Lecture Notes on BJTs, Lecture notes of Computer Engineering and Programming

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Digital logic

Bipolar Junction Transistor (BJT)

MOS Field Effect Transistor (MOSFET)

Effect of capacitance

Buzzer

1

EE 445L – Embedded System Design Lab

2

Digital Logic Families

Input

Q

Q

+ 3. 3 V

Q

Q

Output

V

OH I VIH

I

I

+ 3. 3 V

V

I

V

V

OH

I

OH

3. 3 V

I

IH

I

• V

OH

³ V

IH

• I

OH

³ I

IH

4

Digital Logic Families

• Logic voltage levels

– V

IL

– voltage below which an input is considered logic low

– V

IH

- voltage above which an input is considered logic high

– V

OH

– output voltage for a logic high (current less than I

OH

– V

OL

- output voltage for a logic low (current less than I

OL

V

OL

£ V

IL

V

OH

³ V

IH

7

Digital Logic (MOS-TTL(BJT))

Output High State

• The device providing

(driving) the output is

capable of sourcing a

maximum current to that

output

• (^) I OH

• Each input device

receiving (sinking) the

output as an input

requires a maximum

current:

• (^) I IH (^) For more information read Section 1.4 in the book S G D

3. 3 V IOH VOH Input Output R IIH
4. 3 V Input R IIH
5. 3 V

9

Digital Logic Families

The following five parameters most

affect our choice of logic families:

– power supply voltage

– power supply current

– speed

– output drive, I

OL

, I

OH

– noise immunity

10

Logic Families

Family Example IOH IOL IIH IIL Standard TTL 7404 0.4 mA 16 mA 40 μA 1.6 mA Schottky TTL 74S04 1 mA 20 mA 50 μA 2 mA Low Power Schottky 74LS04 0.4 mA 4 mA 20 μA 0.4 mA High Speed CMOS 74HC04 4 mA 4 mA 1 μA 1 μA Adv High Speed CMOS 74AHC04 4 mA 4 mA 1 μA 1 μA TM4C 2mA-drive TM4C123 2 mA 2 mA 2 μA 2 μA TM4C 4mA-drive TM4C123 4 mA 4 mA 2 μA 2 μA TM4C 8mA-drive TM4C123 8 mA 8 mA 2 μA 2 μA TM4C 12mA-drive TM4C1294 12 mA 12 mA 2 μA 2 μA For more information read Section 1.4 in the book

NPN Transistor Model

• (^) 1) Normally Vc > Ve
• (^) 2) Current can only flow in the following directions
  • (^) from base to emitter (input current)
  • (^) from collector to emitter (output current)
  • (^) from base to collector
    • (^) (doesn’t usually happen, but could if Vb > Vc)
• (^) 3) Each transistor has maximum values that should not be exceeded
  • (^) Ib Ic Vce and Ic•Vce
• (^) 4) The transistor acts like a current amplifier
  • (^) Ic = hfe•Ib
• (^) 5) The transistor will saturate if Vb > Ve + Vbe(SAT)
  • (^) where Vbe(SAT) is typically above 0.6V 12 For more information read Section 1.4 in the book PN2222 Lab 3 TIP120 Lab 10 Reverse active Cutoff Saturatio n Forwar d active VBE VBC E < B < C E < B > C E > B < C E > B > C

13

Transistors

Type NPN PNP package (^) Vbe(SAT) Vce(SAT) hfe min/max Ic general purpose 2N3904 2N3906 TO-92 0.85 V 0.2 V 100 10mA general purpose PN2222 PN2907 TO-92 1.2 V 0.3 V 100 150mA general purpose 2N2222 2N2907 TO-18 1.2 V 0.3 V 100/300 500mA power TIP29A TIP30A TO-220 1.3 V 0.7 V 15/75 1A power TIP31A TIP32A TO-220 1.8 V 1.2 V 25/50 3A power TIP41A TIP42A TO-220 2.0 V 1.5 V 15/75 3A Darlington TIP120 TIP125 TO-220 2.5 V 2.0 V 1000 min 3A PN2222 Lab 3 TIP120 Lab 10

Lab 3 Speaker Interface

• (^) Assume TM4C output at 3.3V
• (^) At saturation (maximum loudness)
  • (^) V BE = 1.2V^ and^ VCE = 0.3V
• (^) Ohms Law across speaker
  • (^) I CE = (3.3-0.3V)/32W = 94mA (near maximum!)
  • (^) P = I CE (^2) *32W = 0.28 watts (too loud)
• (^) Transistor gain is 100
  • (^) I B =I CE /100 = 1mA
• (^) Ohms Law across input resistor
  • (^) R = (3.3-1.2V)/0.001A = 2000W
    • (^) What if R = 10kW?
      • (^) I B =(3.3-1.2V)/10000W = 0.21mA
      • (^) h ie = 2k W (not a fixed value)
      • (^) I B =VOH/(R +hie) =3.3V/(10000W +2000W)= 0.28mA
    • (^) Transistor gain is 100
      • (^) I CE =I B *100 = 21mA
      • (^) P = I CE 2 *32W = 0.015 watts
      • (^) quiet Use data sheet to guess Measure with voltmeter

Capacitance

0 V 1 time

3. 3 0 T V 1 V 2 Input C V 2 Output R V 1 V = 3. 3 - 3. 3 e 2

• t/(RC) Slew rate

2. 0
3. 3 Transition time Capacitance loading is an important factor when interfacing CMOS devices

• Make it run faster

– Decrease R,C

– Increase I, P

• Make it less noisy

– Decrease slew rate

• Saturated Mode

• Current gain h

fe

• Activation V

be

• Output V

ce

I

ce

• Capacitance

– Slows down

– Reduces EM emissions

Summary

18

Output

TM 4 C

R

speaker

1 N 914

PN 2222

Base

Collector

Emitter