Question

Design an op-amp circuit for a weighted summer that shifts the dc level of the input signal vi(t) = 3 sin(t) V from zero to -3 V. Assume that in addition to vi(t), you have a dc voltage source of 1.5 V available. Sketch the output signal waveform.

Answer 1

The equation of summing amplifier can be write as,

Vout = Gain₁ x Vin_sin + Gain₂ x Vdc_1_5

Here, Vin_sin = 3sin(t) volt and Vdc_1_5 = 1.5 volt

Now, Gain₁ = 1 and Gain₂ = 2

Design with above can be done by,

R₁ = Feedback resistor = 2 k ohm

R₂ = Series resistor for 1.5 volt DC input = 1 k ohm

R₃ = Series resistor for 3 volt AC input = 2 k ohm

So, Gain₁ = R₁/R₃ = 1 and Gain₂ = R₁/ R₂ = 2

Designed Weighted Summing Amplifier is shown below,

Input Signal Waveform,

Output Waveform,