微波EDA网,见证研发工程师的成长!
首页 > 研发问答 > 微波和射频技术 > 天线设计和射频技术 > Can I determine what Q point is used by examining bias resistors and voltage? (FET)

Can I determine what Q point is used by examining bias resistors and voltage? (FET)

时间:04-06 整理:3721RD 点击:
For example, we repairing some FET-based oscillator.
Biasing resistors used: 30 Ohm on drain and 400 Ohm on source. Supply voltage is 2v, so i guess that I=2v/430Ohm=0.0046=0.5mA
Then i measure Vgs, for example it is -1v. Then I=1/400=0.0025A. So the Q point is -1V / 0.0025A, and DC load up to 0.5mA... I know the numbers are wrong, but how about idea?

Yes, it's a guess - but wrong. But where comes this guess from? Do you know the working principle of a FET?

Backwards from choosing bias resistors. I try to figure it out... What i should measure, for example in lna fet, to get its q? In terms of u,i,r...

The FET must be regarded as a voltage controlled current source - controlled by VGS. The voltage VGS is determined by the gate potential and the source potential (voltage drop across RS).
The control function can be derived from the FET theory.

Copyright © 2017-2020 微波EDA网 版权所有

网站地图

Top