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Field Effect Transistors and their applications. Types of Field Effect Transistors. There are Junction FETs (JFET) and Insulated gate FETs (IGFET) There are many types of IGFET. Most common is the MOSFET: Metal Oxide Semiconductor FET. A silicon atom (Si). Has 4 outer electrons

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Presentation Transcript
slide2
Types of Field Effect Transistors

There are Junction FETs (JFET) andInsulated gate FETs (IGFET)There are many types of IGFET. Most common is the MOSFET: Metal Oxide Semiconductor FET.

a silicon atom si
A silicon atom (Si)

Has 4 outer electrons

The outer electron shell needs 8 to be “full”

(standing wave pattern)

Silicon will try to lend or borrow 4

an arsenic atom as
An Arsenic atom (As)

Has 5 outer electrons

One surplus for fitting in to the lattice

a gallium atom ga
A Gallium atom (Ga)

Has 3 outer electrons

One short for fitting in to the lattice

what causes the depletion
What causes the depletion?
  • Electrons move from left to right to fill the + holes
  • Where electrons and holes combine the area is “depleted” of current carriers
  • This leaves the left (N Type) positive so eventually this prevents the depletion spreading any more.
  • Applying negative to N type replaces the depleted carriers and the current resumes (Forward biased diode)
  • Applying positive to the N type removes more electrons and increases the depletion. Almost no current flows. (Reverse biased diode)
the junction transistor
The junction transistor

Emitter (-)

Collector (+)

Electrons

Base

Electrons are negative 

(Original patent used point contact)

npn transistor circuits
NPN Transistor circuits
  • Common base
  • Emitter follower (common collector)
  • Common emitter

Collector

Base

Emitter

slide15
Types of Field Effect Transistors

There are Junction FETs (JFET) andInsulated gate FETs (IGFET)There are many types of IGFET. Most common is the MOSFET: Metal Oxide Semiconductor FET.

slide17
Field Effect Transistors come in 4 forms

N Channel (as an NPN transistor or Valve)P Channel (as a PNP transistor) N and P channel each come as:Enhancement mode (just IGFET)Depletion mode (IGFET or JFET)

curve l 10v gate mostly resistive curve a 2 5v gate mostly constant current pinchoff
Curve L = 10v gateMostly resistiveCurve A = 2.5v gateMostly constant current (pinchoff)

BSS 145 N channel enhancement FET output curves

L

A

slide28
FETs in the SoftRock Receiver

The I & Q generator uses 4 D type Flip Flops 74HC74

The dual I/Q Mixer uses an FST 3253 dual 4 way multiplexer switch

These all use logic circuits built with FETs

Lets look at basic logic

slide29
Logic circuits

By combining together enough NAND gates you can build anything digital. So that includes computers.

(However some other bits may make life easier)

We will look at how to make the Flip Flops used in the I / Q generator another time.

So lets look at a CMOS NAND gate.

Complementary Metal Oxide Semiconductor FET

(We will add an inverter to make an AND gate too)

slide32
NAND gate IC Layout

(From Wikimedia commons)

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