Re: Question On AGC Design!!
M6-M9 are standard part of OTA amplifier
im3 current is mirrored trough M7 then trough M6 to M8 (im8=im3 if all mosfets are equal, if not you current ratio would be proportional to their ratio)
im4 is mirrored to im9
Your output current is iout=im8-im9=gm1(Vpeak-Vref). This current is integrated trough m12, and lowpassed trough roCo to output.
Since integrator inverts signal you will have output proportional to -(Vpeak-Vref), and you should see how to connect your Nmos in order to have lower resitance(higher nmos Vgs) for higher Vpeak.
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Originally Posted by Anachip
Added after 3 hours 11 minutes:
This is not true!!! There is no Miller compensation if Rf is present!!!
Originally Posted by vgiri
m12 feedback makes that Cf is higher (Miller effect), but in the same time Rf is smaller for the same amount, and your output pole is RfCf.
Precisly: pole at the output of OTA is ro8||ro9||Rf/a *( Cf*a+Cgs12)=RfCf, where ro11,12 are mos outtput resistance (high), and a is m12 voltage gain.
->You can see that there is Miller effect only if Rf/a>>ro8||ro9
1Output pole is w1= 1/RoCo - should be made as dominant
3Non dominant OTA pole is w3=1/Cgs*gm4
To maintain stability w2>betaA0*w1
where betaA is loop gain at small freq...
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