Programmable gain amplifier with amplifier common mode sampling system

A programmable gain amplifier (“PGA”), comprising:

• a differential amplifier having a pair of inputs and a pair of outputs,
• a pair of input capacitors having output terminals connected respectively to inputs of the differential amplifier,
• a pair of feedback capacitors connected respectively between outputs of the differential amplifier and corresponding inputs of the differential amplifier,
• a first cross-coupled chop circuit connecting the input capacitors to respective input terminals of the PGA,
• a second cross-coupled chop circuit connecting the output terminals of the differential amplifier to respective output terminals of the PGA, and
• a voltage source coupled to input terminals of the input capacitors via respective switches, having a voltage set to a common mode voltage of an input signal to be presented to the PGA.

A programmable gain amplifier (“PGA”), comprising:

• a differential amplifier having a pair of inputs and a pair of outputs,
• a pair of input capacitors connected respectively to inputs of the differential amplifier,
• a pair of feedback capacitors connected respectively between outputs of the differential amplifier and corresponding inputs of the differential amplifier,
• a first chop circuit connecting the input capacitors to respective input terminals of the PGA,
• a second chop circuit connecting the output terminals of the differential amplifier to respective output terminals of the PGA, and
• means for sampling voltages across the input capacitors when the second chop circuit is disabled, the sampled voltages corresponding to a difference between a common mode voltage of signals input to the PGA and a common mode voltage of the differential amplifier.

A programmable gain amplifier (“PGA”), comprising:

• a differential amplifier having a pair of inputs and a pair of outputs,
• a pair of input capacitors connected respectively to inputs of the differential amplifier,
• a pair of feedback capacitors connected respectively between outputs of the differential amplifier and corresponding inputs of the differential amplifier,
• a first chop circuit connecting the input capacitors to respective input terminals of the PGA,
• a second chop circuit connecting the output terminals of the differential amplifier to respective output terminals of the PGA, and
• means for presenting a voltage at input terminals of the input capacitors corresponding to a common mode voltage of signals input to the PGA when the second chop circuit is disabled, and
• means for presenting a voltage at input terminals of the amplifier corresponding to an offset-compensated common mode voltage of the amplifier when the second chop circuit is disabled.

A method of controlling a chopped capacitor-based programmable gain amplifier, comprising:

• in a common mode sampling phase of operation, sampling a voltage across input capacitors of the PGA corresponding to a difference between a common mode voltage of input signals to be input to the PGA and a common mode voltage of a differential amplifier within the PGA,
• in a first chop phase of operation, controlling chop circuits within the PGA to propagate a differential input signal from input terminals of the PGA to output terminals of the PGA, the input signal having a first orientation with respect to the differential amplifier,
• in a second chop phase of operation, controlling the chop circuits within the PGA to propagate the differential input signal from the input terminals of the PGA to the output terminals of the PGA, the input signal having a second orientation with respect to the differential amplifier inverse of the first orientation,
• wherein sampling is terminated at an end of the first phase.