Week #1 Review of Transistors

1. Week #1 Review of Transistors ENG3640 Microcomputer Interfacing

2. Topics • Semiconductors • PN Junction (Diodes) • Bi-Polar Junction Transistors (BJTs) • MOS Transistors (nMOS/pMOS) • CMOS Technology • Interfacing TTL with CMOS ENG3640 Fall 2012

3. Semiconductor Materials • Electronic materials generally can be divided into three categories: • Insulators • Semiconductors • Conductors • The primary parameter used to distinguish among these materials is the resistivity (rho) • Insulator 105 < rho • Semiconductors 10-3 < rho < 105 • Conductors rho < 10-3 • Silicon and germanium are the most important semiconductor materials ENG3640 Fall 2012

4. P-type and N-type • The real advantage of semiconductors emerge when impurities are addedto the material in minute amounts (Doping) • Impurity doping enables us to change the resistivityover a very wide range and determine whether the electron or hole population controls the resistivity of the material. • Donor Impurities: have five valence electrons in the outer shell (phosphorus and arsenic). Semiconductors doped with donor impurities are called n-type. • Acceptor Impurities: have one less electron than silicon in the outer shell (boron). Semiconductors doped with acceptor impurities are called p-type. ENG3640 Fall 2012

5. Diodes: PN Junction The diode is the simplest and most fundamental nonlinear circuit element. Diffusion of majority carriers into the opposite sides causes a depletion region to appear at the junction. The diode essentially allows an electric current to flow in one direction and locks it in the other direction ENG3640 Fall 2012

6. Diodes i = IS(e (v/nVT) - 1) i = -IS IS = Saturation Current VT = Thermal Voltage v = Terminal voltage n = Constant (1) ENG3640 Fall 2012

7. Diodes: Applications Half-wave Rectifier with resistive load. ENG3640 Fall 2012

8. Transistors: MOSFET vs. BJT drain collector NPN bipolar transistor N-channel MOSFET body base gate emitter source Bi-Polar Junction Transistor Current Controlled Switch Uni-Polar Junction Transistor Voltage Controlled Switch ENG3640 Fall 2012

9. History of Transistors • 1940: Ohl develops the PN Junction • 1945: Shockley's laboratory established • 1947: Bardeen and Brattain create point contact transistor (U.S. Patent 2,524,035) ENG3640 Fall 2012

10. collector collector base base emitter emitter BJT Symbols PNP Bipolar Transistor NPN Bipolar Transistor ENG3640 Fall 2012

11. Bipolar Junction Transistor • Acts like a current controlled switch. • If we put a small current into the base then the switch is on (i.e. current may flow between collector and emitter) • If no current is put into the base, switch is off. • Regions of operations • Cutoff • Active • Saturation ENG3640 Fall 2012

12. BJT Modes of Operation ENG3640 Fall 2012

13. BJT: BipolarJunction Transistor • A current controlled device • Two types: NPN and PNP • Handles more current than MOSFETs (Faster) • More difficult to manufacture • Dissipates more power • Achieves less density on an IC • Does not have full swing voltage ENG3640 Fall 2012

14. The MOS TransistorMetal Oxide Semiconductor Polysilicon Aluminum ENG3640 Fall 2012

15. MOS: Operation ENG3640 Fall 2012

16. nMOS vs. pMOS Devices ENG3640 Fall 2012

17. MOSFET: MetalOxide Semiconductor FieldEffectTransistor • A voltage controlled device • Two types: NMOS and PMOS • Handles less current than a BJT (Slower) • Easier to manufacture • Dissipates less power • Achieves higher density on an IC • Has full swing voltage 0  5V ENG3640 Fall 2012

18. Gordon Moore Intel Co-Founder and Chairmain Emeritus Image source: Intel Corporation www.intel.com VLSI Trends: Moore’s Law • In 1965, Gordon Moore predicted that transistors would continue to shrink, allowing: • Doubled transistor density every 18-24 months • Doubled performance every 18-24 months • History has proven Moore right • But, is the end is in sight? • Physical limitations • Economic limitations ENG3640 Fall 2012

19. Technology Evolution ENG3640 Fall 2012

20. NMOS Transistors in Series/Parallel Connection • Transistors can be thought as a switch controlled by its gate signal • NMOS switch closes when switch control input is high NMOS Transistors pass a ``strong” 0 but a ``weak” 1 ENG3640 Fall 2012

21. PMOS Transistors in Series/Parallel Connection PMOS Transistors pass a ``strong” 1 but a ``weak” 0 ENG3640 Fall 2012

22. Complementary MOS (CMOS) • NMOS Transistors pass a ``strong” 0 but a ``weak” 1 • PMOS Transistors pass a ``strong” 1 but a ``weak” 0 • Combining both would lead to circuits that can pass strong 0’s and strong 1’s C Y X C ENG3640 Fall 2012

23. Static Complementary CMOS PUN and PDN are dual logic networks VDD In1 PMOS only In2 PUN … InN F(In1,In2,…InN) In1 In2 PDN … NMOS only InN VSS • At every point in time (except during the switchingtransients) each gate output is connected to eitherVDD or VSS via a low resistive path ENG3640 Fall 2012

24. CMOS Inverter Pull-up Network Pull-down Network ENG3640 Fall 2012

25. CMOS Inverter ENG3640 Fall 2012

26. CMOS Inverter ENG3640 Fall 2012

27. Types of Outputs • There are different types of outputs associated with digital circuits • Totem Pole (normal output) • Tri-state (High, Low, High Impedance) • Open Collector or Open Drain ENG3640 Fall 2012

