LNA设计疑问，请高手解答！谢谢

brwn

看到一些LNA设计方法，有几个问题想请教各位。
1、初期选管子的时候如何判定管子的稳定性？K值如何的来的？？K值是如何定义的？
2、再阻抗匹配的时候，如何在圆图上找到等噪声系数圆和等增益系数圆？
先谢谢各位了！

vlivli

K值通过S参数计算出来的，用S参数仿真选择等噪声系数圆和等增益系数圆。

wangmou333

建议找几本微波放大器方面的书先来看看，不要急于求成。

kinpoagilent

The classical parameter for determining stability has been Rollett? [1] K factor. The K factor is necessary but not sufficient by itself to determine stability. An additional term, typically the stability measure, B1, is required to be used in conjunction with K. These two factors are both derived from S-parameters with the requirement for unconditional stability of:


K > 1 and B1 > 0

kinpoagilent

K  (dimensionless) ?Rollett? Stability Factor. A circuit is unconditionally stable if both K > 1 and B1 > 0. If |S12| = 0, the circuit is unilateral and K is infinite.

Values of K that are > 1 are highlighted in a contrasting color in the Tabular List display as a means of quickly identifying frequencies at which the device is potentially unstable.  A horizontal K = 1 line is also plotted in the Rectangular Plot for quick reference.

At frequencies for which K is infinite, K is plotted with an arbitrary value of 20 and a message to that effect is displayed in the plot area. Infinite values of K are shown as ?nfinite?in the Tabular List.

Values of K > 1E6 (but less than infinity) are displayed as " > 1E6" in the Tabular List. Extreme values of K less than infinity are plotted without restriction. Note that some plots may show both infinite K as well as values of K that are extremely large.