Method and apparatus for mixed analog and digital processing of delta modulated pulse streams including digital-to-analog conversion of a digital input signal

A digital to analog converter for converting a digital signal having a plurality of bits, comprising:

• a sigma-delta modulator for encoding an analog reference signal to produce a sigma-delta modulated pulse stream reference signal;
• a delta adder for modulating the sigma-delta modulated pulse stream reference signal with a digital input signal to produce a digital sigma-delta modulated pulse density stream output signal;
• and
• a low pass filter for demodulating the digital sigma-delta modulated pulse density stream output signal to produce an analog output signal.

An attenuator circuit for attenuating an input signal in accordance with the state of the bits of a digital control signal, comprising:

• a sigma-delta modulator for encoding an analog input signal to produce a sigma-delta modulated pulse stream input signal;
• a delta adder for modulating the sigma-delta modulated pulse stream input signal with the digital control signal to produce a digital sigma-delta modulated pulse density stream output signal;
• and
• a low pass filter for demodulating the digital sigma-delta modulated pulse density stream output signal to produce an analog output signal.

A digital processing circuit comprising:

• a source for producing a sigma-delta modulated pulse density stream first input signal;
• a first node for receiving said sigma-delta modulated pulse first input signal;
• a second node for receiving a digital second input signal;
• a third node for receiving a digital third input signal;
• a first signal modulator connected to receive said first and second input signals and for modulating the first input signal with the second input signal to produce an intermediate sigma-delta modulated output pulse density stream;
• and a second signal modulator connected to receive said intermediate sigma-delta modulated output pulse density stream and third input signals and for modulating said intermediate signal with said third input signal to produce an output sigma-delta modulated output pulse density stream.

A digital processing circuit for converting a digital input signal having a plurality of weighted bits into a pulse density serial signal, comprising:

• a source for producing a sigma-delta modulated pulse density stream first input signal;
• a plurality of switches operated to select between a first and a second pole in accordance with a state of a respective weighted bit of said digital input signal;
• said first pole being connected to receive the sigma-delta modulated pulse density first input signal;
• said second pole being connected to receive a delta idle sequence second input signal;
• a plurality of delta adder circuits, each associated with a respective weighted bit of said digital input signal, said adder circuits being connected in series to add the successive outputs of said plurality of switches to the delta modulated second input signal to produce a sigma-delta modulated output pulse density stream;
• and a signal modulator connected to receive said first and second input signals and for modulating the first input signal with the second input signal to produce the sigma-delta modulated output pulse density stream.