Field Effect Transistors (FET)

1
Field Effect Transistors (FET)

• Examples
• Frequency Response

2
Homework

• Chapter 4, FET Transistors due Sep. 24
• 4.12,4.46,4.75,4.96
• Quiz 1 Sep 28 (next Friday)
• Quiz 2 Oct 30
• Project abstracts due October 9 (Tuesday
  following Monday schedule)
• 1 page long, your name, project title, a
  paragraph summary of problem you want to analyze

3
Review of FET operation

• In general, we will use FET in saturation region.
  
• Design ckt,
• ID0.4mA VD1V, Vt2V

4
DC Analysis

• VD1 V , saturation region

5
Biasing Issues

• VGS3V, VGSgtVT
• To establish 1V at drain

6
Biasing (PMOS)

• Design ckt st. 9.9V at the source. Effective
  resistance ro ? (Note PMOS)
• VGS0, VGD-0.1V lt Vt
• Triode region operation

7
Output resistance

• Select
• Find rDS

8
Amplifier Circuit

• Input signal vi
• Output signal vo
• DC bias currents

9
Small Signal Parameters

• Find conductance
• Output resistance

10
Small Signal Gain

• Draw small signal equiv.
• RG very large gt 10M, neglect
• Calculate gain
• Input resistance

11
Frequency response
Internal and external capacitances High-frequency
equivalent circuit model for the MOSFET
(a) High-frequency equivalent circuit model for
the MOSFET when Source is connected to Body (b)

12
Simplified Capacitance Model

• Notice we omit capacitance to Body!

13
MOSFET High Freq. Model
14
Freq. Response CS

• AM ?
• BW?

15
Small-signal equivalent circuit

• (a) equivalent circuit
• (b) the circuit of (a) simplified at the input
  and the output

16
Equivalent circuit

• In the simplified model, we combine the
  capacitances to ground.

17
Low Frequency Resp.

18
Pspice Simulation
19
Frequency Respons