This document discusses biasing differential amplifiers using electronic current sources. It explains that electronic current sources are used to stabilize the operating point and increase the effective resistance value to improve the common-mode rejection ratio (CMRR) of differential amplifiers. The current source provides a DC current equal to its specified value while having an output resistance. This allows the current source to be modeled as a DC current source in DC analysis and a resistance in AC analysis. The document is from a lecture on multi-stage and differential amplifiers.

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

2. Biasing with Electronic Current Sources
• Differential amplifiers are biased using electronicV
CC
current sources to stabilise the operating pointRC RC
v
C1 vC2
and increase effective value of R to improveQ2 EEQ1
CMRR.v1
+
-
+
- v2
I
EE
- VEE
• Electronic current source has a DC current equal
to I (or I ) and an output resistance equal toV
DD
EE SS
R (or R ).EE SSRD RD
v
D2
v
D1
M1 M2
• DC model of the electronic current source is a
DC current source, I (or I ) while AC model isv1
+
-
+
v2
- EE SSI
SS
a resistance R (or R ).EE SS-VSS
EE2002 Analog Electronics Multi-Stage and Differential Amplifiers 28

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