[MEC] 共源極放大器加源極電阻小訊號分析整理 DC and AC Analysis of Common Source Stage with Source Degeneration

（允許非商業用途再利用的MediaTek晶片照片）

接著繼續拿CS的變異版—CS with Degeneration來練練畫圖。
有需要的觀眾歡迎下載使用。

其實這次的電路和上一篇的電路非常相似，
就只差在Source少了一顆旁路電容，
這樣一來交流分析的時候，
Source端就會多出來一顆電阻R。

那這顆電阻會造成什麼樣的影響呢？
就來看看放大器的三項關鍵參數有甚麼變化吧！
(1)輸入阻抗Rin維持不變
(2)輸出阻抗Rout增大
(3)電壓增益Gain變小（但因為增益有負號在，實際上是變大，變得更靠近零。）

(4)頻率響應的部分還沒有複習到就先不列出來

以下幫大家整理等效μ電路。

It is difficult to derive the gain of a common source stage with a source degeneration resistor, even the textbook written by Sedra Smith skipped the discussion.


Luckily, the textbook “Design of Analog CMOS Integrated Circuits” written by Behzad Razavi showed us how to derive the gain. It is printed on page 66 of the first edition as equation (3.71). The method Prof. Razavi used is nodal analysis. Here we are going to seek the answer in a different approach.

至於如何得到輸出阻抗，
咱們就等到明年再揭曉答案，
2017年再十分鐘就要結束啦！

If you are curious about how to derive the output impedance, read my next post. See you in 2018.