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Design >> Analog Design >> MFB high-pass Filter not having a unity gain
https://designers-guide.org/forum/YaBB.pl?num=1330191691

Message started by gido on Feb 25^th, 2012, 9:41am

Title: MFB high-pass Filter not having a unity gain
Post by gido on Feb 25^th, 2012, 9:41am

hello,
I am designing a high-pass filter using the multiple feedback configuration. I am doing the AC analysis and i have tried several times but it is not giving me a unity gain (1000mV). my input voltage is 1V.
I have changed op-Amp design but still no nice result.
Can anyone help me here?

I am running cadence.

Thanks

Title: Re: MFB high-pass Filter not having a unity gain
Post by rfidea on Feb 25^th, 2012, 10:21am

The gain of a MFB filter is set by a resistor ratio. Please look at page 7 in the following document.

http://www.ti.com/lit/an/sloa049b/sloa049b.pdf

As a general recommendation I think you should start the filter design with an ideal opamp, use an inverting amplifier with a lot of gain. Then you will see if you have a fundamental problem with your RC networks or not. Get that to work first. It it then do not work with a real opamp, the problem is related to the opamp.

Title: Re: MFB high-pass Filter not having a unity gain
Post by buddypoor on Feb 26^th, 2012, 9:44am

gido wrote on Feb 25^th, 2012, 9:41am:

I suppose it shouldn't be a problem to give you some hints - but without any circuit information? What do you expect?