Calculating 3db freq. using open-circuit time constant method

Thread Starter

Steve|

Joined Nov 4, 2008
17
Hi, this is the original circuit:



They ask me to calculate the corner frequency using the open-circuit time-constant method assuming ro->infinity and rb =0. The previous question asked to draw the small signal equivalent circuit for high frequency AC analysis. So I assumed from this circuit, I could reduce it into a simpler form:


I don't understand why R1 has disappeared...

Thanks.
 

Thread Starter

Steve|

Joined Nov 4, 2008
17
Ah nm I think i figured it out, since R1 is parallel to Rb and they're both grounded, with rb=0, you can ignore r1. That's just my guess.. =\
 
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