The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> finding number of zeros in emiter follower
https://designers-guide.org/forum/YaBB.pl?num=1350801719

Message started by aman gupta on Oct 20^th, 2012, 11:41pm

Title: finding number of zeros in emiter follower
Post by aman gupta on Oct 20^th, 2012, 11:41pm

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
PLEASE HELP

Title: Re: finding number of zeros in emiter follower
Post by raja.cedt on Oct 22^nd, 2012, 2:31am

hello,
refer the following pap

http://www.ece.ucsb.edu/Faculty/rodwell/Classes/mixed_signal/Hajimiri_MOTC.pdf
Basically to find the number of zero's you have to find how many infinite value capacitor's will give non zero output.

Thanks,
Raj.

Title: Re: finding number of zeros in emiter follower
Post by summi on Oct 23^rd, 2012, 3:52pm

Dear raj,
recently i have started learning analog, i am so keen to learn how to calculate zero without doing math. Unfortunately i haven't understand that pap. Could you please tell me what is infinite value capacitor and i will be more happy if you can give me some simpler doc.

Br,
Summi.

Title: Re: finding number of zeros in emiter follower
Post by raja.cedt on Oct 24^th, 2012, 4:22am

hello,
true. Finding zero's bit tough,unless you are very familiar with the method what he gave in the pap. He confuse little bit by suing many variables and different terminology. Take a circuit and find total number of capacitors. Let us say 3 so there can be max three zero's. Now short all capacitors and check the output (interested variable it could be voltage or capacitor), if it non zero then 3 zero's. if not short two leave one cap open and check if you have non zero output and repeat the experiment with all other capacitors. Out of 3 trails if you get non zero out put at any time, that indicate 2 zero's. If not short one and open 2 capacitors......

believe me i don't prefer this method to find zero's, however the method open circuit time constant to find poles is much simpler.

Try to read the following.
http://www.ece.ucsb.edu/Faculty/rodwell/Classes/mixed_signal/Cochrun_Grabel_MOTC.pdf

Thanks,
Raj.

Title: Re: finding number of zeros in emiter follower
Post by buddypoor on Oct 25^th, 2012, 2:37am

I think, for the shown example circuit finding number of zeros is a simple task:

Find the number of capacitors which cause a highpass characteristic.

Title: Re: finding number of zeros in emiter follower
Post by summi on Oct 27^th, 2012, 11:55pm

dear buddypoor,

CC1 will create a zero due to it's high pass nature, but how abut rest of the capacitors, I have derived but want to know is there any directly method to find?

Br,
Summi