Misread CB Amplifier

@May/31 2016

 Input impendance

answer is NO,  R6 almost does not impact the input impendance. 

several way to understanding this:

1. R6 reflect to emit as R6/β

2. C3, actually not provide signal to ground path, the input impendance only related to current different between in Ic/Ie.

3. C3 is provide some DC bias , look like.

4. input is R1//R6//R9//R2?? noway, disconnect R6, C3(don't connect to GND), R2,R9 8.2k,3.2k, input 354 ohm,  82, 32, also around 

354 ohm . they are not parallel to form input impendance !!!!!

5. even remove C3, R6, the input impendance still very low, and gain could keep to 1 mhz, reset my brain!!!

6. the CB config, the emit been bias to a DC voltage and became a "voltage source", this understanding explain much much misery phenomenon happened hear..

Understanding the CB simulation result

base current is inverses polarity with base voltage.

base to gnd capacity：

ac current path, base voltage change very very little. almost flat, so change the Vbe change the current...