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how to improve the gain of the opamp?

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Aug 18, 2009
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how to improve the gain of the opamp?
i m trying to simulate opamp(specifically for biomedical applications) in Cosmos(synopsys tool) i m not able to get the specified open loop gain 0f 85db
wat to do

Re: opamp

bsudhachandar said:
how to impreove the gain of the opamp?

"improve" ??? Do you mean gain value, bandwidth, linearity, flatness, delay,....???

what do you mean by improve?
can you specify your thoughts so that we can help?


To build a high gain op-amp, start with a telescopic structure, or a folded cascode (if you need the input/output range). They can be found in figure 1 of this paper. Fig 1, b is the telescopic. Fig1 c is the folded cascode.

If the gain is not high enough, you can try to improve the gain by increasing the Length of your transistors. This increases your output impedance which increases then gain.

If thats still not enough, you can use gain-boosting techniques shown in the paper. Here is an example of gain-boosting:
**broken link removed**

Re: opamp

85dB sounds like quite a bit. I think you should either do what eecs4ever tells you, but going for gain boosting techniques, such as regulated cascodes or go for two stages, otherwise you will not get 85dB

thank for ur ideas........
as u sugessted L of transistor can be improved but in my technology file(130nm technology) lmax is specied as 130nm and it is same as lmin value so i think i cant made it high.......
if W of transistor can be made high?
ieee paper i referred hv able to achieve open loop gain of 85-93db.....
does this opamp still need any ckt neeeded to improve gain............

130nm technology limits only the minimum L to 0.13um, of course you can increase your L and W.
The structure the paper presented is a good example. Try to increase the length of M5 ~M12.

Good Luck!

gain-boosting is good method to design high gain opamp.

in my opinion, however, to design opamp which has 85dB gain use gain-boosting method is not appropriate.

maybe you need optimization process for high gain opamp.

the increase of bias current or output impedance to make opamp gain high.

How to optimize process for high gain OP?

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