Digital audio amplifier having a high power output level and low distortion

Claim 2

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producting an audio frequency analog signal to be amplified, voltage controlled attenuation means, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses, and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator having a first and second input terminal for producing a pulse train, width modulated in accordance with the amplitude of said analog singal, means for coupling a serrated waveform pulse generator to the first input terminal of said comparator and having a given sampling frequency, together with means for coupling said audio signal to the second input terminal of said comparator, and wherein said comparator includes a first non-saturating differential amplifier, and a second non-saturating differential amplifier having input terminals thereof coupled to the output terminals of said first differential amplifier.

Claim 3

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing an audio frequency analog signal to be amplified, voltage controlled attenuation means, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses, and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator having a first and second input terminal for producing a pulse train, width modulated in accordance with the amplitude of said analog signal, means for coupling a serrated waveform pulse generator to the first input terminal of said comparator and having a given sampling frequency, together with means for coupling said audio signal to the second input terminal of said comparator, further including missing pulse detection means having an input circuit for detecting a state of missing pulses within the pulse train produced by said comparator means indicative of clipping of the audio signal being amplified, and for producing an output signal indicative of missing pulse occurrences; and means for coupling said output signal of said missing pluse detection means to said voltage controlled attenuator means for attenuating said audio signal passing therethrough to prevent said clipping.

Claim 4

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing an audio frequency analog signal to be amplified, voltage controlled attenuation means, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses, and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator having a first and second input terminal for producing a pulse train, width modulated in accordance with the amplitude of said analog signal, means for coupling a serrated waveform pulse generator to the first input terminal of said comparator and having a given sampling frequency, together with means for coupling said audio signal to the second input terminal of said comparator, further including missing pulse detection means having an input circuit for detecting a state of missing pulses within the pulse train produced by said comparator means indicative of clipping of the audio signal being amplified, and for producing an output signal indicative of missing pulse occurrences; and means for coupling said output signal of said missing pluse detection means to said voltage controlled attenuator means for attenuating said audio signal passing therethrough to prevent said clipping.

Claim 5

The combination as set forth in claim 2 wherein said missing pulse detection means further includes a timing circuit for establishing a reference time interval indicative of said state of missing pulses and for producing said output signal only upon the absence of pulses, normally applied to said input circuit of said missing pulse detection means, during a time duration greater than said reference time interval.

Claim 6

The combination as set forth in claim 3 further including switching means for reinitiating timing by said timing circuit upon the application of a pulse applied to the input circuit of said missing pulse detection means.

Claim 7

The combination as set forth in claim 3 wherein said missing pulse detection means includes integrating means for producing an increasing signal with time and which functions to produce said output signal upon said increasing signal exceeding a given level and switching means for inhibiting the buildup of said increasing signal upon the detection of a pulse applied to the input circuit of said missing pulse detection means.

Claim 8

The combination as set forth in claim 5 wherein said timing circuit comprises a resistor and reactor having a given time constant proportional to said reference time interval indicative of said state of missing pulses.

Claim 9

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing an audio frequency analog signal to be amplified, voltage controlled attenuation means, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses, and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator having a first and second input terminal for producing a pulse train, width modulated in accordance with the amplitude of said analog signal, means for coupling a serrated waveform pulse generator to the first input terminal of said comparator and having a given sampling frequency, together with means for coupling said audio signal to the second input terminal of said comparator, further including a protection circuit for very rapidly disabling said modulator, including a sensing means for sensing excessive audio current being amplified, together with inhibit switching means coupled to said sensing means for generating a fixed interval inhibit signal upon the sensing of excessive audio current by said sensing means, and means for coupling said inhibit signal to said modulator for inhibiting the operation thereof.

