Spread spectrum chopping for sigma delta modulators
AssigneeAnalog Devices International Unlimited Company
InventorsRoberto Sergio Matteo Maurino, Bhargav E. Vyas, Ayesha Shaik
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Abstract
Chopping techniques that suppress fold-back into the signal band and spreads the offset across the spectrum are described. By using various techniques, chopping may be performed with a variable frequency clock to spread the offset across the signal spectrum. Spreading the offset across the signal spectrum means that there are no longer large spurious tones at a few frequencies.
Claims20
An analog-to-digital converter (ADC) circuit to generate a digital output signal, the ADC circuit comprising:
- an oversampled ADC circuit having an input coupled to receive an analog input signal and generate a first digital output signal, the oversampled ADC including:
- a chop switch that receives and is controlled by a variable frequency chop signal;
- and
- a chop signal generating circuit to generate the variable frequency chop signal;
- a sample rate converter circuit to receive the first digital output signal at a first sample rate and generate a second digital output signal at a second sample rate;
- and
- a digital filter circuit to process the second digital output signal and generate a filtered digital output signal.
A method of operating an analog-to-digital converter (ADC) circuit to generate a digital output signal, the method comprising:
- receiving an analog input signal at a summing node of a sigma-delta (SD) ADC circuit, wherein the SD ADC circuit includes an integrator circuit having an amplifier circuit and a chop switch coupled to an input of the amplifier circuit;
- receiving, using the integrator circuit, an output of the summing node;
- generating a variable frequency chop signal and operating the chop switch at the variable frequency chop signal;
- receiving a first digital output signal of the SD ADC circuit at a first sample rate and generating a second digital output signal at a second sample rate;
- and
- processing the second digital output signal and generating a filtered digital output signal.
An analog-to-digital converter (ADC) circuit to generate a digital output signal, the ADC circuit comprising:
- a sigma-delta (SD) ADC circuit having an input coupled to receive an analog input signal and generate a digital output signal, the SD ADC including:
- an integrator circuit including an amplifier circuit and a chop switch, the chop switch coupled to an input of the amplifier circuit, wherein the chop switch receives and is controlled by a variable frequency chop signal;
- and
- means for generating the variable frequency chop signal;
- and
- a digital filter circuit to process a representation of the digital output signal and generate a filtered digital output signal.
Dependencies are inferred from the claim text.