Transistor Digital Circuits

Controlled switch model

vCT > VCTex; T- (on); iO > 0; vO 0

vCT < VThn; T- (off); iO = 0; vO = VPS

vCT > VThp ; T- (off); iO = 0; vO = VPS

vCT < VCTex; T- (on); iO > 0; vO 0

The Tn and Tp controlled switches are complementary

TpTn

Switching

Transistor

Model

(on) (on)

TpTn

Switching

Transistor

Model

vCT Tn Tp

L (Low) (off) (on)

H (High) (on) (off)

The Tn and Tp controlled switches are complementary

Analog vs. logic signal

analog signal digital signal

Logic 0 false low

Logic 1 true high

0V → logic 05V → logic 1 CMOS logic family

supplied at +5V

Transistors: essential components of every electronic circuit

Integrated transistors - digital integrated circuit

Transistor (T) count

• Intel 4004, 1971, 10µ, 12mm2, 2,300 T

• Pentium 4 Prescott: 2004, 90nm, 143mm2 112,000,000 T

• Core i7 Broadwell-E (10-core), 2016, 14nm, 246mm2, 3,200,000,000 T

• Apple A12 (hexa-core ARM64), 2018, 7nm, 83.27mm2, 6,900,000,000 T

• GC2 IPU, 2018, 16nm, 825mm2, 23,600,000,000 T

- Intelligence Processing Unit (IPU), specifically designed for artificial intelligence (machine learning)

[https://en.wikipedia.org/wiki/Transistor_count]

MOSFET DIGITAL CIRCUITS

➢ Ideal controlled switch model

➢ Implementation with MOSFET

Logic inverter

0V → logic 0 (Low)

VPS → logic 1 (High)

vA Tn vy

0 (off) VPS

VPS (on) 0

logic 0 - 0V

logic 1 - VPS

Tn and R Tp and R

Logic inverter

A

Y

R

Tn

VPS

Logic invertor: MOSFET and R

n -type channel MOSFET

A

Y

R

Tp

VPS

p -type channel MOSFET

Critical analysis of the logic 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 transitors BJT transitors and R

CMOS Logic Inverter

vGSn=vI

vGSp=vI-VDD

Logic function NAND, NOR

a) What is the truth table?b) What are the states of the switches?c) How can we eliminate the disadvantages due to the presence of R ?

Problems

Logic function NAND, NOR

CMOS NAND

a) What is the truth table?b) What are the states of alltransistors?

Problem

CMOS NAND

CMOS NOR CMOS AND

19

Transfer characteristicof the CMOS inverter

Ideal (input) Real

Noise margins

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

Logic circuit 1

Logic circuit 2

out in

BJT DIGITAL CIRCUITS

➢ RTL technology

➢ TTL technology

Switching BJT, digital circuitRB resistor to limit the base current

B

Co

B

BECoB

R

v

R

Vvi

7.0−=

−=

Cex

Bsat

ii =

C

PS

C

CEsatPSCex

R

V

R

vVi

2.0−=

−=

T – (off), if vCo< 0.6V

T – (on), if iB > iBsat

Problem

V5;150

;k2;k100

==

==

PS

CB

V

RR

a) What is the state of T if vCo = 0V? What is the vCE value?

b) What is the state of T if vCo = 5V? What is the vCE value?

c) What is the vCo range to keep T off? What about to keep

it in saturation?

d) If 0V => logic 0 and 5V => logic 1, what is the logic

function of the circuit if ]V}[5;0{Cov

Bipolar Digital Circuits

• Inverter RTL Technology

• NOR

a) What is the schematic for the 2-input NAND gate in a RTL technology?b) What is the truth table?c) What are the states of the transistors?

Problem

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

TTL sub-families with improved performances

Schottky transistor Schottky diode: a metal to semiconductor junction, in conduction 0,5V

vBE=0,8V; vBC=0,5V; vCE=0,3V

• Schottky transistor doesn't enter saturation mode

• increases the commutation speed

Simplified structure of a 2-input NAND gate from the Low-power Schottky family

Logic Gates

0 1

1 0

NOT AB

0 0 0

0 1 0

1 0 0

1 1 1

AND

0 0 0

0 1 1

1 0 1

1 1 1

OR

A+B

Logic Gates – cont.

0 0 1

0 1 1

1 0 1

1 1 0

0 0 1

0 1 0

1 0 0

1 1 0

NORNAND

0 0 0

0 1 1

1 0 1

1 1 0

XOR

Analog Switch (AS)

The AS is an electronic circuit that allows or blocks an input signal to pass to the output of the circuit according to a control signal.

vCo - two levels: VCoL<VTh and VCoH>VCTex

vCo=VCoL ; Tn-(off) ; vO=0

vCo=VCoH ; Tn- (exc) ; vO= vI

no power consumption

VThpVThn

Bidirectional AS with two complementary

controlled switches

vCo=VCoL ; AS - (off) ;

vCo=VCoH ; AS - (on) ;

C=0; AS - off; vO=0

C=1; AS - on; vO=vI

IC 4066 –4 transmission gates; supplied at 10V, ron=150Ω

DG400 (Siliconics) ron=20Ω

VCoH=VDD; VCoL=VSS

vI (VSS; VDD)

AS

AS – CMOS implementationbidirectional transffer

Application: three-channel MUX

What is the output voltage in each of the three situations? Justify the answer.

Application: three-channel MUX