Claim 10

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing an audio frequency analog signal to be amplified, voltage controlled attenuation means, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses, and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator having a first and second input terminal for producing a pulse train, width modulated in accordance with the amplitude of said analog signal, means for coupling a serrated waveform pulse generator to the first input terminal of said comparator and having a given sampling frequency, together with means for coupling said audio signal to the second input terminal of said comparator, further including a protection circuit for very rapidly disabling said modulator, including a sensing means for sensing excessive audio current being amplified, together with inhibit switching means coupled to said sensing means for generating a fixed interval inhibit signal upon the sensing of excessive audio current by said sensing means, and means for coupling said inhibit signal to said modulator for inhibiting the operation thereof.

Claim 11

The combination as set forth in claims 2, 3 or 4 wherein the serrated waveform has an isosceles triangular configuration and peak-to-peak voltage levels which exceed the amplitude of said audio signal until the occurrence of over modulation to produce said state of missing pulses.

Claim 12

In a digital energy conversion audio amplifier having an audio signal source for producing an audio waveform to be amplified, a feedback network, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses: reconstruction filter means for recovering the audio waveform from said width modulated trains of pulses, said reconstruction filter means having low-pass filter means for recovering said audio signal amplified by said power amplifier means and notch filter means for eliminating at least the fundamental frequency component of the switching frequency of said power amplifier means.

Claim 13

In a digital energy conversion audio amplifier having an audio signal source for producing an audio waveform to be amplified, a feedback network, a modulator for converting said analog signals to pulse width modulated trains of pulses, power amplifier means for amplifying said pulse width modulated trains of pulses: reconstruction filter means for recovering the audio waveform from said width modulated trains of pulses, said reconstruction filter means having low-pass filter means for recovering said audio signal amplified by said power amplifier means and notch filter means for eliminating at least the fundamental frequency component of the switching frequency of said power amplifier means.

Claim 14

The combination as set forth in claim 9 further including variable reactor means for tuning at least one section of said notch filter means, and means for coupling said variable reactor to said feedback network to enable reduction of output distortion by observing the output signal from said audio amplifier while actuating said variable reactor means.

Claim 15

The combination as set forth in claim 10 further including damping means coupled to said variable reactor means for damping the Q of said section of said notch filter to facilitate the observation and correction of said output signal.

Claim 16

In a digital energy conversion audio amplifier having an audio signal source for producing analog signals to be amplified, voltage controlled attenuation means, a feedback network, a modulator for converting said analog signals to a pulse width modulated train of pulses, power amplifier means for amplifying said pulse width modulated train of pulses, and reconstruction filter means, said power amplifier means including a push-pull power amplifier having a negative power supply bus and a positive power supply bus and first and second amplifier devices coupled in series across said positive and negative power supply bus, first reactance means coupled between said first and second amplifier devices and having a center tap, and push-pull amplifier crossover distortion compensation means comprising: second inductive reactance means, coupled between said center tap of first said reactance means and said reconstruction filter, and having a first and second output terminal and a tap; first coupling means for coupling said tap of said second reactance means to said center tap of said first reactance means; second coupling means for coupling said first terminal of said second inductive reactance means to said reconstruction filter; third coupling means for coupling said second terminal of said second inductive reactance means to one of said power supply busses via a first diode; fourth coupling means for coupling said second terminal of said second inductive reactance means to the other power supply bus via a second diode, said first and second diodes being back biased with respect to the polarity of the voltages upon said busses.

Claim 17

In a digital energy conversion audio amplifier having an audio signal source for producing analog signals to be amplified, voltage controlled attenuation means, a feedback network, a modulator for converting said analog signals to a pulse width modulated train of pulses, power amplifier means for amplifying said pulse width modulated train of pulses, and reconstruction filter means, said power amplifier means including a push-pull power amplifier having a negative power supply bus and a positive power supply bus and first and second amplifier devices coupled in series across said positive and negative power supply bus, first reactance means coupled between said first and second amplifier devices and having a center tap, and push-pull amplifier crossover distortion compensation means comprising: second inductive reactance means, coupled between said center tap of first said reactance means and said reconstruction filter, and having a first and second output terminal and a tap; first coupling means for coupling said tap of said second reactance means to said center tap of said first reactance means; second coupling means for coupling said first terminal of said second inductive reactance means to said reconstruction filter; third coupling means for coupling said second terminal of said second inductive reactance means to one of said power supply busses via a first diode; fourth coupling means for coupling said second terminal of said second inductive reactance means to the other power supply bus via a second diode, said first and second diodes being back biased with respect to the polarity of the voltages upon said busses.

