In the Op-amp circuit application example "Quick Fundas: Op-amp# 6" we have seen that the output of the Op-amp circuit oscillates between positive and negative saturation voltages when VIN is set to 0V. How the output voltage behave when the input voltage VIN is set (-2V) and when VIN is set (+2V)?
Ans:
Setting VIN (-2V) helps in the capacitor C2 to be charged to the negative threshold voltage faster. At the same time it takes more time for the capacitor C2 to be charged to the positive threshold. Hence the Op-amp output VOUT remains in positive saturation for more time than the time it remains in negative saturation.
The opposite happens when VIN is set at (+2V). In that case, the Op-amp output VOUT remains in negative saturation for more time than the time it remains in positive saturation.
Basically this is kind of a PWM (Pulse Width Modulation) circuit using an Op-amp. Pulse width modulation is achieved by varying VIN. In the picture below, the simulated waveform of the output VOUT is shown when VIN is varied from (-2V) to (+2V).
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| Figure 1: Pulse Width Modulation waveform (for circuit shown in Op-amp# 6) |
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