1. FET AND ITS APPLICATIONS UNIT - III 7/2/2015www.noteshit.com1

2. Field Effect Transistor Family 7/2/2015www.noteshit.com2

3. Construction of an N-channel JFET and the schematic symbol. 7/2/2015www.noteshit.com3

4. Circuit that can be used to measure N-channel JFET characteristics. 7/2/2015www.noteshit.com4

5. Drain characteristics for an ideal representative N-channel JFET. 7/2/2015www.noteshit.com5

6. MOSFETs Depletion-Mode MOSFET Enhancement-Mode MOSFET 7/2/2015www.noteshit.com6

7. MOSFETs Construction of an N-channel depletion-mode MOSFET with external connection for substrate and the schematic symbol. 7/2/2015www.noteshit.com7

8. MOSFETs Construction of an N-channel enhancement-mode MOSFET with external connection for substrate and the schematic symbol. 7/2/2015www.noteshit.com8

9. MOSFETs Drain characteristics for an ideal representative N- channel enhancement-mode MOSFET. 7/2/2015www.noteshit.com9

10. MOSFETs FET Switches JFET Resistance in Ohmic Region N-Channel JFET Switch N-Channel MOSFET Switch 7/2/2015www.noteshit.com10

11. N-channel JFET switch. 7/2/2015www.noteshit.com11

12. Switch using an N-channel enhancement- mode MOSFET. 7/2/2015www.noteshit.com12

13. FET small signal model FETs provide excellent voltage gain high input impedance low-power consumption good frequency range small in size and weight 7/2/2015www.noteshit.com13

14. FET small signal model Transconductance The relationship of VGS (input) to ID (output) is called transconductance. The transconductance is denoted gm. 7/2/2015www.noteshit.com14

15. FET small signal model Graphical Determination of gm 7/2/2015www.noteshit.com15

16. FET small signal model Mathematical Definition of gm gm for VGS =0V: 7/2/2015www.noteshit.com16

17. FET small signal model FET AC Equivalent Circuit 7/2/2015www.noteshit.com17

18. Cascade Connection The output of one amplifier is the input to the next amplifier. The overall gain: Av total : Av1 * Av2 Note the DC bias circuits are isolated from each other by the coupling capacitors. The DC calculations are independent of the cascading. The AC calculations for gain and impedance are interdependent. 7/2/2015www.noteshit.com18

19. FET Cascade Amplifier 7/2/2015www.noteshit.com19

20. Darlington Connection This combination provides large current gain, typically a few thousand. It has a voltage gain of near 1, a low output impedance and a high input impedance. 7/2/2015www.noteshit.com20

21. 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) 7/2/2015www.noteshit.com21

22. Simplified Capacitance Model 7/2/2015www.noteshit.com22

23. Common source Amplifier common-source amplifier is one of three basic single- stage field-effect transistor (FET) amplifier topologies, typically used as a voltage or Tran conductance amplifier. The easiest way to tell if a FET is common source, common drain, or common gate is to examine where the signal enters, and leaves. The remaining terminal is what is known as "common". In this example, the signal enters the gate, and exits the drain. The only terminal remaining is the source. This is a common- source FET circuit. The analogous bipolar junction transistor circuit is the common-emitter amplifier.amplifierfield-effect transistorvoltage or Tran conductance amplifiercommon draincommon gatebipolar junction transistorcommon-emitter amplifier 7/2/2015www.noteshit.com23

24. Common source Amplifier 7/2/2015www.noteshit.com24

25. COMMON DRAIN AMPLIFIER Common-drain amplifier, also known as a source follower, is one of three basic single- stage field effect transistor (FET) amplifier topologies, typically used as a voltage buffer. In this circuit the gate terminal of the transistor serves as the input, the source is the output, and the drain is common to both (input and output), hence its name. The analogous bipolar junction transistor circuit is the common-collector amplifier.amplifierfield effect transistorvoltagebufferbipolar junction transistorcommon-collector amplifier 7/2/2015www.noteshit.com25

26. COMMON DRAIN AMPLIFIER 7/2/2015www.noteshit.com26

27. Freq. Response CS amplifier 7/2/2015www.noteshit.com27

28. Freq. Response CS amplifier 7/2/2015www.noteshit.com28

29. Summary of CS, CG, and CD Amplifiers 7/2/2015www.noteshit.com29

30. Summary of CS, CG, and CD Amplifiers 7/2/2015www.noteshit.com30

31. THANK U 7/2/2015www.noteshit.com31