BJT Topologies – AC Characteristics · PDF fileZ CB : low CE : high CC : high in ... BJT...

Young Won Lim08/04/2017

BJT Topologies – AC Characteristics


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

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BJT Topologies – AC Characteristics 3 Young Won Lim

08/04/2017

Input Characteristic CurvesOutput Characteristic Curves


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CE Amplifier : Linear Region

E

B

Cn

p

n

+

+

– –

V BE V CE

n

p

n

V CBC

B

E

Common Emitter

Active region

V BE V CE

V CB

V BBV RB

V RC V CC

Input Characteristics Output Characteristics

0.7V

BJT Topologies – DC Characteristics 5 Young Won Lim

08/04/2017

CE Amplifier : Saturation Region

E

B

Cn

p

n

Common Emitter

V BBV RB

V RC V CCsaturation

+

+

– –

V BE V CE

n

p

n

V BC

C

B

E

+

–

V BE V CE

V BC

0.7V


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CC Amplifier : Characteristic Curves


Common Collector 3

Active region

E

B

C n

p

n

+

+

– –

V BE V CE

n

p

n

V CBC

B

E

V BC V EC

V BC

V BE−V CE

V EC

−V CE


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CB Amplifier : Characteristic Curves


Active region

Common Base

n p n

B

E C

+

+

– –

V BE V CE

n

p

n

V CBC

B

E

V EB V EB

IE

V CB

IC

V CE−V BE


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Vin & V

out Phase Relationship


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Notations

V CE

vce = vce(t)

ac instantaneous

V ce

ac rmsac avgac p-to-p

DC AC DC + AC

V CE + v ce

UPUPlowlow

UPlow


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CE Amplifier : Phase Relationship

E

B

Cn

p

n

Common Emitter

vs( t) vs( t)

vs

V BB

V BB

vs + V BB

Input Characteristics

V BB V BB

+V s

V BB

−V s

inc IB+ I b → inc IC+ I c , I E+ I e

dec IB− I b → dec IC−I c , IE− I e


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CE Amplifier : Phase Relationship

E

B

Cn

p

n

Common Emitter Input Characteristics Output Characteristics

increasing vi direction

decreasing vo direction

Active region


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CC Amplifier : Phase Relationship

Input Characteristics Output CharacteristicsCommon Collector 3

Active region

E

B

C n

p

n

V BC

V BE−V CE

V EC

−V CE


increasing vo direction


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CB Amplifier : Phase Relationship


Active region

Common Base

n p n

B

E C

V EB

IE

V CB

IC

V CE−V BE


increasing vo direction


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DC bias only circuitsDC + small AC AC only circuits


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BJT Amplifier Configurations

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


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Basic BJT Configuration Circuits

B

Common Base

E

BC

Common Emitter

E

B

C

Common Collector

E C

BE

BC E

B

C

E C−V EE −V CC

V CC

V BB −V BB

−V CC


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DC Bias

B

Common Base

E

BC

Common Emitter

E

B

C

Common Collector

E C


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DC Bias + AC Small Signal

B

Common Base

E

BC

Common Emitter

E

B

C

Common Collector

E C


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AC Equivalent Circuits

B

Common Base

E

BC

Common Emitter

E

B

C

Common Collector

E C

B

E C

vo

E

B

C

vo

E

BC

vo


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CB Amplifiers – DC Bias, AC Signal, Output LoadCE Amplifiers – DC Bias, AC Signal, Output LoadCC Amplifiers – DC Bias, AC Signal, Output Load


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Common Base

B

E C

B

E C

B

E C

DC Bias DC Bias + AC Signal

AC Signal AC Signal + Load

B

E C

DC Bias + AC Signal + Load

B

E C

vo

vo

vo


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Common Emitter

E

BC

E

BC

E

BC

E

BC

E

BC

DC Bias DC Bias + AC Signal DC Bias + AC Signal + Load


vo

vo

vo


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Common Collector

E

B

C

E

B

C

E

B

C

E

B

C

E

B

C

DC Bias DC Bias + AC Signal DC Bias + AC Signal + Load


vo

vo

vo


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AC Equivalent ModelT-modelPi-model

Input ImpedanceOutput Impedance Voltage Gain Current Gain


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AC t & pi models

B

Common Base

E

B

C

Common Emitter

E

B

C

Common Collector

E C

B

Common Base

E

B

C

Common Emitter

E

B

C

Common Collector

E C


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Input Impedance Zin

Zin : low

Ie

: Large

Zin

: high

Ib

: Small

Zin

: high

Ib : Small

E

B

C

Common Base

E

B

C

Common Emitter

E

B

C

Common Collector

re ' β re ' β(re '+RE)

