1. Field Effect Transistors and their applications

2. 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. Types of Field Effect Transistors

3. 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

4. Silicon (group 4) bonds

5. A pure silicon crystal lattice

6. An Arsenic atom (As) Has 5 outer electrons One surplus for fitting in to the lattice

7. Arsenic doping (group 5) – N type

8. A Gallium atom (Ga) Has 3 outer electrons One short for fitting in to the lattice

9. Gallium doping (group 3) – P type Holes are positive

10. A P-N Junction (N on left)

11. 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)

12. The junction transistor Emitter (-) Collector (+) Base (Original patent used point contact) Electrons Electrons are negative 

13. NPN Transistor circuits Common base Emitter follower (common collector) Common emitter Base Collector Emitter

14. A Planar NPN junction transistor CollectorBaseEmitter

15. 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. Types of Field Effect Transistors

16. An Insulated Gate FET

17. 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) Field Effect Transistors come in 4 forms

18. Transistor symbols

19. In an IC the substrate can be separate

20. Insulated Gate Field Effect Transistor N Channel Enhancement mode

21. N channel enhancement IGFET turned on

22. N enhance FET at Pinchoff

23. N enhance FET beyond Pinchoff

24. Curve L = 10v gate Mostly resistive Curve A = 2.5v gate Mostly constant current (pinchoff) BSS 145 N channel enhancement FET output curves A L

25. N channel Depletion mode FET ON – No gate bias

26. N channel Depletion mode FET off

27. An application: The SoftRock Receiver

28. 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

29. 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)

30. An AND gate (NAND + Inverter) AND NAND AB

31. Simulated AND gate waveforms AND NAND B A

32. NAND gate IC Layout (From Wikimedia commons)

33. SoftRock Receiver

35. LTSpice model of SoftRock Receiver

36. LTSpice output of SoftRock model

37. Questions?