Claim 18

The combination as set forth in claim 12 further including a third back biased diode coupled across said first reactance means and one of said amplifying devices together with a fourth back biased diode coupled across said first reactance means and the other of said amplifying devices.

Claim 19

The combination as set forth in claim 13 wherein said first reactance means comprises first and second inductors coupled together at said center tap.

Claim 20

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing analog signals to be amplified, voltage controlled attenuation means, a feedback network, a modulator for converting said analog signals to a pulse width modulated train of pulses, power amplifier means for amplifying said pulse width modulated train of pulses and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator for producing pulse trains, width modulated in accordance with the amplitude of said analog signal, having first and second switching devices, each having an input terminal, an output terminal and a control terminal, together with means for coupling said switching devices together in a non-saturating common terminal differential amplifier configuration, and further including a serrated waveform pulse generator coupled to the control terminal of said first switching device and having a given sampling frequency together with means for coupling said audio signal to the control terminal of said second switching device but not to the control terminal of said first switching device.

Claim 21

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing analog signals to be amplified, voltage controlled attenuation means, a feedback network, a modulator for converting said analog signals to a pulse width modulated train of pulses, power amplifier means for amplifying said pulse width modulated train of pulses and reconstruction filter means for recovering the analog signals from said width modulated trains of pulses: comparator means within said modulator for producing pulse trains, width modulated in accordance with the amplitude of said analog signal, having first and second switching devices, each having an input terminal, an output terminal and a control terminal, together with means for coupling said switching devices together in a non-saturating common terminal differential amplifier configuration, and further including a serrated waveform pulse generator coupled to the control terminal of said first switching device and having a given sampling frequency together with means for coupling said audio signal to the control terminal of said second switching device but not to the control terminal of said first switching device.

Claim 22

The combination as set forth in claim 15 further including a second common terminal non-saturating differential amplifier having input terminals thereof coupled to the output terminals of said first and second switching devices of said first differential amplifier and having a common terminal current source, together with a disable circuit for disabling said second differential amplifier as long as an inhibit signal is applied thereto.

Claim 23

The combination as set forth in claim 15 further including missing pulse detection means having an input circuit for detecting a state of missing pulses within the pulse train produced by said comparator means indicative of clipping of the audio signal being amplified, and for producing an output signal indicative of missing pulse occurrences; and means for coupling said output signal of said missing pulse detection means to said voltage controlled attenuator means for attenuating said audio signal passing therethrough to prevent said clipping.

Claim 24

The combination as set forth in claim 17 wherein said missing pulse detection means further includes a timing circuit for establishing a reference time interval indicative of said state of missing pulses and for producing said output signal only upon the absence of pulses, normally applied to said input circuit of said missing pulse detection means, during a time duration greater than said reference time interval.

Claim 25

The combination as set forth in claim 18 further including switching means for reinitiating timing by said timing circuit upon the application of a pulse applied to the input circuit of said missing pulse detection means.

Claim 26

The combination as set forth in claim 18 wherein said missing pulse detection means further includes an integrating device for producing an increasing signal with time and which functions to produce said output signal upon said increasing signal exceeding a given level and switching means for inhibiting the buildup of said increasing signal upon the detection of a pulse applied to the input circuit of said missing pulse detection means.

Claim 27

The combination as set forth in claim 20 wherein said timing circuit comprises a resistor and reactor having a given time constant proportional to said reference time interval indicative of said state of missing pulses.

Claim 28

The combination as set forth in claim 16 further including a protection circuit for very rapidly disabling said modulator, including a sensing means for sensing excessive audio current being amplified, together with inhibit switching means coupled to said sensing means for generating a fixed interval inhibit signal upon the sensing of excessive audio current by said sensing means, and means for coupling said inhibit signal to said disable circuit of said second differential amplifier.

