why this does not work.analysis this

EDAboard.com Forum Index -> Analog Circuit Design -> why this does not work.analysis this

Author

Message

waqas5304

Joined: 09 Sep 2006
Posts: 44
Helped: 1

21 Nov 2006 4:20 why this does not work.analysis this

this is a instruementation amplifier i am trying to use it with single supply as -ve supply is not available in my application.i think it should work but it is not working can anyone tell wats missing in it
why this does not work.analysis this

Sorry, but you need login in to view this attachment

renwl

Joined: 26 Apr 2004
Posts: 455
Helped: 23
Location: shanghai,china

21 Nov 2006 9:51 Re: why this does not work.analysis this

what's the phenomenon?
I have not seen the input bias. you have not draw it in this pic,right?

Google
AdSense
Google Adsense

21 Nov 2006 9:51 Ads

echo47

Joined: 07 Apr 2002
Posts: 4206
Helped: 566

21 Nov 2006 10:05 why this does not work.analysis this

Also, your 600 Hz input seems to be floating. It needs to be constrained somehow so it remains within the common-mode input range of the opamps.

amriths04

Joined: 15 Jul 2006
Posts: 241
Helped: 13

21 Nov 2006 14:54 Re: why this does not work.analysis this

i think you had given the inputs wrong.

amrith.s

timo67

Joined: 21 Sep 2006
Posts: 69
Helped: 3

21 Nov 2006 20:09 why this does not work.analysis this

Hi waqas5304
You dont tell us how doesnt this circuit work, what do you obtain at output?
First of all I hope you know that the output will be around 9V
Your first stage has a gain of (1+2x4.7k/300) ≈ 31
The second stage has a gain of 3.3k/4.7k ≈ 0.7 < 1

My advise for you is :

1 The second stage should have a unity gain with 4 resistors of few 100KΩ
to avoid a relative high current from/to the virtual ground

2 To avoid a non defined common mode range you can bias the inputs each one with two resistances of few 10MΩ.
These resistances should be connected between inputs and 18v power supply and the ground

Any how the output resistance of the input generator must be at least 10 times lower than these bias resistances

good luck

Added after 3 minutes:

verify that the TL074 has enough phase margin to support a total feedback in the follower that provide the virtual ground (9V to real ground)