1. Chapter 13 Small-Signal Modeling and Linear Amplification
Microelectronic Circuit Design
Richard C. Jaeger
Travis N. Blalock
Microelectronic Circuit Design, 3E
McGraw-Hill

2. Small-Signal Model of BJT
Using 2-port y-parameter network,
The port variables can represent either time-varying part of total voltages and currents or small changes in them away from Q-point values.
bo is the small-signal common-emitter current gain of the BJT.
Jaeger/Blalock
7/20/07
Microelectronic Circuit Design, 3E
McGraw-Hill

3. Microelectronic Circuit Design, 3E
Hybrid-Pi Model of BJT
Transconductance:
Input resistance:
The hybrid-pi small-signal model is the intrinsic representation of the BJT.
Small-signal parameters are controlled by the Q-point and are independent of geometry of the BJT
Output resistance:
Jaeger/Blalock
7/20/07
Microelectronic Circuit Design, 3E
McGraw-Hill

4. Microelectronic Circuit Design, 3E
Equivalent Forms of Small-Signal Model for BJT
Voltage -controlled current source gmvbe can be transformed into current-controlled current source,
Basic relationship ic = bib is useful in both dc and ac analysis when BJT is in forward-active region.
Jaeger/Blalock
7/20/07
Microelectronic Circuit Design, 3E
McGraw-Hill

5. Small-Signal Model for the MOSFET
Using 2-port y-parameter network,
The port variables can represent either time-varying part of total voltages and currents or small changes in them away from Q-point values.
Microelectronic Circuit Design, 3E
McGraw-Hill

6. Small-Signal Parameters of MOSFET
Transconductance:
Output resistance:
Since gate is insulated from channel by gate-oxide input resistance of transistor is infinite.
Small-signal parameters are controlled by the Q-point.
For same operating point, MOSFET has higher transconductance and lower output resistance that BJT.
Amplification factor for lVDS<<1:
Microelectronic Circuit Design, 3E
McGraw-Hill