Capacitively coupled chopper amplifier

A capacitively coupled chopper amplifier comprising:

• an input chopping switch to switch first and second inputs between first and second outputs according to a mode input;
• first and second series input capacitors coupled to the input chopping switch;
• a first differential amplifier coupled to first and second series input capacitors;
• an amplifier output chopping switch coupled to the first differential amplifier and operable, according to a mode input, to switch first and second inputs between first and second outputs or to disconnect the first and second inputs from the first and second outputs;
• a second differential amplifier coupled to the amplifier output chopping switch;
• a feedback chopping switch coupled to the second differential amplifier and operable, according to a mode input, to switch first and second inputs between first and second outputs or to disconnect the first and second inputs from the first and second outputs;
• first and second feedback capacitors coupled to the feedback chopping switch, the first feedback capacitor coupled to the first series input capacitor and the second feedback capacitor coupled to the second series input capacitor;
• a feedback dual pole switch to switch first and second inputs between first and second outputs according to a mode input, the first and second inputs coupled to the second differential amplifier, the first and second outputs coupled to the feedback chopping switch;
• an output capacitor coupled to the feedback chopping switch first and second inputs;
• a correction dual pole switch to switch first and second inputs between first and second outputs according to a mode input, the first and second inputs coupled to the feedback chopping switch;
• a correction capacitor coupled to the first and second outputs of the correction dual pole switch;
• a charging dual pole switch to switch first and second inputs between first and second outputs according to a mode input, the first and second outputs coupled to the correction dual pole switch, the first and second inputs for receiving a voltage for charging the correction capacitor, and
• a phase generator having a plurality of outputs and generating six phases, the six phases being a first zeroing phase, a first charge transfer phase, a first chopping phase, a second zeroing phase, a second charge transfer phase and a second chopping phase, the plurality of outputs being coupled to the mode inputs of the input chopping switch, zeroing chopping switch, amplifier chopping switch, feedback chopping switch, feedback dual pole switch, correction dual pole switch and charging dual pole switch, the phase generator for generating mode control output signals for configuring the modes of each of the input chopping switch, zeroing chopping switch, amplifier chopping switch, feedback chopping switch, feedback dual pole switch, correction dual pole switch and charging dual pole switch based on the six phases.

A method of operating a capacitively coupled chopper amplifier, the capacitively coupled chopper amplifier including:

