Instrumentation amplifier with improved AC common mode rejection performance

A two op-amp instrumentation amplifier having a first op-amp and a second op-amp coupled in series between an input and- an output of the instrumentation amplifier, the two op-amp instrumentation amplifier comprising a first op-amp with a frequency response characterized by at least two low frequency poles and at least one zero, the first op amp circuitry comprising:

• a first gain stage having a first input coupled to an inverting input of the first op-amp, a second input coupled to a noninverting input of the first op-amp, and a first stage output;
• a second gain stage having an input coupled to the first stage output, and a second stage output;
• a third gain stage having a first input coupled to the inverting input of the first op-amp, a second input coupled to the noninverting input of the first op-amp, and an output;
• and
• a summing junction coupled to the outputs of the second and third gain stages for summing the outputs of signals received therethrough, and coupled to an output of the first op-amp.

A two op-amp instrumentation amplifier having a first op-amp and a second op-amp coupled in series between an input and an output of the instrumentation amplifier, the two op-amp instrumentation amplifier comprising a first op-amp with a frequency response characterized by at least two low frequency poles and at least one zero,

• wherein the two op-amp instrumentation amplifier having a reference voltage input and an amplifier output, a second op-amp with both inverting and non-inverting inputs and an output, the first and second op-amps being coupled in series between the amplifier inputs and the amplifier output, the first op-amp of the two op-amp instrumentation amplifier further comprising:
• a first resistor coupled between the reference voltage input and the inverting input of the first op-amp;
• a second resistor coupled between the inverting input of the first op-amp and the output of the first op-amp;
• a third resistor coupled between the output of the first op-amp and an inverting input of the second op-amp;
• a fourth resistor coupled between the inverting input of the second op-amp and the output of the second op-amp;
• a negative input coupled to the noninverting input of the first op-amp;
• and
• a positive input coupled to the noninverting input of the second op-amp.

A two op-amp instrumentation amplifier having an inverting amplifier input a noninverting amplifier input, a reference voltage input and an amplifier output, a first op-amp with both inverting and non-inverting inputs and an output, and a second op-amp with both inverting and non-inverting inputs and an output, the first and second op-amps being coupled in series between the amplifier inputs and the amplifier output, the two op-amp instrumentation amplifier comprising the first op-amp configured to comprise:

• a first gain stage having a first input coupled to the inverting input of the first op-amp, a second input coupled to the noninverting input of the first op-amp, and a first stage output;
• a second gain stage having an input coupled to the first stage output, and a second stage output;
• a third gain stage having a first input coupled to the inverting input of the first op-amp, a second input coupled to the noninverting input of the first op-amp, and an output;
• and
• a summing junction coupled to the outputs of the second and third gain stages for summing the outputs of signals received therethrough, and coupled to the output of the first operational amplifier.

A two op-amp instrumentation amplifier having an inverting amplifier input a noninverting amplifier input, a reference voltage input and an amplifier output, a first op-amp with both inverting and non-inverting inputs and an output, and a second op-amp with both inverting and non-inverting inputs and an output, the first and second op-amps being coupled in series between the amplifier inputs and the amplifier output, the two op-amp instrumentation amplifier comprising the first op-amp configured to comprise:

• a first gain stage having a first input coupled to the inverting input of the first op-amp, a second input coupled to the noninverting input of the first op-amp, and a first stage output;
• a second gain stage having an input coupled to the first stage output, and a second stage output;
• a third gain stage having a first input coupled to the inverting input of the first op-amp, a second input coupled to the noninverting input of the first op-amp, and an output;
• and
• a summing junction coupled to the outputs of the second and third gain stages for summing the outputs of signals received therethrough, and coupled to the output of the first operational amplifier, further comprising:
• a first resistor coupled between the reference voltage input and the inverting input of the first op-amp;
• a second resistor coupled between the inverting input of the first op-amp and the output of the first op-amp;
• a third resistor coupled between the output of the first op-amp and an inverting input of the second op-amp;
• a fourth resistor coupled between the inverting input of the second op-amp and the output of the second op-amp;
• a negative coupled to the noninverting input of the first op-amp;
• and
• a positive coupled to the noninverting input of the second op-amp.