Young Won Lim07/14/2017

BJT Topologies – Basic Bias

Young Won Lim07/14/2017

Copyright (c) 2012 – 2017 Young W. Lim.

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BJT Topologies – Basic Bias 3 Young Won Lim

07/14/2017

BJT Amplifier Topologies

n p nE

B

C

Common Base

n p n

B

Common Base

E

B

C

Common Emitter

n

p

n

E

BC

Common Emitter

n

p

n

E

B

C

Common Collector

n

p

n

E

B

C

Common Collector

n

p

n

E C

BJT Topologies – Basic Bias 4 Young Won Lim

07/14/2017

Common Base Topology

n p n

E

B

C

Current Flow

Common Base

n p n

E C

B

Current Flow

Common Base

IN OUT IN OUT

BJT Topologies – Basic Bias 5 Young Won Lim

07/14/2017

Common Emitter Topology

E

B

C

Current Flow

Common Emitter

n

p

n E

B

C

Current Flow

Common Emitter

n

p

n

IN

OUT

IN

OUT

BJT Topologies – Basic Bias 6 Young Won Lim

07/14/2017

Common Collector Topology

E

B

C

Current Flow

Common Collector

n

p

n

E

B

C

Current Flow

Common Collector

n

p

n

IN

OUT

IN

OUT

BJT Topologies – Basic Bias 7 Young Won Lim

07/14/2017

Forward bias (BE) & Reverse bias (CB)

