Apparatus for and method of speech digitizing
First Claim
1. A circuit for converting an analog waveform signal to a digital waveform signal, said circuit comprising:
- first integrator means for generating an integrated signal;
means for comparing said analog waveform signal with said integrated signal and for registering a series of increment/decrement values, one value per predetermined interval;
means for setting a step sign of said integrated signal based on a most recent of said registered increment/decrement values;
syllabic filter means for accumulating a series of registered increment/decrement values in a second, leaky digital integrator in order to select a step magnitude; and
decimation filter means for processing said step sign and said step magnitude to generate a sequence of binary coded digital signals representative of said analog waveform signal.
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Abstract
A speech encoder converts analog speech signals into a stream of binary coded speech samples. A circuit for performing analog to digital conversion compares an input speech signal with a signal from a digital integrator. Based on the comparison a series of decisions are registered which indicate a step sign of the input signal. A syllabic filter generates a step magnitude according to the registered decisions. The step sign and step magnitude are combined providing a sign/magnitude representation of the input signal. When the sign/magnitude representation is integrated digitally in a decimation filter a digital representation of the analog signal is formed. A speech decoder, the antithesis of the encoder, converts binary coded speech samples into an analog waveform in a manner opposite to the A/D conversion method.
92 Citations
32 Claims
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1. A circuit for converting an analog waveform signal to a digital waveform signal, said circuit comprising:
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first integrator means for generating an integrated signal; means for comparing said analog waveform signal with said integrated signal and for registering a series of increment/decrement values, one value per predetermined interval; means for setting a step sign of said integrated signal based on a most recent of said registered increment/decrement values; syllabic filter means for accumulating a series of registered increment/decrement values in a second, leaky digital integrator in order to select a step magnitude; and decimation filter means for processing said step sign and said step magnitude to generate a sequence of binary coded digital signals representative of said analog waveform signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An analog to digital conversion circuit comprising:
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a comparator for registering a series of decisions at regular intervals; an input for an analog signal connected by a series capacitor to a first input of said comparator, second input of said comparator being connected to a reference voltage source; and at least one pulse width modulated current source controlled by the output of said comparator, the current output pulse from said current source also being connected to said first comparator input. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A circuit for converting a plurality of binary coded numerical signal samples to an analog signal waveform, said circuit comprising:
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means for interpolating between successive binary coded numerical signal samples to produce N interpolated samples for each binary coded numerical signal sample; means for comparing said interpolated samples with values in a digital integrator and for registering a series of decisions; means for modifying said digital integrator values according to said decisions by a step sign; syllabic filter means for generating a step magnitude for modifying said digital integrator values depending on a successive number of said decisions; leaky analog integrator means for receiving said step sign and said step magnitude and for generating an analog signal described numerically by said digital integrator values; and means for filtering said analog signal to produce an analog waveform corresponding to said binary coded numerical signal samples. - View Dependent Claims (22, 23, 24, 25, 26, 27)
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28. A digital-to-analog conversion circuit comprising:
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means for receiving a companded delta-modulation bit stream; syllabic filter means for generating a plurality of variable step magnitudes based on a successive number of bits in said bit stream; at least two variable pulse width current sources controlled by separate digits of said variable step magnitudes; integrator means for integrating current pulses from said at least two current sources to generate an analog output signal; and means for filtering said analog output signal to produce an analog waveform corresponding to said bit stream. - View Dependent Claims (29)
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30. A method of converting an analog waveform signal to a digital waveform signal, said method comprising the steps of:
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generating an integrated signal by integrating a series of step inputs; comparing said analog waveform signal with said integrated signal and registering a series of decisions, one decision per predetermined interval; setting a step sign for said integrated signal based on a most recent of said registered decisions; selecting a step magnitude based on said registered decisions; and decimating said step sign and said step magnitude to generate a sequence of binary coded digital signals representative of said analog waveform signal dependent on all of said sequentially produced step magnitudes.
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31. A method of converting a plurality of binary coded numerical signal samples to an analog signal waveform, said method comprising the steps of:
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interpolating between successive binary coded numerical signal samples to produce N interpolated samples for each binary coded numerical signal sample; comparing said interpolated samples with values in a digital integrator and registering a series of step sign decisions; modifying said digital integrator values according to said decisions by a step sign and step magnitude; generating a step magnitude for modifying said digital integrator values depending on a successive number of said decisions; processing said step sign and said step magnitude and generating therefrom an analog signal described numerically by said digital integrator values; and filtering said analog signal to produce an analog waveform corresponding to said binary coded numerical signal samples.
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32. A circuit for converting a plurality of binary coded numerical signal samples to an analog signal waveform, said circuit comprising:
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means for interpolating between successive binary coded numerical signal samples to produce N interpolated samples for each binary coded numerical signal sample; means for comparing said interpolated samples with values in a digital integrator and for registering a series of decisions; means for modifying said digital integrator values according to said decisions by a step sign; syllabic filter means for accumulating said series of decisions in a leaky digital integrator in order to select a step magnitude; and leaky analog integrator means for receiving said step sign and said step magnitude and for generating an analog signal described numerically by said digital integrator values; and means for filtering said analog signal to produce an analog waveform corresponding to said binary coded numerical signal samples.
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Specification