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Design >> RF Design >> about the ratio between bias circuit and main LNA circuit
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Message started by yixiusky on Mar 2^nd, 2010, 9:25pm

Title: about the ratio between bias circuit and main LNA circuit
Post by yixiusky on Mar 2^nd, 2010, 9:25pm

Hello everyone:

I would like to ask one question about the ratio between bias circuit and main circuit.

I design the LNA.

The bias reference current is 100uA, the main circuit current is 10mA.

There are two choice to decide the ratio (1) 1:100 (2) 1:10: ~ 10:100 use two branch

(a) Which one is better considering about mismatch,...?

(b) And except simple current mirror, is there any method or reference talk about high ratio (1:100) current mirror?

Thank you very much

Title: Re: about the ratio between bias circuit and main LNA circuit
Post by rfmagic on Mar 4^th, 2010, 12:16am

Hi yixiusky,

In order to reduce mismatch you better use multiplicity of no more than 10. Further more, I use the last transistor of the current mirror (the one that's mirroring the LNA core) as RF transistor with same width and length as the LNA CS transistor ( but different multiplicity). this way you can ensure that the current mirror will follow the LNA CS transistor over PVT variations.

Kob

Title: Re: about the ratio between bias circuit and main LNA circuit
Post by yixiusky on Mar 4^th, 2010, 1:54am

Hi Kob

thank you very much , you helped me ^^