Differential Amplifier - Op-Amp Circuits
This amplifies the difference between two inputs Vp
and Vn the low impedance
of this configuration is a drawback, but can be used in analog
computing.
Optimum VCC VDD can be +12/-12. AC signals common to Vp and Vn are
canceled by this configuration.
Use a capacitor like 10nF plastic from pin 2 to 3 or across R2 to make
circuit
stable. For AC applications use LF351 TLO71 as they have good slew rate
and
also are FET inputs. For AC applications use a capacitor (1uF) in
series
with Ri to block DC Components. The Inputs have asymmetrical input
impedance
this affects CMRR, also use 1% tolerance MFR resistors for Rf and Ri.

Vout = (Vp - Vn) * (Rf/Ri)
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