Q4Analog Electronics

Question

(B) For fig. 5 find output voltage of the op-amp. Given R1 = 5 K\Omega, R2 = 10 K\Omega, R3 = 5 K\Omega, R4 = 5 K\Omega for Fig. (7).

Answer 1

A difference amplifier (subtractor) using an Op-Amp with $R_{1} = 5 k Ω$ , $R_{2} = 10 k Ω$ , $R_{3} = 5 k Ω$ , $R_{4} = 5 k Ω$ (but using Fig. 7 notation where all = 5kÎ©, Rf = 10kÎ©). The general output voltage expression is:

V_{o u t} = \frac{R _{2}}{R _{1}} (V_{2} - V_{1}) when \frac{R _{3}}{R _{4}} = \frac{R _{1}}{R _{2}}

Given $R_{1} = 5 k$ , $R_{2} = 10 k$ , $R_{3} = 5 k$ , $R_{4} = 5 k$ :

A_{d i f f} = \frac{R _{2}}{R _{1}} = \frac{10 k}{5 k} = 2

Therefore: $V_{o u t} = 2 (V_{2} - V_{1})$ . For $V_{1} = 1 V$ and $V_{2} = 2 V$ (example), $V_{o u t} = 2 (2 - 1) = 2 V$ . The circuit amplifies the differential signal by a factor of 2 while rejecting any common-mode signal.

Q4Analog Electronics

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