本帖最后由 xljin2011 于 2013-9-12 13:34 编辑
先说明一下，此贴还未结！
Razavi书中3.2小节最后引出了一个关于放大器放大倍数的辅助定理。为说明方便，我先把相关原文抄一下：
Lemma. In a linear circuit, the voltage gain is equal to -GmRout, where Gm denotes the transconductance of the circuit when the output is shorted to ground and Rout represents the output resistance of the circuit when the input voltage is set to zero[Fig. 3.25(a)].
The lemma can be proved with the aid of Fig. 3.25 by noting that the output port of a linear circuit can be modeled by a Norton equivalent.That is, the output voltage is equal to -Iout Rout, and Iout can be obtained by measuring the short-circuit current at the output. Defining Gm=Iout/Vin, we have Vout = - Gm Vin Rout. This lemma prove useful if Gm and Rout can be determined by inspection.
首先，书上说，“Gm denotes the transconductance of the circuit when the output is shorted to ground”,意思应该是the output is shorted to a fixed voltage. And”Rout represents the output resistance of the circuit when the input voltage is set to zero”, should be”the input is set to a fixed voltage.”。 可能是表达的不太确切。这是小问题。
其次，书上说“the output voltage is equal to Iout Rout”, 在图（a）中，Rout上是没有电流的，(因为Rout两端短接)，而在图（b）中，Rout上的电流是由Vout决定的，那么此处的Iout又是指什么呢？书上说，“Iout can be obtained by measuring the short-circuit current at the output”,意思Iout 等于图（a）的输出短路电流，那么当然有Gm=Iout/Vin.，Vout = - Gm Vin Rout, 问题是”the output voltage is equal to Iout Rout”中的Iout 为什么等于输出短路电流呢?
一点小小的疑惑，烦请各位帮忙.
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