# Interview questions on Analog Signal Processing

What is the voltage across each element and what is the voltage v in each case?

For the last circuit, are there element values that make the voltage v equal zero? If so, what element values work?

Again, for the last circuit, if zero voltage where possible, what circuit element could substitute for the capacitor-inductor series combination that would yield the same voltage?

This circuit served as a transducer, converting light energy into a voltage vout. The photodiode acts as a current source, producing a current proportional to the light intesity falling upon it. As is often the case in this crucial stage, the signals are small and noise can be a problem. Thus, the op-amp stage serves to boost the signal and to filter out-of-band noise.

Find the transfer function relating light intensity to vout.

What should the circuit realizing the feedback impedance Zf be so that the transducer acts as a 5 kHz lowpass filter?

A clever engineer suggests an alternative circuit to accomplish the same task. Determine whether the idea works or not. If it does, find the impedance Zin that accomplishes the lowpass filtering task. If not, show why it does not work.

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