is variable to control a magnitude of the composite voltage.
14. The continuous-time digital amplifier of claim 11, further including one or more switches controlled by a sign bit for accommodating a bipolar continuous-time digital signal.
15. The continuous-time digital amplifier of claim 14, wherein the one or more switches control a polarity of the composite voltage across the load.
16. The continuous-time digital amplifier of claim 11, wherein the bit waveforms are weighted by fractional powers of two.
17. The continuous-time digital amplifier of claim 12, further including:
(i) an envelope detector for detecting an amplitude of the analog signal and for producing a control signal;
(ii) a gain element for amplifying the analog signal according to the control signal, so as to produce an amplified analog signal; and,
(iii) a voltage source for supplying voltage to the fractional voltage sources associated with the bit waveforms, wherein the voltage source is variable to control a magnitude of the composite voltage; wherein the envelope detector produces the control signal as a function of the analog signal, or the amplified analog signal, or both, and wherein the voltage from the voltage source varies as a function of the control signal.
18. The continuous-time digital amplifier of claim 11, further including a filter for filtering the composite voltage before the composite current is applied across the load.
19. The continuous-time digital amplifier of claim 11, wherein the continuous- time digital signal can change only at one of a predetermined set of discrete time values.
20. The continuous-time digital amplifier of claim 11 , wherein the continuous- time digital amplifier is disposed within a negative feedback loop.
21. A method of amplifying a continuous-time digital signal, comprising: producing one or more bit waveforms from a continuous-time digital signal; for each of the one or more bit waveforms, generating a fractional current controlled by the associated bit waveform; combining the output currents from the fractional current sources associated with the bit waveforms to form a composite current, and using the composite current to drive a load.
22. The method of claim 21, further including producing the continuous-time digital signal from an analog signal, without sampling.
23. The method of claim 21, further including supplying current to the fractional current sources associated with the bit waveforms, wherein the current is variable to control a magnitude of the composite current.
24. The method of claim 21 , further including:
(i) detecting an amplitude of the analog signal and for producing a control signal;
(ii) amplifying the analog signal according to the control signal, so as to produce an amplified analog signal; and,
(iii) supplying current to the fractional current sources associated with the bit waveforms, wherein the current source is variable to control a magnitude of the composite current; wherein the control signal is a function of the analog signal, or the amplified analog signal, or both, and wherein the current varies as a function of the control signal.
25. The method of claim 21, further including filtering the composite current before the composite current flows through the load.
26. A method of amplifying a continuous-time digital signal, comprising: producing one or more bit waveforms from a continuous-time digital signal; for each of the one or more bit waveforms, generating a fractional voltage controlled by the associated bit waveform; combining the output voltages from the fractional voltage sources associated with the bit waveforms to form a composite voltage, and using the composite voltage to drive a load.
27. The method of claim 26, further including producing the continuous-time digital signal from an analog signal, without sampling.
28. The method of claim 26, further including supplying voltage to the fractional voltage sources associated with the bit waveforms, wherein the voltage is variable to control a magnitude of the composite voltage.
29. The method of claim 26, further including:
(i) detecting an amplitude of the analog signal and for producing a control signal;
(ii) amplifying the analog signal according to the control signal, so as to produce an amplified analog signal; and,
(iii) supplying voltage to the fractional current sources associated with the bit waveforms, wherein the voltage source is variable to control a magnitude of the composite voltage; wherein the control signal is a function of the analog signal, or the amplified analog signal, or both, and wherein the voltage varies as a function of the control signal.
30. The method of claim 26, further including filtering the composite voltage before the composite current flows through the load.
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GB2563093B (en) * 2017-06-02 2021-08-25 Cirrus Logic Int Semiconductor Ltd Analogue signal paths

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