Transistor Digital Circuits

active semiconductor devices (with three terminals)

Operating principle: using a voltage between two terminals (command) to control the current through the third terminal.

Transistors: voltage-controlled current sources

TRANSISTORS

• transistors: essential components of every electronic circuit

• Pentium 4 microprocessors : ~ 43,5 million field effect transistors

• Intel 4004, 1971, 10µ, 14mm2, 2300 transistors

• IBM z13, (6-to-8 core), 2015, 22nm, 678mm2, 3,990,000,000 transistors

Discrete transistors

Transistor types

Metal-Oxide-Semiconductor Field-Effect Transistors

Bipolar Junction Transistors

Symbols of the transistors

G - gate or grid D - drainS - source

n - type p - type

n-channel enhancement-type MOSFET

p-channel enhancement-type MOSFET

B – baseC – collector E – emitter

npn BJT pnp BJT

vI = VIH ; T- (on) ; iO > 0 ; vO 0

vI = VIL ; T- (off) ; iO = 0 ; vO > 0

The controlled switches are complementary

Switching Transistor - Controlled switch model

n-channel enhancement-type MOSFET

p-channel enhancement-type MOSFET

npn BJT pnp BJT

Tn

vI

vO

iOTp

vO

iOvI

vI = VIH ; T- (off) ; iO = 0 ; vO >0

vI = VIL ; T- (on) ; iO > 0 ; vO 0

Logic inverter

0V logic 0

VPS logic 1

vA Tn vy

VIL = 0 (off) VPS

VIH = VPS (on) 0

logic 0 - 0V

logic 1 - VPS

Tn and R Tp and R

Logic inverter

Critical analysis of the inverter

with Tn and R

Disadvantage elimination:

R as small as possible, ideal R→0;

Critical analysis of the inverter

withTn and R

Solution: replacement of R with a controlled switch

Disadvantage elimination:

R as small as possible, ideal R→0; R as large as possible, ideal R→∞

Two possible solutions: complementary switches

same input

TTLCMOS

complementary inputs

same switch

MOS transistors BJT transistors and R

MOSFET DIGITAL CIRCUITS

Ideal controlled switch model

Implementation with MOSFET

CMOS Logic Inverter

Logic function NAND, NOR

How can we

eliminate the

disadvantages

due to the

presence of R ?

CMOS NAND

CMOS NOR CMOS AND

Transfer characteristicof the CMOS inverter

Ideal (input) Real

Noise margins

Logic circuit 1

Logic circuit 2

out in

Noise margins - cont.

maxmax

minmin

OLILL

IHOHH

VVNM

VVNM

Voltage levels and

noise margins for

CMOS logic family

supplied at +5V

V1V5.0V5.1 LNM

V1V5.3V5.4 HNM

Bipolar Digital Circuits• Inverter

RTL Technology

RB is always necessary to limit the base current,

due to the presence of the base-emitter pn junction (0.7V voltage drop when Tn is on)

Bipolar Digital Circuits

• Inverter RTL Technology

• NOR

TTL: Transistor-Transistor Logic

• Logic Inverter

• from technological reasons in TTL integrated circuits the use of only npn type transistors is preferred

• identical transistors but complementary control

vI1, vI2 ?

Standard TTL gate

Voltage levels and noise margins for TTL family

Supply only with 5V