Multi-level pulse width modulation in digital system
First Claim
1. Apparatus for controlling switching circuitry for generating an analog output from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the apparatus including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit values carried by the first digital signal, and further comprising:
- pulse width modulation (PWM) circuitry operative to generate a pulse width modulated signal based on the first digital sub-signal; and
switch control circuitry under the control of the pulse width modulated signal and the second digital sub-signal and operative via the switching circuitry to produce the analog output.
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Abstract
A multi-level pulse width modulation (multi-level PWM) technique uses multiple voltage levels and/or multiple output channels to obtain improved resolution (also referred to as dynamic range) over ordinary PWM-based digital systems, in particular digital audio systems. A digital audio signal is converted to either (1) an N-level PWM signal which is output to a single channel including a filter and loudspeaker, (2) N components of an N-level PWM signal output to N corresponding channels, (3) some number of multi-level signals output to multiple channels or (4) some number of PWM signals output to multiple channels. The digital audio signal can also be divided into different frequency bands to be processed separately and output to different sets of loudspeakers, wherein fewer low frequency loudspeakers can be used than high frequency loudspeakers to produce equal effective resolution for the output of all frequency bands. The multi-level PWM technique can also be adapted to control the output of other types of PWM-based systems when greater resolution is desired.
27 Citations
141 Claims
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1. Apparatus for controlling switching circuitry for generating an analog output from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the apparatus including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit values carried by the first digital signal, and further comprising:
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pulse width modulation (PWM) circuitry operative to generate a pulse width modulated signal based on the first digital sub-signal; and
switch control circuitry under the control of the pulse width modulated signal and the second digital sub-signal and operative via the switching circuitry to produce the analog output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. Apparatus for controlling switching circuitry for generating an analog output from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the apparatus including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit values carried by the first digital signal, the analog output being generated by additively combining a plurality of analog component outputs from a corresponding plurality of channels, each analog component output being generated from a corresponding one of a plurality of electrical signals, the switching circuitry including a plurality of switches, each switch being associated with a corresponding one of the channels, the switch for the first channel being operative in response to assertion of a pulse width modulated signal to generate a corresponding one of the electrical signals, the switch for each of the other channels being operative based on assertion of a corresponding one of switch control signals to generate a predetermined level on the electrical signal of the corresponding channel, and the apparatus further comprising:
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pulse width modulation (PWM) circuitry operative to generate the pulse width modulated signal based on the first digital sub-signal; and
switch control circuitry operative to assert different numbers of the switch control signals based on the second digital sub-signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. Apparatus for controlling switching circuitry for generating an analog output from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the apparatus including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit values carried by the first digital signal, the analog output being generated by additively combining analog component outputs from first and second channels, the analog component output of the second channel being generated from a multi-level electrical signal, the switching circuitry including a set of switches each operative based on assertion of a corresponding one of first set of control signals for the second channel to provide one of a set of distinct levels of the multi-level electrical signal of the second channel, and the apparatus further comprising:
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pulse width modulation (PWM) circuitry operative to generate a pulse width modulated signal, the pulse width modulated signal being based on the first digital sub-signal and operative via the switching circuitry to generate an electrical signal from which the analog component output of the first channel is generated; and
switch control circuitry including a level selector associated with the second channel operative to assert each of the first set of control signals of the second channel based on the second digital sub-signal and a maximum-width-pulse signal, the maximum-width-pulse signal establishing the maximum permissible pulse duration in a sampling cycle for the pulse width modulated signal. - View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59)
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60. A digital audio system for generating an acoustic audio signal from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the digital audio system including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit audio values carried by the first digital signal, the acoustic audio signal being generated from a multi-level electrical signal, and the system further comprising:
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a loudspeaker;
a low-pass filter coupled to the loudspeaker;
switching circuitry coupled to the low-pass filter, the switching circuitry including a plurality of switches each operative in response to assertion of a corresponding one of switch control signals to provide one of a set of distinct levels of a multi-level electrical signal, the multi-level electrical signal being provided to the low-pass filter;
pulse width modulation (PWM) circuitry operative to generate a pulse width modulated signal based on the first digital sub-signal; and
switch control circuitry including a level selector operative to assert each of the switch control signals based on the pulse width modulated signal, a maximum-width-pulse signal and the second digital sub-signal, the maximum-width-pulse signal establishing the maximum permissible pulse duration in a sampling cycle for the pulse width modulated signal. - View Dependent Claims (61, 62, 63, 64, 65, 66)
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67. A digital audio system for generating an acoustic audio signal from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the digital audio system including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit audio values carried by the first digital signal, the acoustic audio signal being generated by additively combining a plurality of acoustic audio component signals from a corresponding plurality of channels, each acoustic audio component signal being generated from a corresponding one of a plurality of pulse electrical signals which include fixed-width pulse electrical signals and a variable-width pulse electrical signal, and the system further comprising:
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a plurality of loudspeakers each associated with a corresponding one of the channels;
