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Design >> Analog Design >> Differential Difference Amplifier
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Message started by aaron_do on Oct 25^th, 2013, 2:09am

Title: Differential Difference Amplifier
Post by aaron_do on Oct 25^th, 2013, 2:09am

Hi all,

I'm looking to design a closed loop differential-in, single-ended out unity gain amplifier. It needs to have very good CMRR. One way to design such a circuit is to use an instrumentation amplifier. However, an instrumentation amplifier drives resistive loads in the first stage, making it a little power hungry. I found such a circuit can also be designed using a differential difference amplifier with feedback.

Does anybody have any experience with this circuit? How does it compare to a normal op-amp in unity-gain feedback in terms of accuracy. Alternatively, does anybody know of other good options?

Any feedback is appreciated.

thanks,
Aaron

Title: Re: Differential Difference Amplifier
Post by wave on Oct 25^th, 2013, 10:47am

Sure, I've designed one with a cascoded current mirror. Just tack on another Diff pair. Mine was fully diff'l so I spend a lot of time on CMFB amps. You should get similar specs to any similar amp of the same technology. Make sure the CM of input 1 is similar to CM of input 2.

Ref: Sackinger

Good luck,
Wave :D

Title: Re: Differential Difference Amplifier
Post by aaron_do on Oct 27^th, 2013, 7:55am

Thanks for the reply.

Yeah I've read that paper. Its interesting. I've just got this feeling that I'm not going to get the same kind of performance as a typical opamp in feedback. I guess I need to do some analysis.

thanks,
Aaron

Title: Re: Differential Difference Amplifier
Post by shaikss_rf on Nov 26^th, 2013, 3:39am

aaron_do wrote on Oct 27^th, 2013, 7:55am:

For one of my designs, I need to design a Instrumentation amplifier using DDA approach. Can you pls throw some light on this?

Title: Re: Differential Difference Amplifier
Post by aaron_do on Nov 27^th, 2013, 12:25am

Hi,

do you have any specific questions? I referred to a paper in ieeexplore. Just search for Differential Difference Amplifier...

Aaron

Title: Re: Differential Difference Amplifier
Post by shaikss_rf on Nov 29^th, 2013, 2:14am

Hi,

I, too, referred an IEEE paper. I am designing an Instrumentation amplifier using DDA approach. I tried to optimize the circuit to get desired results but phase margin is very bad. I have attached the circuit and plot.

Title: Re: Differential Difference Amplifier
Post by aaron_do on Nov 29^th, 2013, 2:24am

Hi shaikss_rf,

I suggest you attach the images directly to the post, instead of using a zip file.

Aaron