E

B

C E

B

C

n

p

n

n

p

n

Common CollectorCommon EmitterCommon Base

n p n

E C

B

n

p

n

E

B

C

n

p

n

E

B

C

V BE

V CB

forward biasreverse bias

V BE

V CB

forward biasreverse bias

V BE

V CB

forward biasreverse bias

n p n

B

E C

BJT Topologies – Basic Bias 8 Young Won Lim

07/14/2017

Bias for the Active Region

+

–

+

–

+

–

BJT Topologies – Basic Bias 9 Young Won Lim

07/14/2017

B2B Diodes

Common CollectorCommon EmitterCommon Base

n p n

E C

B

n

p

n

E

B

C

n

p

n

E

B

C

V BE

V CB

forward bias

reverse bias

V BE

V CB

forward bias

reverse bias

V BE

V CB

forward bias

reverse bias

Active region Active region Active region

Active Region

BJT Topologies – Basic Bias 10 Young Won Lim

07/14/2017

Biasing B2B Diodes

Common CollectorCommon EmitterCommon Base

n p n

E C

B

n

p

n

E

B

C

n

p

n

E

B

C

V BE

V CB

forward bias

reverse bias

V BE

V CB

forward bias

reverse bias

V BE

V CB

forward bias

reverse bias

++ – –

+

+–

– +

+–

–

Active region Active region Active region

Active Region

BJT Topologies – Basic Bias 11 Young Won Lim

07/14/2017

+ +

Polarities of Two voltage supplies

E

B

C E

B

C

n

p

n

n

p

n

Common CollectorCommon EmitterCommon Base

V BE V CBV BE

V CBV BE

n p n

B

E C

Active Region

V CBE

B

C E

B

C

+

+

–

–

+

–

+

– +

–

–

+

–

–

V BE

V CB

forward bias

reverse bias

V BE

V CB

forward bias

reverse bias

V BE

V CB

forward bias

reverse bias

Active region Active region Active region

BJT Topologies – Basic Bias 12 Young Won Lim

07/14/2017

Two voltage supplies Bias

E

B

C E

B

C

n

p

n

n

p

n

Common CollectorCommon EmitterCommon Base

V BE

V CB

forward biasreverse bias

V BE

V CB

forward biasreverse bias

V BE

V CB

forward biasreverse bias

V BE V CB V BE V CE V CB V CE

n p n

B

E C

Active Region

Active region Active region Active region

BJT Topologies – Basic Bias 13 Young Won Lim

07/14/2017

Controlling VBE

& VCB

E

B

C E

B

C

n

p

n

n

p

n

Common CollectorCommon EmitterCommon Base

V BE

V CB

V BE

V CE

V CB

V CE

n p n

B

E C

Voltage of B from E

Voltage of C from B

Voltage of B from E

Voltage of C from E

Voltage of Cfrom B

Voltage of C from E

V CB + V BE V CB + V BE

+

–

–

+

–

+

–

+

–

+

–

+

Active Region

Direct Control Indirect Control Indirect Control

BJT Topologies – Basic Bias 14 Young Won Lim

07/14/2017

Slope Controlling Resistors Active Region

Input Characteristics Output Characteristics

BJT Topologies – Basic Bias 15 Young Won Lim

07/14/2017

Two Voltage Sources

n p n

B E

B

C E

B

C

n

p

n

n

p

n

++

+

+

+

+

– –

–

–

– – V BE V CB

V BE V CE V CB V CE

n p n

n

p

n

n

p

n

E C

V CB V BE

E B C

C

B

E

E

B

C

Common CollectorCommon EmitterCommon Base

Active Region

Active region Active region Active region

BJT Topologies – Basic Bias 16 Young Won Lim

07/14/2017

CE & CC Comparison

E

B

C E

B

C

n

p

n

n

p

n

+

+

+

+

– –

–

–

V BE V CE V CB V CE

n

p

n

n

p

n

V CB V BEC

B

E

E

B

C

Common Collector 2Common Emitter

E

B

C

n

p

n

++

–

–

V CB V CE

n

p

n

V BEE

B

C

Common Collector

Active Region

Active region Active region Active region

BJT Topologies – Basic Bias 17 Young Won Lim

07/14/2017

Bias for the Saturation Region

+

–

+

–

+

–

BJT Topologies – Basic Bias 18 Young Won Lim

07/14/2017

Large IC & Small V

CE

Input Characteristics Output Characteristicsac

tive

satu

rati

on

Large VBB

Large Ic

Large Voltage Drop across R

Small VCE

Saturated Current I

C

Saturation Region

BJT Topologies – Basic Bias 19 Young Won Lim

07/14/2017

B2B Diodes

Common CollectorCommon EmitterCommon Base

n p n

E C

B

n

p

n

E

B

C

n

p

n

E

B

C

V BE

V BC

forward bias V BE

V BC

forward bias V BE

V BC

forward bias

++ – –

++

–

– ++

–

–

forward bias forward bias forward bias

saturation saturation saturation

V BE V BC

V BE

V BC V BE

V BC

Saturation Region

BJT Topologies – Basic Bias 20 Young Won Lim

07/14/2017

Voltage Supply Polarities

E

B

C E

B

C

n

p

n

n

p

n

Common CollectorCommon EmitterCommon Base

V BE forward bias V BE forward bias V BE forward bias

n p n

B

E C

V BC V BC V BCforward bias forward bias forward bias

saturation saturation saturation

+

+

++

–

–

– –

+

–

+

–

Saturation Region

+

–

+– V BE V BC

V BE

V BCV BE

V BC

E

B

CE

B

C

smal

lV

CE

small

VCE

BJT Topologies – Basic Bias 21 Young Won Lim

07/14/2017

Two Voltage Sources

n p n

B E

B

C E

B

C

n

p

n

n

p

n

++

+

+

++

–

–

– –

– –

V BE V BC

V BE V CE V BC V CE

n p n

n

p

n

n

p

n

E C

V BC V BE

E B C

C

B

E

E

B

C

Common CollectorCommon EmitterCommon Base

saturation saturation saturation

+

–

+

–

Saturation Region

BJT Topologies – Basic Bias 22 Young Won Lim

07/14/2017

CE & CC Comparison

E

B

C E

B

C

n

p

n

n

p

n

Common CollectorCommon Emitter

saturation saturation

E

B

C

n

p

n

Common Collector 2

saturation

Saturation Region

+

+

++

–

–

– –

V BE V CE V BC V CE

n

p

n

n

p

n

V BC V BE

C

B

E

E

B

C

+

–

+

– +

+

–

–

V BC V CE

n

p

n

V BE

E

B

C

+

–

BJT Topologies – Basic Bias 23 Young Won Lim

07/14/2017

BJT Topologies – Basic Bias 24 Young Won Lim

07/14/2017

Active and Saturation Regions (1)

