Chapter 7: Building Blocks integrated-Circuit Amplifiers

IC Design Philosophy Discrete Circuit v.s. Integrated Circuit Constraints for IC

Large- and moderate-value resistors Large capacitors

Opportunities for IC Constant-current sources Very small capacitors (in the picofarad and fraction of

a picofarad range)

Comparison of the MOSFET and BJT MOSFET

CMOS: the most widely used IC technology for both digital and analog as well as mixed-signal applications

Practical infinite input resistance Can be made quite small Manufacturing process is relatively simple

BJT Higher output currents High reliability under severe environmental

conditions, such as in the automotive industry

6.3 IC Biasing

iD – vDS Characteristics

area gateunit per eCapacitanc :

electrons ofmobility :

)(A/V

region)n (Saturatio 2

1

region) Triode(2

1

2'

2'

2'

ox

n

oxnn

tGSnD

DSDStGSnD

C

Ck

VvL

Wki

vvVvL

Wki

tGD

ttGS

tGSDStGD

ttGS

Vv

VVVv

VvvVv

VVVv

7.0~5.0,

region Saturation

or, ,

7.0~5.0,

:region Triode

6.3 IC BiasingThe Basic MOSFET Current Source

2

1

'1 2

1tnGSnD VV

L

WkI

R

VVII GSDDREFD

1

2

2

'2 2

1tnGSnDO VV

L

WkII

1

2

)/(

)/(

LW

LW

I

I

REF

O

SATURATION

6.3 IC BiasingThe Basic MOSFET Current Source (cont.)

tGSO VVV

Effect of Vo on Io

Effect of Channel Length Modulation

21

2 1A

GSOREFO V

VVI

LW

LWI

Output Resistance

O

A

O

OO I

V

I

VR 2

VA2: Early Voltage Channel Length

6.3 IC BiasingMOS Current-Steering Circuits

1

22 LW

LWII REF

1

33 LW

LWII REF

4

545 LW

LWII

tnGSSSDD VVVVV 132 ,

Effect of Vo on Io

Difference Q2 and Q5

Current Source, Current Sink

6.3 IC BiasingBJT Circuits

Current Transfer Ratio

mQ

Q

I

I

C

O 1

2

of EBJ of Area

of EBJ of Area

Case 1: m = 1

2

1

1

21

C

C

REF

O

I

I

I

I

C

CREF

III 2

Case 2:

1

1

mm

I

I

REF

O

Output Resistance

O

A

O

OO I

V

I

VR 2

2

11

1 A

BEOREFO V

VVmm

II

6.3 IC BiasingBJT Circuits – Current Steering

Effect of Vo on Io

R

VVVVI BEEBEECCREF

21

REFII 23

REFII 34

VVV CC 3.0collector

6.3 IC Biasing6.3.3 BJT Circuits: A Simple Current Source

R

VVI BECCREF

2

1/21 A

BEOREFO V

VVII

REF

AO I

VR

6.4 High-Frequency Response 6.4.1 The High-Frequency Gain Function

)()( sFAsA HM

gain DCor frequency -low gain, midband :MA

PnPP

ZnZZH sss

ssssF

/1/1/1

/1/1/1)(

21

21

S 0, F(s) 1

6.4 High-Frequency Response 6.4.2 Determining the 3-dB Frequency fH

121

21

/1

1

/1/1/1

/1/1/1)(

PPnPP

ZnZZH ssss

ssssF

A dominant pole exits if the lowest frequency pole is at least two octaves (a facotr of 4) away from the nearest pole or zero.

1PH

6.4 High-Frequency Response 6.4.2 Determining the 3-dB Frequency fH (cont.)

21

21

/1/1

/1/1)(

PP

ZZH ss

sssF

2222

22222

21

21

/1/1

/1/1)(

PP

ZZjFH

2222

2222

21

21

/1/1

/1/1

2

1

PP

ZZ

HH

HH

22

21

2

22

21

2

22

21

42

221

2

22

21

42

22

1

2

111

111

/11

1

/11

1

PPH

ZZH

PPHPP

H

ZZHZZ

H

22

21

22

21

22111

ZZPPH

6.4 High-Frequency Response 6.4.2 Determining the 3-dB Frequency fH (cont.)

44

5

104/110/1

10/1)(

ss

ssFH

Homework

5.77, 5.112, 4.11, 4.45, 4.74