Page 391 - Op Amps Design, Applications, and Troubleshooting
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Subtracter 367
According to the Superposition Theorem, the output should be the net result
of the two individual input signals. That is, the output voltage will be +V A ~ V B.
Thus, we can see that the circuit does indeed perform the function of a subtracter
circuit,
9,2.2 Numerical Analysis
The numerical analysis of the subtracter circuit is straightforward and consists of
applying the Superposition Theorem. Let us first assume that the V A input is
grounded and compute the effects of the V B input. The output will be equal to V B
times the voltage gain of the inverting amplifier circuit, which is
Now let us ground the V B input and compute the output voltage caused by the
V A input. First, V A is reduced by the voltage divider action of R 3 and K 4. The volt-
age appearing on the (+) input is computed with the basic voltage divider equa-
tion.
The voltage on the (+) input will now be amplified by the voltage gain of the non-
inverting op amp configuration, which is
The actual output voltage will be the algebraic sum of the two partial outputs
computed:
