Differential Amplifier

[mobile-it]

Hi all,

Can someone explain me why by the differential amplifier configurations by the differential output configuration there is need for 2 Rc and when using single-ended output you have only one Rc!


Thanks in advance!

 

[seadolphine2000]

The idea of differential amplifier is that you have 2 identical branches. (Transistors, resistors,..) should be the same so as to make the differential gain twice the single-ended gain.

For more info, refer to
"Microelectronics"
Adel S. Sedra & Keneth C. Smith

 

[mobile-it]

Hi,

Yes you are right but: the single ended output differential amplifier hasn't got 2 identical parts; it has one side with a resistor in the collector and one without it... why is this? I can't find an answer in this book... also not in Malvino - Electronic Principles...

thank you

 

[seadolphine2000]

I think that the side without the resistance is a current mirror. Am I right.?

 

[Davood Amerion]

If we not use that output, its resistor not needed anymore. and absence of that resistor not effect on overal behavior of circuit.

Regards,
Amerion

 

[vtshift1]

I think the 2 Rc is for the equivalent circuit model of the diff Amp

 

[mobile-it]

If we not use that output, its resistor not needed anymore. and absence of that resistor not effect on overal behavior of circuit.

Regards,
Amerion

Hi Amerion, this is the answer I like to have but can you explain me a little bit why this absence of this resistor does not effect the behavior of this circuit? Because current is flowing throught the simplest path?

thank you in advance!

 

[Davood Amerion]

In the transistor modeling collector pin behave like current source, and its current depend on base current, not collector resistor.
When we remove collector resistor, nothing hapen!
just transistor consume much power (same current and higher voltage respect to other transistor) and it may negligibly unbalance 2 transistor matching.

Regards,
Davood