Apparatus for and method of speech digitizing
AssigneeEricsson Inc.
InventorPaul W. Dent
Life of this patent
Estimating the term…
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.
Claims32
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.
An analog to digital conversion circuit comprising:
- 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.
A circuit for converting a plurality of binary coded numerical signal samples to an analog signal waveform, said circuit comprising:
- 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.
A digital-to-analog conversion circuit comprising:
- 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.
A method of converting an analog waveform signal to a digital waveform signal, said method comprising the steps of:
- 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.
A method of converting a plurality of binary coded numerical signal samples to an analog signal waveform, said method comprising the steps of:
- 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.
A circuit for converting a plurality of binary coded numerical signal samples to an analog signal waveform, said circuit comprising:
- 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.
Dependencies are inferred from the claim text.