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Recommend me a structure for a buffer with a fixed gain

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abcyin

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Hi, all

I want to design a buffer at the last stage of an amplifier to drive a lower resistor, and it is proposed to have a fixed gain, 10dB for example, which structure will you recommand for me,

Thx in advance!

BR!
 

aryajur

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Re: Buffer question

It depends on what kind of an output swing you are looking for. You can use a Common Source if you want higher swings or a class AB stage. Or if swing is not important a Source follower may be a good choice.
 

    abcyin

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abcyin

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Buffer question

Thx for your reply.
Yes, I care about the output swing of the stage, because it is the last stage of the receiver, so the linearity is very important.
And as to the source follower, I think it will cost a lot of current to achieve a wide bandwidth and a good linearity, and also it is hard to get a fixed gain by the source follower,
so maybe you can give me a detailed explanation about the common source or class AB structure, or if you can share some literature on that, I will be appeciate it,
thx very much.
 

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Re: Buffer question

Razavi has a nice section on Linearity where he basically gives you the tools to analyse non linearity of any circuit, so you can analyse different stages to decide among them on the basis of linearity. The fixed gain part is what seems a little flaky to me, it would be too tought to have a exact gain especially on chip. To aim for this you need to create your feedback using some kind of feedback since that would help your linearity and stabilize the gain also, for example source/emitter degenration.
 

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