This document discusses differential amplifiers and multi-stage amplifiers. It defines a differential amplifier as having two transistors in a symmetrical configuration with two inputs and two outputs. An ideal differential amplifier uses perfectly matched transistors. It also discusses common-mode rejection ratio (CMRR), which measures an amplifier's ability to amplify a desired differential-mode input signal while rejecting an undesired common-mode input signal. Higher CMRR indicates better rejection of common-mode signals. Differential amplifiers form the core of operational amplifiers.

1. Part 2.2
Multi-Stage and
Differential Amplifiers
Assoc Prof Zheng Yuanjin email: yjzheng@ntu.edu.sg
EE2002 Analog Electronics

2. Differential Amplifiers
Piezoelectric Transducers
Strain GaugeCase
Epoxy
plotting
Backing
material
Electrodes
Piezoelectric
element
Thermal Couple
Thermocouple Lead
wire
Gage
A+
Vout
B
Target
surface
Ice bath
(known constant
temperature for
reference)
Reference
junctions
Ref.
EE2002 Analog Electronics Multi-Stage and Differential Amplifiers 15

3. Differential Amplifiers
V
CC
V
DD
RC vC1
Q1
RC
R
DRD
v
C2 vD1
v
D2
Q2 M1 M2
+
-
v1v1
+
- v2
+
-
+
-
v
2
R
EE R
SS
- VEE -VSS
• Differential amplifier forms the heart of operational amplifier.
• It contains two transistors in symmetrical configuration.
• It has two inputs and two outputs.
• Ideal differential amplifier uses perfectly matched transistors.
EE2002 Analog Electronics Multi-Stage and Differential Amplifiers 16

10. Common-mode Rejection Ratio (CMRR)
• Measures ability of amplifier to amplify desired differential-mode input signal
and reject undesired common-mode input signal.
• For differential output, since A = 0, CMRR = .cm-diff
• For single-ended output,
g Rm CA
dm-se 2CMRR    g R
R m EE
A Ccm-se
2REE
EE2002 Analog Electronics Multi-Stage and Differential Amplifiers 23

11. Multi-Stage and
Differential Amplifiers
-End of Lecture-