differential amplifier

[legend killer]

Hi everyone,
I am studying diffrential amplifier and opamps.
I am having confusion regarding the commom emitter resistor of differential amplifier.Why d0 we need to conmbine the two emitters.What difference will it make if we connect two different resistors with each emitter.

 

[bychon]

The emitter resistor forces the 2 transistors to share one current flow. If one transistor has a higher current through its base, it will turn on and the other will turn off. Another way to look at it is to call the first transistor a common emitter configuration and call the second transistor a common base configuration. As the first transistor adds current to the emitter resistor, the emitter of the second transistor is driven to a higher voltage compared to its base, and gets shut off.

 

[ericgibbs]

Hi everyone,
I am studying diffrential amplifier and opamps.
I am having confusion regarding the commom emitter resistor of differential amplifier.Why d0 we need to conmbine the two emitters.What difference will it make if we connect two different resistors with each emitter.

hi,
The answers in the name 'differential'.
Its a difference amplifier, its the difference of the voltage on base1 and base2 that is amplified and the amplified difference appears at collector1 and collector2.

If only base1 is driven by an external voltage the signal is coupled via its emitter1 to the emitter2.
Base2 can be held at a steady voltage, so the emitter1 signal thru to the emitter2 appears as signal of the opposite polarity/sense to the signal on base1.

So on the collectors you have a 'push pull' signal.

The common emitter resistor connects the two emitters together.
OK

 

[legend killer]

that means two different resistors will not make a difference amplifier

 

[ericgibbs]

that means two different resistors will not make a difference amplifier

Thats correct, do you have an image of a particular diff amp you want to analyse.?

 

[legend killer]

hi,
The answers in the name 'differential'.
Its a difference amplifier, its the difference of the voltage on base1 and base2 that is amplified and the amplified difference appears at collector1 and collector2.

If only base1 is driven by an external voltage the signal is coupled via its emitter1 to the emitter2.
Base2 can be held at a steady voltage, so the emitter1 signal thru to the emitter2 appears as signal of the opposite polarity/sense to the signal on base1.

So on the collectors you have a 'push pull' signal.

The common emitter resistor connects the two emitters together.
OK

Actually I didnt understand properly
Can u please explain in some detail
or suggest a good website

 

[ericgibbs]

Actually I didnt understand properly
Can u please explain in some detail
or suggest a good website

Hi LK,
I little bedtime reading..

 

[legend killer]

Hi LK,
I little bedtime reading..

Thank you very much for that Eric