Claim 29

The combination as set forth in claim 17, 18 or 19 wherein the serrated waveform has an isosceles triangular configuration and peak-to-peak voltage levels which exceed the amplitude of said audio signal until occurrence of over modulation to produce said state of missing pulses.

Claim 30

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing analog signals to be amplified, voltage controlled attenuation means, a feedback network, a modulator for converting said analog signals to a pulse width modulated train of pulses, power amplifier means for amplifying said pulse width modulated train of pulses and reconstruction filter means, said power amplifier means including a push-pull power amplifier having a negative power supply bus and a positive power supply bus and first and second amplifier devices coupled in series across said positive and negative power supply bus, reactance means coupled between said first and second amplifier devices and having a center tap, and push-pull amplifier crossover distortion compensation means comprising: autotransformer means coupled between said center tap of said reactance means and said reconstruction filter, said autotransformer means having a first and second output terminal and a tap; first coupling means for coupling said autotransformer tap to said center tap of said reactance means; second coupling means for coupling said first terminal of said autotransformer means to said reconstruction filter; third coupling means for coupling said second terminal of said autotransformer means to one of said power supply busses via a first diode; fourth coupling means for coupling said second terminal of said autotransformer means to the other power supply bus via a second diode, said first and second diodes being back biased with respect to the polarity of the voltages upon said busses.

Claim 31

In a digital energy conversion high fidelity audio amplifier having an audio signal source for producing analog signals to be amplified, voltage controlled attenuation means, a feedback network, a modulator for converting said analog signals to a pulse width modulated train of pulses, power amplifier means for amplifying said pulse width modulated train of pulses and reconstruction filter means, said power amplifier means including a push-pull power amplifier having a negative power supply bus and a positive power supply bus and first and second amplifier devices coupled in series across said positive and negative power supply bus, reactance means coupled between said first and second amplifier devices and having a center tap, and push-pull amplifier crossover distortion compensation means comprising: autotransformer means coupled between said center tap of said reactance means and said reconstruction filter, said autotransformer means having a first and second output terminal and a tap; first coupling means for coupling said autotransformer tap to said center tap of said reactance means; second coupling means for coupling said first terminal of said autotransformer means to said reconstruction filter; third coupling means for coupling said second terminal of said autotransformer means to one of said power supply busses via a first diode; fourth coupling means for coupling said second terminal of said autotransformer means to the other power supply bus via a second diode, said first and second diodes being back biased with respect to the polarity of the voltages upon said busses.

Claim 32

The combination as set forth in claim 24 further including a third back biased diode coupled across said reactance means and one of said amplifying devices together with a fourth back biased diode coupled across said reactance means and the other of said amplifying devices.

Claim 33

The combination as set forth in claims 24 or 25 wherein said reactance means comprises first and second inductors coupled together at said center tap.

Claim 34

The combination a set forth in claims 1, 2, 3, 7, 15, 16, 17, 18 or 22 wherein said reconstruction filter means includes a low pass filter means for recovering said audio signal amplified by said power amplifier means and notch filter means for eliminating at least the fundamental frequency component of the switching frequency of said power amplifier means.

Claim 35

The combination as set forth in claim 27 further including variable reactor means for tuning at least one section of said notch filter means, and means for coupling said variable reactor means to said feedback network to enable reduction of output distortion by observing the output signal from said audio amplifier while actuating said variable reactor means.

Claim 36

The combination as set forth in claim 28 further including damping means coupled to said variable reactor means for damping the Q of said section of said notch filter to facilitate the observation and correction of said output signal.

Claim 37

The combination as set forth in claim 28 wherein said power amplifier means includes a push-pull power amplifier having a negative power supply bus and a positive power supply bus and first and second amplifier devices coupled in series across said positive and negative power supply bus, first reactance means coupled between said first and second amplifier devices and having a center tap, and push-pull amplifier crossover distortion compensation means comprising: second inductive reactance means coupled between said center tap of said first reactance means and said reconstruction filter, said second inductive reactance means having a first and second terminal and a tap; first coupling means for coupling said tap to said center tap of said first reactance means; second coupling means for coupling said first terminal of said second inductive reactance means to said reconstruction filter; third coupling means for coupling said second terminal of said second inductive reactance means to one of said power supply busses via a first diode; fourth coupling means for coupling said second terminal of said second inductive reactance means to the other power supply bus via a second diode, said first and second diodes being back biased with respect to the polarity of the voltages upon said busses.

