# Difference between two biquads shown in diagram

1. ## Difference between two biquads shown in diagram

Hi

I have two different biquad circuits. Fisrt biquad shown in the attached figure is a fully differential biaquad with four gm blocks while the second figure shows a single ended biquad with two gm blocks. I want to know why in the first circuit four gm blocks are used while in second circuit two gm blocks are used. A biquad can be designed using two gm blocks and two capacitors what is the reason of using four gm blocks in first ciruit? The difference is not the fully differential or single ended version.    Reply With Quote

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2. ## Re: Difference between two biquads shown in diagram

Both circuits implement different transfer functions. Why don't you calculate it?  Reply With Quote

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3. ## Re: Difference between two biquads shown in diagram Originally Posted by FvM Both circuits implement different transfer functions. Why don't you calculate it?
Thankyou for your reply. I have derived. Both are having same Transfer functions if all gms are same. Please see the attached. If same than what is the advantage of using four Gm blocks instead of two Gm BLOCK. 1 members found this post helpful.  Reply With Quote

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4. ## Re: Difference between two biquads shown in diagram

You are right, I overlooked one short in the first circuit.

The answer is, fully differential is only possible in the four block topology.  Reply With Quote

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