The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Amplifier 2nd second stage topology clarification
https://designers-guide.org/forum/YaBB.pl?num=1593332645

Message started by Chetan Kulkarni on Jun 28th, 2020, 1:24am

Title: Amplifier 2nd second stage topology clarification
Post by Chetan Kulkarni on 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

Title: Re: Amplifier 2nd second stage topology clarification
Post by Tako on Jul 2nd, 2020, 4:38am

Hi,

Where exactly you would like to put another opamp?

Title: Re: Amplifier 2nd second stage topology clarification
Post by Chetan Kulkarni on 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)

The Designer's Guide Community Forum » Powered by YaBB 2.2.2!
YaBB © 2000-2008. All Rights Reserved.