a plurality of low-pass filters each coupled to a corresponding one of the loudspeakers;
switching circuitry coupled to the low-pass filters, the switching circuitry including a plurality of switches, each switch being associated with a corresponding one of the channels, the switch for one of the channels being operative on assertion of a pulse width modulated signal to generate the variable-width pulse electrical signal, the switch for each of the other channels being operative on assertion of a corresponding one of switch control signals and a maximum-width-pulse signal to generate the corresponding fixed-width pulse electrical signal, the maximum-width-pulse signal establishing the maximum permissible pulse duration in a sampling cycle for the pulse width modulated signal, each pulse electrical signal being provided to the corresponding low-pass filter;
pulse width modulation (PWM) circuitry operative to generate the pulse width modulated signal based on the first digital sub-signal; and
switch control circuitry including an encoder operative to assert different numbers of the switch control signals based on the second digital sub-signal. - View Dependent Claims (68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81)
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82. A digital audio system for generating an acoustic audio signal from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the digital audio system including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit audio values carried by the first digital signal, the acoustic audio signal being generated by additively combining acoustic audio component signals from first and second channels, the acoustic audio component signal of the second channel being generated from a multi-level electrical signal, and the system further comprising:
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a plurality of loudspeakers each associated with a corresponding one of the channels;
a plurality of low-pass filters each coupled to a corresponding one of the loudspeakers;
switching circuitry including a set of switches each operative based on assertion of a corresponding one of first set of control signals for the second channel to provide one of a set of distinct levels of the multi-level electrical signal of the second channel;
pulse width modulation (PWM) circuitry operative to generate a pulse width modulated signal, the pulse width modulated signal being based on the first digital sub-signal and operative via the switching circuitry to generate an electrical signal from which the acoustic audio component signal of the first channel is generated;
each electrical signal being provided to its corresponding low-pass filter; and
switch control circuitry including a level selector associated with the second channel operative to assert each of the first set of control signals of the second channel based on the second digital sub-signal and a maximum-width-pulse signal, the maximum-width-pulse signal establishing the maximum permissible pulse duration in a sampling cycle for the pulse width modulated signal. - View Dependent Claims (83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102)
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103. Apparatus for controlling switching circuitry for generating an analog output from a digital signal the digital signal carrying multi-bit values at a sampling rate, the apparatus including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit values carried by the first digital signal, the analog output being generated by additively combining analog component outputs from first and second channels, the analog component output of the first channel being generated from an electrical signal of the first channel, the switching circuitry including a switching stage of the first channel operative in response to assertion of a pulse width modulated signal of the first channel to provide one of two predetermined levels of the electrical signal of the first channel, the analog component output of the second channel being generated from an electrical signal of the second channel, the switching circuitry further including a switching stage of the second channel operative in response to assertion of a pulse width modulated signal of the second channel to provide one of two predetermined levels of the electrical signal of the second channel, and the apparatus further comprising pulse width modulation (PWM) circuitry including
a PWM circuitry of the first channel operative to generate the pulse width modulated signal of the first channel, the pulse width modulated signal of the first channel being based on the first digital sub-signal and operative via the switching stage of the first channel to generate the electrical signal from which the analog component output of the first channel is generated and a PWM circuitry of the second channel operative to generate the pulse width modulated signal of the second channel, the pulse width modulated signal of the second channel being based on the second digital sub-signal and operative via the switching stage of the second channel to generate the electrical signal from which the analog component output of the second channel is generated.
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125. A digital audio system for generating an acoustic audio signal from a digital signal, the digital signal carrying multi-bit values at a sampling rate, the digital audio system including a first digital signal derived from the digital signal, the first digital signal including first and second digital sub-signals carrying respective least and most significant components of the multi-bit audio values carried by the first digital signal, the acoustic audio signal being generated by additively combining acoustic audio component signals from first and second channels, the acoustic audio component signal of the first channel being generated from an electrical signal of the first channel, the acoustic audio component signal of the second channel being generated from an electrical signal of the second channel, and the system further comprising:
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a plurality of loudspeakers each associated with a corresponding one of the channels;
a plurality of low-pass filters each coupled to a corresponding one of the loudspeakers;
switching circuitry including a switching stage of the first channel operative in response to assertion of a pulse width modulated signal of the first channel to provide one of the two predetermined levels of the electrical signal of the first channel;
the switching circuitry further including a switching stage of the second channel operative in response to assertion of a pulse width modulated signal of the second channel to provide one of the two predetermined levels of the electrical signal of the second channel, each electrical signal being provided to its corresponding low-pass filter; and
pulse width modulation (PWM) circuitry includinga PWM circuitry of the first channel operative to generate the pulse width modulated signal of the first channel, the pulse width modulated signal of the first channel being based on the first digital sub-signal and operative via the switching stage of the first channel to generate the electrical signal from which the acoustic audio component signal of the first channel is generated and a PWM circuitry of the second channel operative to generate the pulse width modulated signal of the second channel, the pulse width modulated signal of the second channel being based on the second digital sub-signal and operative via the switching stage of the second channel to generate the electrical signal from which the acoustic audio component signal of the second channel is generated. - View Dependent Claims (126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141)
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Specification