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Monday, August 26, 2019

Inverting Amplifier - Op-Amp Circuits

Input Impedance of this module is Ri as pin 2 is at virtual ground, the opamp with feedback tries to maintain pin 2 and 3 at same potential pin 3 is at 0V hence pin 2 is at virtual ground. Clamping diodes protect OpAmp, Rf + Ri is between 5kE and 1ME as an opamp may be able to drive around say 5mA max.

Inverting Opamp - Interactive Simulation

Current into node pin 2 = Vin/Ri if Vin is +ve it raises potential at pin 2, in order to bring it to 0V the OpAmp sucks away the current by turning its output negative the current leaving pin 2 node is also Vin/Ri. Then Vout is given by Vin/Ri * Rf as per V=IR ohms law. Most OpAmps output swings around 1v less than VCC/VDD for full swing use CA3130 this is a FET input OpAmp, and has low bias currents in pico amps.
Inverting Amplifier - Op-Amp Circuits

Vout = Vin * (-1) * (Rf/Ri)

This is used as a small signal amplifier. Used after the buffer stage. Multiple stages cascaded for higher gains. An Interactive Tutorial with Simulated Meters and Potentiometers, demonstrating how an Inverting Operational Amplifier functions in page below.

More at Analog Op-Amp Circuits