Nonlinear Overshoot in 0.18um CMOS Op-Amp

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matchasm

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Hi,

I am designing an Op-Amp with around 200MHZ GBW and 100-dB DC gain and I notice that when I reduce the noise by width-scaling I get some overshoot in the transient response. The AC phase margin is alright, so anybody got any other suggestions?
 

Not enough details. Post schematics and transient response graph, then chances to get help would be higher.
 

My BLIND guess is that your phase margin shrinks due to the width-scaling. Check it.
 

I would rather say that scaling could be sucessfully used only in digital circuits. In the case of analog electronics simple scaling is not enough because of sub treshold effects.
 

steer said:
Not enough details. Post schematics and transient response graph, then chances to get help would be higher.
Click to expand...

Alright. Here's a rough schematic and transient response. The amp is used in a switched-cap MDAC configuration.
 

how about the phase margin? did you add all load when you simulate the phase margin?
 

pfd001 said:
how about the phase margin? did you add all load when you simulate the phase margin?
Click to expand...

yep, and switches are in the right position too. i can change the compensation network to adjust the phase margin any way i want, but the overshoot always remains.
 

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