about folded cascode amplifier

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Hafedh

Joined: 15 Feb 2008
Posts: 112
Helped: 46
Location: Sfax, Tunisia

11 Aug 2008 8:52 about folded cascode amplifier

hi
I'am studying the structure of fully differential folded cascode amplifier with cmfb.

the simulatin result of the gain and the phase are as following :

although the cutting frequency is 2.4MHz.
so, why the curve of the gain drop rapidly from 62db, normally it should remains constant until it reaches the cutting frequency.

thanks for your help...

*if you have any documents about this structure thanks to send it to my personal e-mail : fendri.hafedh(at)hotmail.com

ricklin

Joined: 20 Feb 2006
Posts: 79
Helped: 9

11 Aug 2008 15:23 about folded cascode amplifier

Usually for AC analysis, You need to scale your X-axis with log scale instead of a linear scale, then you'll see the curve as you described. Folded cascode will have high output resistance, so the dominant pole will be at very low frequency as several kHz, and your scale is Meg Hz/div, then the low frequency response stucked together, and you can hardly tell the 20dB/DEC rolling down.