finding number of zeros in emiter follower

Discussion in 'General Electronics Chat' started by amangupta1219, Oct 21, 2012.

  1. amangupta1219

    Thread Starter New Member

    Oct 18, 2012
    how can i find the number of zeros in a circuit ?
    i am attaching a circuit of emitter follower in which i want to find the high frequency response. Instead of deriving the whole transfer function , i am using OPEN CIRCUIT time constant method to find the poles and midband gain formula by neglecting the effects of capacitors.
    Now i know that the number of poles will be equal to 2 because there are 2 independent capacitors.
    But i am not able to find the number of zeros. Neglect the load capacitor CL
    Last edited: Oct 21, 2012
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    I am not familiar with the OPEN CIRCUIT time constant method (at least, not by that name).
    You apparently are accounting for the leading (high pass) poles due to the series capacitors.
    A series capacitor with no shunt resistance or inductance also always results in a zero at the origin.
    Also, I'm pretty sure Cπ results in a zero and a pole. In the real world, they may be swamped by the Ft of the transistor, which is another lagging pole.
    There are also at least two more lagging (low pass) poles. Have you accounted for those?