1. ECE 4991 Electrical and Electronic Circuits Chapter 9

2. 2 Where We Are Chapter 2 - The basic concepts and practice at analyzing simple electric circuits with sources and resistors Chapter 3 – More harder networks to analyze and the notion of equivalent circuits Chapter 4 – Capacitors and inductors added to the mix Chapter 5 – Analyzing transient situations in complex passive networks Chapter 8 – New subject – the wonders of operational amplifiers as system elements Chapter 9 – Introduction to semiconductors – the basics and diodes – more network analysis Chapter 10 – Bipolar junction transistors and how they work – now you can build your own op amp

3. 3 What’s Important in Chapter 9 1.Definitions 2.Semiconductor basics 3.Diode behavior 4.Ideal diode model 5.Offset diode model 6.Diodes in circuits

4. 4 1. Definitions Semiconductor Diode Majority Carrier Minority Carrier Forward bias Reverse bias Ideal model Offset model

5. 5 2. Semiconductor Basics Metals are a “sea of electrons” – conduct electricity extremely well Insulators have no available charge carriers to make an electric current Semiconductors are in between Silicon

6. 6 Semiconductor Basics Silicon can be “doped” to provide charge carriers – either negative or positive –N-type or P-type One-part-per-million doping is normal –~ 1 x 10 16 /cm 3

7. 7 What’s a diode? A volume of n-type silicon touching a volume of p-type silicon forms a “diode” Electric current flows easily in one direction but not in the reverse direction This is the electronic symbol for a diode (P N)

8. 8 Why do they work the way they do? Which leads to the diode equation P side N side

9. 9 How to make a diode Start with p-type silicon Grow silicon dioxide (glass) Pattern and etch a hole in the oxide Dope the exposed silicon n-type and diffuse it into the substrate Apply metal contacts to top and bottom p-type Si SiO 2 2 n-type Si

10. 10 3. Diode behavior Plot diode current versus diode bias

11. 11 There are two types of diode reverse breakdown Avalanching –Caused by strong electric fields in the diode –Impact ionization – chain reaction Zener Breakdown –Quantum mechanical effect –Can be set and controlled very tightly –Used in circuits to set voltages – usually in the 5 to 25 volt range.

12. 12 Diode Breakdown

13. 13 4. Ideal Diode Model Forward bias –Diode turns on hard at zero volts Reverse bias –Zero current independent of bias Ideal Diode Model

14. 14 Offset Diode Model 5. Offset Diode Model Forward bias –Diode turns on hard at 0.6 volts Reverse bias –Zero current independent of bias

15. 15 For Either Model… Reverse breakdown is abrupt, at either the Zener or the avalanche voltage Or

16. 16 6. Diodes in Circuits Diodes are often found in LCR circuits Use a simple model for the diode in the circuit –Ideal –Offset Circuit analysis by hand involves some initial guesswork –Is it conducting or not?

17. 17 An ideal diode in a circuit V D R V D R V D R + + + V D  0 V D < 0

18. 18 An offset model diode behaves like an ideal diode in series with a battery Offset model diode 0.6 volt battery + = Ideal diode

19. 19 An offset model diode in a circuit V D R V D R V D R + + + V D  0.6 V V D < 0.6 V + 0.6 V

20. 20 A Zener diode in a circuit V D R + 0 < V D < V Z DV R + V D  V Z +V Z V D V R + V D R +

21. 21 Procedure for Circuit Analysis 1.Think about the circuit, then assume a conduction state (on, off, or zenering) 2.Substitute in the assumed diode model 3.Solve the circuit 4.Figure out the resultant diode current and voltage 5.If consistent with assumption, congrats! If not, try again with another assumption

22. 22 Practice with Circuits

23. 23 Practice with Circuits

24. 24 Practice with Circuits

25. 25 Practice with Circuits

26. 26 Practice with Circuits

27. 27 Practice with Circuits

28. 28 Practice with Circuits