TIDUEU6B September 2020 – December 2021 OPA810
In this method of measurement, the inverting node of A2 is not measured. The assumption behind this method is that the inverting node of A2 is 0V since it is equal to the non-inverting node. This case is only possible in the ideal scenario where the Aol of A2 is infinity. But due to the finite open loop gain of op amp there will always be some small voltage at the inverting node of A2. This voltage is inversely proportional to Aol. As practical op amps have gain decay with respect to frequency, Aol will decrease significantly as the frequency increases. It makes this method of measurement erroneous at high frequencies. Hence the Aol of the amplifier plays a very crucial role in this method of measurement and should be as high as possible. Figure 2-9 explains this method of measurement.
As this method measures both voltages with respect to ground, data can be acquired using a single-ended ADC.