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Aug 4th, 2020, 9:56am
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Amplifier 2nd second stage topology clarification (Read 196 times)
Chetan Kulkarni
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Amplifier 2nd second stage topology clarification
Jun 28th, 2020, 1:24am
 
Hi all,

I am designing a front end for capacitive sensing application and mixer for lock-in demodulation. The mixer is double balanced voltage mode passive mixer (50% duty cycle) and LPF filter is differential RC filter for cut off frequency of 1KHz. Please find the attached image(system.png)

One of the mixer input is connected to amplifier output and the other input of the mixer is connected to reference voltage. The mixer's differential output is connected to differential RC LPF. The equivalent circuit (not sure though) can be seen from image (equivalent_load.png).

I am at stage of decide the second stage topology for my front end amplifier. As it is not typical capacitive load, I am not sure about what topology fits my application.

Amplifier specification:(preliminary)
GBW ~ 400Mhz (based on Noise gain)
F3db = 20MHz (closed loop)
Noise gain ~ 15 (Cf = 60f , differential sensor cap = 700f )
Acl = 0.5
Aol = 65dB

Can someone please guide how to analyse the load for the amplifier and topology for second stage?

Thanks in advance

Regards,
Chetan
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Tako
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Re: Amplifier 2nd second stage topology clarification
Reply #1 - Jul 2nd, 2020, 4:38am
 
Hi,

Where exactly you would like to put another opamp?
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Chetan Kulkarni
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Re: Amplifier 2nd second stage topology clarification
Reply #2 - Jul 7th, 2020, 4:33am
 
I wanted to decide on the second stage of 1st amplifier ...(meaning Class AB output stage or Class A stage)
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