Saturday, March 21, 2015 IEEE @ UCSB 1

ECE 92ECE 92

Projects in Electrical and Computer Engineering

Projects in Electrical and Computer Engineering

Lecture 2

TransistorTransistor

Saturday, March 21, 2015 IEEE @ UCSB 2

• The transistor is a three-terminal semiconductor device.

• Can control electric current or voltage between two of the terminals.

• Used as amplifier or as switch.Field-Effect Transistors

JFET, MESFET

Depletion-mode (normally on)

n-ch p-ch

MOSFET

Depletion-mode (normally on)

Enhancement-mode (normally off)

n-ch p-ch n-ch p-ch

JFETsJFETs

Saturday, March 21, 2015 IEEE @ UCSB 3

Vgs

Gate

Source

Drain

Ids(Vgs,Vds)Vds

Gate

Source

Drain

N-ch JFET

Saturation region ID

Vgs ≤ Vt (cutoff)

Ohmic or Triode region

Vds

Vgs= Vt + 0.5

Vgs= Vt + 1.0

Vgs= Vt + 1.5

Vgs= 0 Idss

Incr

ea

sin

g

Vgs

MOSFETsMOSFETs

Saturday, March 21, 2015 IEEE @ UCSB 4

Vgs

Gate

Source

Drain

Ids(Vgs,Vds)Vds

Gate

Source

Drain

NMOS

Saturation region ID

Vgs ≤ Vt (cutoff)

Ohmic or Triode region

Vds

Vgs= Vt + 0.5

Vgs= Vt + 1.0

Vgs= Vt + 1.5

Vgs= Vt + 2.0

Incr

ea

sin

g

Vgs

BJTsBJTs

Saturday, March 21, 2015 IEEE @ UCSB 5

Base

Emitter

Collector

NPN BJT Ib

Ic=βIB

BC

E

Ic, , mA Forward active region

VCE

70 μA

Incr

ea

sin

g I

b

60 μA

50 μA

40 μA

30 μA

20 μA

10 μA

0 μA

Vce,sat

2

4

6

8

NMOS and PMOSNMOS and PMOS

Saturday, March 21, 2015 IEEE @ UCSB 6

ExampleExample

Saturday, March 21, 2015 IEEE @ UCSB 7

Find W/L and R for the circuit below assuming kn = 100 μA/V2 (transconductance), Vt = 1 V (threshold voltage), and rDS = 40 Ω (drain-to-source resistance).

Op-AmpsOp-Amps

Saturday, March 21, 2015 IEEE @ UCSB 8

• Active circuit element designed to perform mathematica operations of addition, subtraction, multiplication, division, differentiation and integration.

• Useful term: gain=amount of amplification produced by an op-amp. Defined as:

Op-AmpsOp-Amps

Saturday, March 21, 2015 IEEE @ UCSB 9

Op-AmpsOp-Amps

Saturday, March 21, 2015 IEEE @ UCSB 10

ExampleExample

Saturday, March 21, 2015 IEEE @ UCSB 11

+-

Vo

30 kΩ 60 kΩ

60 kΩ30 kΩ

Vs1

Vs2

The switch in the following figure is open. Find v0 in term of the inputs vs1 and vs2. Repeat with the switch closed.