Claim 38

The combination as set forth in claim 30 further including a third back biased diode coupled across said first reactance means and one of said amplifying devices together with a fourth back biased diode coupled across said first reactance means and the other of said amplifying devices.

Claim 39

The combination as set forth in claim 31 wherein said first reactance means comprises first and second inductors coupled together at said center tap.

Claim 40

The combination as set forth in claim 27 wherein said reconstruction filter means further includes an R.F. filter.

Claim 41

The combination as set forth in claim 28 wherein said reconstruction filter means further includes an R.F. filter.

Claim 42

The combination as set forth in claim 30 wherein said reconstruction filter means further includes an R.F. filter. .Iadd.

Claim 43

A digital energy conversion audio amplifier, comprising: a feedback network responsive to an analog signal to be amplified; a modulator responsive to said analog signal for converting said analog signals to pulse width-modulated trains of pulses and including first and second switching devices coupled together in a non-saturating common terminal differential amplifier configuration and responsive to said analog signals and a serrated waveform controlling the pulse width modulation of said analog signals, and power amplifier means for amplifying said pulse width-modulated trains of pulses; reconstruction filter means responsive to the amplified trains of pulses for recovering the analog signals; means for coupling a signal from said reconstruction filter means to said feedback network to eliminate closed loop distortion; and further comprising voltage controlled attenuator means responsive to an analog signal to be amplified and proving an analog output representative thereof and distortion detection means responsive to the pulse width-modulated trains of pulses to detect pulses missing therefrom and controlling said voltage controlled attenuator to attenuate the analog signal to be amplified. .Iaddend. .Iadd.37. The digital energy conversion audio amplifier as claimed in claim 36, further comprising means for monitoring the amplified trains of pulses from said power amplifier means and disabling said modulator upon detection of an excessive signal level in said power amplifier means. .Iaddend. .Iadd.38. A digital energy conversion audio amplifier, comprising: a feedback network responsive to an analog signal to be amplified; a modulator responsive to said analog signal for converting said analog signals to pulse width-modulated trains of pulses and including first and second switching devices coupled together in a non-saturating common terminal differential amplifier configuration and responsive to said analog signals and a serrated waveform controlling the pulse width modulation of said analog signals, and power amplifier means for amplifying said pulse width-modulated trains of pulses; reconstruction filter means responsive to the amplified trains of pulses for recovering the analog signals; means for coupling a signal from said reconstruction filter means to said feedback network to eliminate closed loop distortion; and further comprising means for monitoring the amplified trains of pulses from said power amplifier means and disabling said modulator upon detection of an excessive signal level in said power amplifier means. .Iaddend. .Iadd.39. A digital energy conversion amplifier comprising the combination of: audio signal source means for providing an audio frequency analog signal to be amplified; a feedback network responsive to the audio frequency analog signal to be amplified; modulator means responsive to the feedback network for providing non-saturated, power amplified, out-of-phase, pulse width-modulated trains of pulses; low-pass filter means for recovering said audio signal as amplified; and notch filter means responsive to the power amplified trains of pulses and connected to said feedback network prior to said low-pass filter means, said notch filter means eliminating at least the fundamental frequency component of the switching frequency of said power amplified, out-of-phase pulse-width modulated trains of pulses. .Iaddend. .Iadd.40. The digital energy conversion audio amplifier as claimed in claim 39, wherein said notch filter means includes variable reactor means. .Iaddend. .Iadd.41. The digital energy conversion audio amplifier as claimed in claim 40, further including damping means coupled to said variable reactor means for damping the Q of said section of said notch filter. .Iaddend.