Question

Design an adder circuit using op-amp to satisfy following equation:

- Vo = V1 + 3 V2 + 2 V3 + 2V4 + 4V5 The supply voltage of the op-amp is +- 13V and output saturation voltage is +- 12 V. The circuit should always operate in its linear range. What are the minimum-maximum voltage values of V1, V2, V3, V4 and V5 when only one of them is connected to the input at a given time (i.e. other input voltages are zero)? What is the value of maximum voltage Vi if V1 = V2 = V3 = V4 = V5 = Vi ?)

Answer 1

1. The adder design is shown on the picture.

2. In order for circuit to operate in its linear range, the minimum-maximum voltage values of V1, V2, V3, V4 and V5 when only one of them is connected to the input at a given time should be the following:

V1 = -12..12V; V2 = -4..4V; V3 = -6..6V; V4 = -6..6V; V5 = -3..3V.

This can be found by noting the fact, that each voltage is multiplied by the some coefficient, so the result output voltage should not exceed 12V.

3. If V1 = V2 = V3 = V4 = V5 = Vi, the output voltage will be: Vo = -Vi(1+3+2+2+4)=-12Vi. As far as it is nessesary to be |Vo| less then 12, the input voltage should be in range Vi = -1..1V.

Answer. 1) See picture.

2) V1 = -12..12V; V2 = -4..4V; V3 = -6..6V; V4 = -6..6V; V5 = -3..3V.

3) Vi = -1..1V.