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Subject: Telescopic cascode

Date: 08/11/03 at 7:37 PM
Posted by: Jason
E-mail: jason_class[AT55]yahoo.com (replace [AT55] with @ to reply)
Message Posted:

Hi Everyone,

Good Morning!
I would like to ask for help on telescopic cascode. I really wish anyone who can help to englighthen me.
I have uploaded a page on the following site;

http://www.geocities.com/toowang/telescopic.gif

During the lecture, the lecturer said that Q1 and Q2 must not be operating in triode region. He said that Vb1 and Q3 made it possible. I do not get his point. Can you help me to understand this? Also, is it true that for all mosfet component in an amplifier, they are all perform in saturation region in order to supply constant Id?

The lecturer mentioned about 'dominant point/pole' between Q7 and Q8. This term is new to me. May I know what is it? How do we determine where a 'dominant point/pole' is?

The lecturer mentioned about the path from Q8->Q3->Q1->current source->ground using the following equation,

Vcc-|Vgs|-Veff-Vin-Vgs1>=Veff1 ----eq1.1

Vcc-|Vgs|-Veff-Va>=Veff1 ----eq1.2

In equation 1.1, I do not know why we need to minus Vin at Q1. Why at Q3, we do not need to minus Vb1 instead?
In equation 1.2, why dont we minus any voltage drop or Vin in the equation?

Why do we need to get a equation involving Veff1(for Q1)? Any help in analysing the circuit?

Kindly enlighthen me and roughly let me know the reason for using each component in this circuit.

I am struggling hard on this. Kindly help me, Experts.
Thank you and have a good day ahead

Thanks a lot

best regards and thanks
Jason


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