Common CollectorCommon EmitterCommon Base

saturation saturation saturation

active active active

Large VBB

, Small VCE

Large VBB

, Small VCE

Large VBB

, Small VCE

n p n

B E

B

C E

B

C

n

p

n

n

p

n

E C

n p n

B E

B

C E

B

C

n

p

n

n

p

n

E C

BJT Topologies – Basic Bias 25 Young Won Lim

07/14/2017

Active and Saturation Regions (2)

Common CollectorCommon EmitterCommon Base

saturation saturation saturation

++

+

+

+

+

– –

–

–

– – V BE V CB

V BE V CE V CB V CE

n p n

n

p

n

n

p

n

V CB V BE

E B C

C

B

E

E

B

C

active active active

++

+

+

++

–

–

– –

– –

V BE V BC

V BE V CE V BC V CE

n p n

n

p

n

n

p

n

V BC V BE

E B C

C

B

E

E

B

C

+

–

+

–

BJT Topologies – Basic Bias 26 Young Won Lim

07/14/2017

Active and Saturation Regions (3)

Common CollectorCommon Emitter

saturation saturation saturation

active active

Common Collector 2

E

B

C E

B

C

n

p

n

n

p

n

E

B

C

n

p

n

E

B

C E

B

C

n

p

n

n

p

n

E

B

C

n

p

n

active

BJT Topologies – Basic Bias 27 Young Won Lim

07/14/2017

Active and Saturation Regions (4)

Common CollectorCommon Emitter

saturation saturation

active active

saturation

active

Common Collector 2

+

+

++

–

–

– –

V BE V CE V BC V CE

n

p

n

n

p

n

V BC V BE

C

B

E

E

B

C

+

–

+

– +

+

–

–

V BC V CE

n

p

n

V BE

E

B

C

+

–

+

+

+

+

– –

–

–

V BE V CE V CB V CE

n

p

n

n

p

n

V CB V BEC

B

E

E

B

C ++

–

–

V CB V CE

n

p

n

V BEE

B

C

BJT Topologies – Basic Bias 28 Young Won Lim

07/14/2017

BJT Topologies – Basic Bias 29 Young Won Lim

07/14/2017

Common Base (1)

n p n

E

B

C

Common Base

n p n

E

B

C

Electron Flow Current Flow

Common Base

forward bias reverse bias forward bias reverse bias

BJT Topologies – Basic Bias 30 Young Won Lim

07/14/2017

Common Base (2)

n p n

E

B

C

Electron Flow

n p n

E C

n p n n p n

B

E

B

C E C

B

Current Flow

Common Base Common Base

BJT Topologies – Basic Bias 31 Young Won Lim

07/14/2017

Common Emitter (1)

E

B

C

E

B

C

Electron Flow Current Flow

Common Emitter Common Emitter

n

p

n

n

p

nforward bias

reverse bias

forward bias

reverse bias

BJT Topologies – Basic Bias 32 Young Won Lim

07/14/2017

Common Emitter (2)

E

B

C

E

B

C

Electron Flow Current Flow

Common Emitter Common Emitter

n

p

n

n

p

n

n

p

n

n

p

n

BJT Topologies – Basic Bias 33 Young Won Lim

07/14/2017

Common Collector (1)

E

B

C

E

B

C

Electron Flow Current Flow

Common Collector Common Collector

n

p

n

n

p

n

forward bias

reverse bias

forward bias

reverse bias

BJT Topologies – Basic Bias 34 Young Won Lim

07/14/2017

Common Collector (2)

E

B

C

E

B

C

Electron Flow Current Flow

Common Collector Common Collector

n

p

n

n

p

n

n

p

n

n

p

n

BJT Topologies – Basic Bias 35 Young Won Lim

07/14/2017

BJT Bias

n p nE C

n p n

B E

B

C E

B

C

n

p

n

n

p

n

n

p

n

n

p

n

E

B

C E

B

C

E C

B

++

+

+

+

+

– –

–

–

– –

Common CollectorCommon EmitterCommon Base

V BE V CB

V BE V CE V CB V CE

BJT Topologies – Basic Bias 36 Young Won Lim

07/14/2017

Common Emitter (2)

Electron Flow

n p n

E C

Current Flow

n p n n p n

B

Young Won Lim07/14/2017

References

[1] http://en.wikipedia.org/[2] J.H. McClellan, et al., Signal Processing First, Pearson Prentice Hall, 2003