I e Ib Ib


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Output Impedance Zin

Zout

: high

Thevenin R

Zout

: high

Thevenin R

Zout

: low

Thevenin R

E

B

C

Common Base

E

B

C

Common Emitter

E

B

C

Common Collector

RC RC re '


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Voltage Gain Av

Common Base Common Emitter Common Collector

Av : high A

v : high A

v: unityRC /re ' RC /re ' 1

I e I c I e

I c

I e

I e


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Current Gain Ai


I e I c

I c

IbIb

I c

Ai : unity A

i: high A

i: high1 β β


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BJT Configuration Properties


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BJT Configuration Properties (1)

input Z : lowoutput Z : highvoltage gain : highcurrent gain : unity

input Z : highoutput Z : highvoltage gain : highcurrent gain : high

input Z : highoutput Z : lowvoltage gain : unitycurrent gain : high

BCCB CE EC

BEEB

n p nE

B

C

Common Base

E

B

C

Common Emitter

n

p

n

E

B

C

Common Collector

n

p

n

RF Applications Widely used Emitter FollowerBuffer to Low Impedance Load

Low Zin

Low Zout


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BJT Configuration Properties (2)

Zin : low

Zout

: high

Av : high

Ai : unity

Zin

: high

Zout

: high

Av

: high

Ai

: high

Zin

: high

Zout

: low

Av

: unity

Ai

: high

n p nE

B

C

Common Base

E

B

C

Common Emitter

n

p

n

E

B

C

Common Collector

n

p

n

re '

RC

RC /re '

1

β re '

RC

RC /re '

β

β(re '+RE)

re '

1

β


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re '

RC

β re '

RC

β

β(re '+RE)

re '

1

CB : low CE : high CC : highZin

CC : lowZout CE : high CB : high

CC : unity CB : highCE : high RC /re ' RC /re '

CB : unity CE : high CC : high

Av

Ai 1 β

CB : low

CB : high

CB : high

CB : unity

CE : high

CE : high

CE : high

CE : high

CC : high

CC : low

CC : unity

CC : high

re '

RC

RC /re '

1

β re '

RC

RC /re '

β

β(re '+r E)

re '

1

β

Zin

Zout

Av

Ai



08/04/2017


CB : low

CB : high

CB : high

CB : unity

CE : high

CE : high

CE : high

CE : high

CC : high

CC : low

CC : unity

CC : high

re '

RC

RC /re '

1

β re '

RC

RC /re '

β

β(re '+r E)

re '

1

β

Zin

Zout

Av

Ai


CB : low

CB : high

CB : high

CB : unity

CE : med

CE : med

CE : med

CE : med

CC : high

CC : low

CC : unity

CC : high

r e

RC

α RC

(R s+r e)

α

r π=(β+1)r e

RC ∣∣ r o

β(RC ∣∣ r0)

(R s+rπ)

β ro

(R c+r o)

(β+1)[re+(ro∣∣RL)]

r o ∣∣[re+R s

(β+1) ]

(b+1)(RL ∣∣r o)

R s+(β+1)[ re+(RL∣∣r o)]

(β+1)r o

r o+RL

Zin

Zout

Av

Ai


ro , Rs , RE are used


08/04/2017


CB : low

CB : high

CB : high

CB : unity

CE : high

CE : high

CE : high

CE : high

CC : high

CC : low

CC : unity

CC : high

re '

RC

RC /re '

1

β re '

RC

RC /re '

β

β(re '+r E)

re '

1

β

Zin

Zout

Av

Ai


CB : low

CB : high

CB : high

CB : unity

CE : med

CE : med

CE : med

CE : med

CC : high

CC : low

CC : unity

CC : high

r e∣∣ RE ≈ r e

RC

RC

r e, RC ∣∣ RL

r e

R1 ∣∣ R2 ∣∣β re

RC (r e+Rs

β )∣∣RE =Rs

β ∣∣RE

RE

(re+RE )≈ 1

Zin

Zout

Av

Ai


VDB

RC

r e, RC ∣∣ RL

r e

R1 ∣∣ R2 ∣∣β(r e+RE)


08/04/2017

AC Equivalent Circuits

Input Characteristic CurvesOutput Characteristic Curves


08/04/2017

Storing Magnetic Energy

v vR

vL

i iR

iL

= +

= =


References

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

BJT Topologies – AC Characteristics · PDF fileZ CB : low CE : high CC : high in ... BJT...

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