28. 1. Totem Pole (normal output) Pull-up Network • Simply refers to the vertical alignment of components • Q1, Q2 act as switches controlled by Input A • When One transistor is on the other is off • Q1 is pull-up, Q2 is pull-down • Not possible to join totem pole outputs together. Pull-down Network ENG3640 Fall 2012

29. 2. Tri-State Output • Tri-state gates enable a device to electrically disconnect its output when it is not driving the bus. A E Y E ENG3640 Fall 2012

30. 3. Open Collector • As with tri-state output, open collector outputs allow multiple logic devices to drive the same line. • Since the pull-up transistor is missing, the circuit has the capability of pulling the signal down. • To pull a signal up we need an EXTERNAL RESISTOR (passive pull-up to high level) Low to high transitions are much slower for open drain gate than for standard gate with active pull-up * Pull-down Network ENG3640 Fall 2012

31. Open Collector: IRQ • Most common use of open collector is to connect several devices to a common interrupt line. +5V * I/O Device A IRQ I/O Device B * MCU ENG3640 Fall 2012

32. Logic Families • RTL, DTL earliest • TTL was used 70s, 80s • Still available and used occasionally • 7400 series logic, refined over generations • CMOS • Was low speed, low noise • Now fast and is most common • BiCMOS and GaAs • Speed ENG3640 Fall 2012

33. Resistor-Transistor Logic (RTL) ENG3640 Fall 2012

34. TTL (Transistor-Transistor) Q1 In Q2 In Q1 Q2 Out 0 ON OFF 1 1 Off ON 0 ENG3640 Fall 2012

35. CMOS/TTL Interfacing • Several factors to consider • Noise Margin CMOS (VOL = 0, VOH = 5V) TTL (VIL = 0.4 V, VIH = 2.4V) CMOS TTL No problem for CMOS to drive TTL since CMOS has full swing output ENG3640 Fall 2012

36. CMOS/TTL Interfacing TTL (VOL = 0.7 V, VOH = 3.3V) CMOS (VIL = 2.3, VIH = 3.3V) TTL CMOS • We do have a problem when TTL drives CMOS. • TTL driving HC (high speed CMOS) doesn’t work unless the TTL high output happens to be higher and the CMOS high input threshold happens to be lower by a total of 1V. • To drive CMOS inputs properly from TTL outputs, the CMOS device should be TTL compatible (i.e. use HCT, VHCT, FCT) ENG3640 Fall 2012

37. CMOS/TTL Interfacing Other factors to consider (2) Fan-out: defined as Min( IOH/IIH, IOL/IIL) We would encounter problems when CMOS drives TTL since CMOS has limited driving current. CMOS TTL ENG3640 Fall 2012

38. CMOS/TTL Interfacing • CMOS has very high input impedance so almost no current is required in either state! • So TTL can drive CMOS with no problems if we are considering fan-out (up to 15 gates) TTL CMOS ENG3640 Fall 2012

39. Extra Slides ENG3640 Fall 2012

40. History of MOS Transistors • 1961: TI and Fairchild introduce the first logic ICs ($50 in quantity) • 1962: RCA develops the first MOS transistor RCA 16-transistor MOSFET IC Fairchild bipolar RTL Flip-Flop ENG3640 Fall 2012

41. Bell Labs • 1951: Shockley develops a junction transistor manufacturable in quantity (U.S. Patent 2,623,105) ENG3640 Fall 2012

42. BJT Operating Regions For different values of VBE ENG3640 Fall 2012

43. BJT in Cutoff Region • VBB is smaller than 0.5V • Under this condition iB= 0 • As a result iC becomes negligibly small • Both base-emitter as well base- collector junctions may be reverse biased • Under this condition the BJT can be treated as an off switch ENG3640 Fall 2012

44. BJT in Active Region • VBB is above 0.5V around 0.7V • Under this condition iB= (VBB – VBE)/RBB • As a result iC =  IB • EBJ is forward • CBJ is reverse ENG3640 Fall 2012

45. BJT in Saturation Region • Both base emitter as well as base collector junctions are forward biased. • VCE 0.2 V • Under this condition the BJT can be treated as an on switch ENG3640 Fall 2012

46. BJT in Saturation Region • A BJT can enter saturation in the following ways: • For a particular value of iB,if we keep on increasing RCC • For a particular value of RCC,if we keep on increasing iB • For a particular value of iB,if we replace the transistor with one with higher  ENG3640 Fall 2012

47. BJT: Active Region Bias Current flow in an NPN transistor biased to operate in the active mode. ENG3640 Fall 2012

48. NPN BJT Current flow IE = IC +IB ? ENG3640 Fall 2012

49. BJT ( and ) • From the previous figureiE = iB + iC • Define  = iC / iE = 0.99 • Define  = iC / iB = 100 • Then  = iC / (iE –iC) =  /(1- ) • TheniC =  iE; iB = (1-) iE • Typically   100 for small signal BJTs (BJTs that handle low power) operating in active region (region where BJTs work as amplifiers) ENG3640 Fall 2012

50. (1) Totem Pole, BJT • Simply refers to the vertical alignment of components • Q1, Q2 act as switches controlled by In • When One transistor is on the other is off • Q1 is pull-up, Q2 is pull-down • Not possible to join totem pole outputs together. In Q1 In Q1 Q2 Out 0 ON OFF 1 Q2 1 Off ON 0 ENG3640 Fall 2012