I have to design a circuit that will undo the effects on a signal passed through a "black box". I have already determined that I have a pole at 500rad/s and a zero at 2000rad/s and a max phase shift of ~ -37* at ~950rad/s. It has a DC gain of 1 and a HF gain of ~0.25. The input signal is a sine wave of between 0 and 20k Hz. I have attached the gain and phase diagrams. We can only use 1mH inductors and 741 op amps but a range of resistors and caps are available.(adsbygoogle = window.adsbygoogle || []).push({});

I have designed a circuit (between the buffer amp to prevent loading and the inverting amp gain -1 to send it positive again) just using a simple inverting op amp circuit and a series combination of L and R for each the Zf and Zi that will undo this (same R, L in Zf 4* L in Zi), but the problem is that I thought I had much larger inductors (100mH) to work with. Doing it this way the ratio of R to L is only 2000:1, which gives values of R about 10 Ohms, less that the output impedence of the 741.

There has to be an easier way that is just eluding me! I have tried working out transfer functions for all manner of simple amps using just L and R values in the impedences that determine gain, but I'm comming to a dead end. Perhaps I need to use a voltage divider before the input to the amp? I've tried some of those too but still to no avail.

Help me please!

I've just found out that we can use capacitors and edited the post, now on to try again!

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# Homework Help: Pre emphasis circuit design

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