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  1. #1
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    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. Click image for larger version. 

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ID:	156126 Click image for larger version. 

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

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



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  3. #3
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    Re: Difference between two biquads shown in diagram

    Quote Originally Posted by FvM View Post
    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.
    Click image for larger version. 

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  4. #4
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    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.



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