Young Won Lim05/26/2017

BJT Bias

Young Won Lim05/26/2017

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

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BJT Bias 3 Young Won Lim05/26/2017

BJT 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

BJT Bias 4 Young Won Lim05/26/2017

Common Base

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 Bias 5 Young Won Lim05/26/2017

Common Emitter

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 Bias 6 Young Won Lim05/26/2017

Common Collector

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 Bias 7 Young Won Lim05/26/2017

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 Bias 8 Young Won Lim05/26/2017

Biasing Back-to-back 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 biasreverse bias

V BE

V CB

forward biasreverse bias

V BE

V CB

forward biasreverse bias

++ – –

+

+–

–

+

+–

–

BJT Bias 9 Young Won Lim05/26/2017

Two voltage supplies

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

BJT Bias 10 Young Won Lim05/26/2017

Two voltage supplies controls 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 C from B

Voltage of C from E

V CB + V BE V CB + V BE

+

–

–

+

–

+

–

+

–

+

–

+

BJT Bias 11 Young Won Lim05/26/2017

Two voltage supplies with resistors

n p n

B 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

n

p

n

n

p

n

E C

V CB V BE

E B C

C

B

E

E

B

C

BJT Bias 12 Young Won Lim05/26/2017

BJT Bias 13 Young Won Lim05/26/2017

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 Bias 14 Young Won Lim05/26/2017

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 Bias 15 Young Won Lim05/26/2017

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 Bias 16 Young Won Lim05/26/2017

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 Bias 17 Young Won Lim05/26/2017

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 Bias 18 Young Won Lim05/26/2017

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 Bias 19 Young Won Lim05/26/2017

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 Bias 20 Young Won Lim05/26/2017

Common Emitter (2)

Electron Flow

n p n

E C

Current Flow

n p n n p n

B

BJT Bias 21 Young Won Lim05/26/2017

Maintain Magnetic Field

Before Initial Final

No Energy in magnetic field

+

−

Induced EMF

BJT Bias 22 Young Won Lim05/26/2017

Storing Magnetic Energy

v vR

vL

i iR

iL

= +

= =

Young Won Lim05/26/2017

References

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