原文：Instrumentation Amplifier with DC Rejection Reference Design
Figure 2 shows the schematic of the instrumentation amplifier with dc rejection. This TI Design behaves very similar to any ac coupled circuit in that the dc signal is rejected and the ac signal is passed. The ac transfer characteristic even looks the same as other ac coupled circuits as it has a lower cutoff frequency and a pass band. The main difference is that this circuit does not use large coupling capacitors on the input to ac couple the signal. Rather, the input is dc coupled and the output dc average is eliminated by integrating the output and subtracting the dc average using the reference pin. In section 6.1 we will cover some advantages of this method of ac coupling as compared to the capacitive input coupling method.
Notice in Figure 2 that the integrator (U2) is an inverting integrator. Also, remember that the integral of a sinusoidal wave is zero where as the integral of a dc constant is a ramp function. This circuit will cause the output of U2 to servo to a dc constant voltage that will cancel the output dc offset voltage on this circuit. You can think of the integrator as a low pass filter that translates the instrumentation amplifier into a high pass by canceling the dc and low frequency components on the circuit’s output (see reference 2)