• an input chopping switch having first and second inputs, first and second outputs and a mode input, the first and second inputs being the inputs of the capacitively coupled chopper amplifier, in a first mode connecting the first input to the first output and the second input to the second output and in a second mode connecting the first input to the second output and the second input to the first output;
• first and second series input capacitors, each having an input and an output, the first series input capacitor input being coupled to the input chopping switch first output and the second series input capacitor input being coupled to the input chopping switch second output;
• a zeroing chopping switch having first, second and third inputs, first and second outputs and a mode input, in a first mode connecting the first input to the first output and the second input to the second output and in a second mode connecting the third input to the first and second outputs, the first input coupled to the first series input capacitor output, the second input coupled to the second series input capacitor output and the third input for receiving a common mode voltage;
• a first differential amplifier having noninverting and inverting inputs and noninverting and inverting outputs, the noninverting input coupled to the first series input capacitor output and the inverting input coupled to the second series input capacitor output;
• an amplifier output chopping switch having first and second inputs, first and second outputs and a mode input, in a first mode connecting the first input to the first output and the second input to the second output, in a second mode connecting the first input to the second output and the second input to the first output, and in a third mode disconnecting the first and second inputs from the first and second outputs, the first input coupled to the first differential amplifier inverting output and the second input coupled to the first differential amplifier noninverting output;
• a second differential amplifier having noninverting and inverting inputs and noninverting and inverting outputs, the inverting input coupled to the amplifier chopping switch first output and the noninverting input coupled to the amplifier chopping switch second output, the noninverting and inverting outputs providing the outputs of the capacitively coupled chopper amplifier;
• a feedback chopping switch having first and second inputs, first and second outputs and a mode input, in a first mode connecting the first input to the first output and the second input to the second output, in a second mode connection the first input to the second output and the second input to the first output and in a third mode disconnecting the first and second inputs from the first and second outputs, the first input coupled to the second amplifier noninverting output and the second input coupled to the second amplifier inverting output;
• first and second feedback capacitors, each having an input and an output, the first feedback capacitor input being coupled to the feedback chopping switch first output and the second feedback capacitor input being coupled to the feedback chopping switch second output, the first feedback capacitor output being coupled to the second series input capacitor output and the second feedback capacitor output being coupled to the first series input capacitor output;
• a feedback dual pole switch having first and second inputs, first and second outputs and a mode input, the first input coupled to the noninverting output of the second differential amplifier, the second input coupled to the inverting output of the second differential amplifier, the first output coupled to the feedback chopping switch first input and the second output coupled to the feedback chopping switch second input, in a first mode connecting the first and second inputs to the first and second outputs, respectively, and in a second mode disconnecting the first and second inputs from the first and second outputs;
• an output capacitor having a first connection coupled to the feedback chopping switch first input and a second connection coupled to the feedback chopping switch second input;
• a feedback capacitor discharge dual pole switch having an input, first and second outputs and a mode input, the first output coupled to the second feedback capacitor input and the second output coupled to the first feedback capacitor input, the input for receiving a common mode voltage, in a first mode connecting the input to the first and second outputs and in a second mode disconnecting the input from the first and second outputs;
• an input capacitor dual pole switch having an input, first and second outputs and a mode input, the first output coupled to the first series input capacitor output and the second output coupled to the second series input capacitor output, in a first mode connecting the input to the first and second outputs and in a second mode disconnecting the input from the first and second outputs;
• and
• a correction dual pole switch having first and second inputs, first and second outputs and a mode input, the first input coupled to the feedback chopping switch first input and the second input coupled to the feedback chopping switch second input, in a first mode connecting the first and second inputs to the first and second outputs, respectively, and in a second mode disconnecting the first and second inputs from the first and second outputs;
• a correction capacitor having a first connection coupled to the first output of the correction dual pole switch and a second connection coupled to the second output of the correction dual pole switch;
• and
• a charging dual pole switch having first and second inputs, first and second outputs and a mode input, the first output coupled to the first output of the correction dual pole switch, the second output coupled to the second output of the correction dual pole switch, the first input and the second input for receiving a voltage for charging the correction capacitor, in a first mode connecting the first and second inputs to the first and second outputs, respectively, and in a second mode disconnecting the first and second inputs from the first and second outputs,
• a phase generator having a plurality of mode control outputs and generating six phases, the six phases being a first zeroing phase, a first charge transfer phase, a first chopping phase, a second zeroing phase, a second charge transfer phase and a second chopping phase, the plurality of outputs being coupled to the mode inputs of the input chopping switch, zeroing chopping switch, amplifier output chopping switch, feedback chopping switch, feedback capacitor discharge dual pole switch, input capacitor dual pole switch, feedback dual pole switch, correction dual pole switch and charging dual pole switch,
• the method comprising the steps of:
• placing the input chopping switch in the first mode during the first zeroing phase, the second charge transfer phase and the second chopping phase and in the second mode during the first charge transfer phase, the first chopping phase and the second zeroing phase,
• placing the zeroing chopping switch in the first mode during the first chopping phase and the second chopping phase and in the second mode during the first zeroing phase, the first charge transfer phase, the second zeroing phase and the second charge transfer phase,
• placing the amplifier output chopping switch in the first mode during the second chopping phase, in the second mode during the first chopping phase and in the third mode during first zeroing phase, the first charge transfer phase, the second zeroing phase and the second charge transfer phase,
• placing the feedback chopping switch in the first mode during the second charge transfer phase and the second chopping phase, the second mode during the first charge transfer phase and the first chopping phase and the third mode during the first zeroing phase and the second zeroing phase,
• placing the feedback capacitor discharge dual pole switch in the first mode during the first zeroing phase and the second zeroing phase and in the second mode during the first charge transfer phase, the first chopping phase, the second charge transfer phase and the second chopping phase,
• placing the input capacitor dual pole switch in the first mode during the first zeroing phase and the second zeroing phase and in the second mode during the first charge transfer phase, the first chopping phase, the second charge transfer phase and the second chopping phase,
• placing the feedback dual pole switch in the first mode during the first chopping phase and the second chopping phase and in the second mode during the first zeroing phase, the first charge transfer phase, the second zeroing phase and the second charge transfer phase,
• placing the correction dual pole switch in the first mode during the first zeroing phase, the first charge transfer phase, the second zeroing phase and the second charge transfer phase and in the second mode during the first chopping phase and the second chopping phase, and
• placing the charging dual pole switch in the first mode during the first chopping phase and the second chopping phase and in the second mode during the first zeroing phase, the first charge transfer phase, the second zeroing phase and the second charge transfer phase.