Wednesday, March 2, 2011
Null Loop Gain Question
For question 1 of HW6 I have expressions for G0, Ginf, and T. I'm now chasing Tn. It's tempting to just use reciprocity to find it but the next step is to check the reciprocity relationship so that would be somewhat redundant. Starting with iy/ix with vout = 0, it appears that ix would be zero since vout = 0 (This is with the test source between gm and R0 and ix is the current between gm and R0). That being the case, Tn will either blow up or be zero depending on the value of iy. Obviously I'm missing something here. Any hints on how to find Tn?
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No responses. I guess I'll respond to my own post. Here's what I'm thinking. By nulling the output we put R0 in parallel with (R3+1/sC1) which is in parallel with R2. From there it's just a voltage divider with R1. If anyone has a moment please let me know if I'm off base or not.
ReplyDeleteWrich,
ReplyDeleteThe output is zero by superposition of the iz & vin sources.
If you set vout to zero, you should be able to see what ix is by inspection. The problem does not ask for R0 of the gm amplifier to be included.
You should also easily see what vm is, and hence iy.
I hope that helps.
Just note that v^out in this case is v^c (i.e., Tn = i^y/i^x when v^c=0 (vout is the opamp output, not the converter output). Hence, i^x will be the current flowing in the feedback path formed by R3-C1 (because Ro = infinity). Hence, determine i^x in terms of v^c and v^m. Express i^y in terms of gm and v^m. Now you have everything to determine Tn.
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