Low-frequency RC-Amplifier Combination
Now and then, we try to feed you a real-world problem. This is one of those times. A
signal generator in the fluorescence photobleaching recovery apparatus drives an
amplifier which, in turn, drives an electromechanical device to effect the modulation of
the signal (it’s a long story). Anyway, input to the amplifier is a perfect triangle wave at
16Hz. The output of the amplifier is a lumpy triangle wave—pretty ugly. The problem is
the output impedance of the amplifier, which can be modeled as a capacitor.
a. If the impedance of the electromechanical device is assumed to be purely resistive at 8
ohms, what size capacitor must you choose to have good frequency response at 16Hz?
b. Man, that’s a big capacitor! And capacitors do block DC current. Why would I want
a BIG blocker of DC current if, afterall, what I really want is a lot of signal at a low
frequency not that far away from DC???