This “unusual zoom amplifier circuit” allows you to “zero out” a DC voltage and then amplify a small AC signal which is superimposed on the much larger DC level. When switch SW1 is closed, both INA128 inputs see the same AC + DC level and its high common- mode rejection results in zero volts output. When SW1 is opened, the DC level is stored on C1 but now the AC signal is applied to only the inverting input where it is amplified by a factor of 1000x. The droop rate of C1 depends on the leakage of SW1 and the input bias current of U1.Using a glass reed relay and an INA116 (Ib = 5fA typ), extremely low droop rate can be achieved. A high insulation resistance dielectric capacitor is necessary– teflon, polystyrene, etc. (Circuit is created by Neil P. Albaugh TI- Tucson)
Zoom amplifier circuit:
Online Simulation of a Zoom Amplifier Circuit
The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.
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