Electronic Devices and Circuits
Engineering Sciences 154

Differential and Multistage Amplifiers

Basic BJT Differential Amplifier

For comparison see NMOS Differential Amplifier
From discussion of bjt physics, we have

which, in turn, allows us to write
Click on images to enlarge
If there is a small resistive mismatch, we can write
or
which allows us to write
For small differential voltage
See an example of a two stage differential amplifier (source)

Basic NMOS Differential Amplifier

For comparison see BJT Differential Amplifier
From our earlier discussion of mos physics, we have
If we make the two devices identical we can write
and we know that
which allows us to write
When we square the bracket term, we get the quadratic equation
 
which has the solutions
Finally, we obtain the normalized form for the transfer function for the differential amplifier.


where we have used from earlier analysis the result that

for each transistor in the pair.

Click on image to enlarge
 
For small differential voltage

Common Mode Rejection Ratio (CMRR):

 
Click on image to enlarge
Click on image to enlarge

 


 

Current Mirrors:

See our current mirror page

Examples of Multi-Stage Amplifiers:

See our multi-stage amplifier page

References:

Extensive notes  from Professor Edgar Sánchez-Sinencio's course Advanced Analog Circuit Design Techniques.  See in particular

Lectures by Professor Roger T. Howe for his course Microelectronics Devices and Circuits.  See also Integrated Microelectronics: An Integrated Approachs

Multistage and Power Amplifiers (local copy) from the course notes of Professor Ralph Mason at Carleton University.

Design of CMOS linear circuits

Amplifiers - Basic Information

On the classification power amplifiers:

Tubes Versus Transistors - Is There an Audible Difference?
Transistor Gain and Configurations
Reading 26 of the Online Radio and Electronics Course

This page was prepared and is maintained by R. Victor Jones
Comments to: jones@deas.harvard.edu.

Last updated December 5, 2001