Lecture 27 Bipolar Junction Transistors

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Lecture 27Bipolar Junction Transistors
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Bipolar Junction Transistors
1. Understand bipolar junction transistor
operation in amplifier circuits. 2. Analyze
simple amplifiers using the load-line technique
and understand the causes of nonlinear distortion.
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Tubes
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Deforests Audion
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Triode Tube
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Bardeen, Brittain and Shockley
Discovery of the transistor in 1947
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First Transistor
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Initial Demonstration of Solid State Amplification
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(No Transcript)
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First Integrated Circuit (IC)
Jack Kilby at Texas Instruments (1958)
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Early Integrated Circuit (IC)
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Chip Evolution
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NPN and PNP Bipolar Junction Transistors (BJT)
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r/bipolar_transistor.htm
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NPN Bipolar Junction Transistor
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Bias Conditions for PN Junctions
The base emitter p-n junction of an npn
transistor is normally forward biased
The base collector p-n junction of an npn
transistor is normally reverse biased
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Bias Conditions for NPN Junctions
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r/bipolar_transistor.htm
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Bias Conditions for NPN Junctions
http//www.mtmi.vu.lt/pfk/funkc_dariniai/transisto
r/bipolar_transistor.htm
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Bias Conditions for NPN Junctions
http//www.mtmi.vu.lt/pfk/funkc_dariniai/transisto
r/bipolar_transistor.htm
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Bias Conditions for NPN Junctions
http//www.mtmi.vu.lt/pfk/funkc_dariniai/transisto
r/bipolar_transistor.htm
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Equations of Operation
From Kirchoffs current law
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Equations of Operation
Define ? as the ratio of collector current to
emitter current
Values for ? range from 0.9 to 0.999 with 0.99
being typical. Since
Most of the emitter current comes from the
collector and very little (?1) from the base.
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Equations of Operation
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Equations of Operation
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Equations of Operation
Define ?? as the ratio of collector current to
base current
Values for ? range from about 10 to 1,000 with a
common value being ? ? 100.
The collector current is an amplified version of
the base current.
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Equations of Operation
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The base region is very thin
Only a small fraction of the emitter current
flows into the base provided that the
collector-base junction is reverse biased and the
base-emitter junction is forward biased.
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Exercise 13.1
A certain transistor has ? 50, IES 10-14A,
vCE 5 V, and iE 10 mA. Assume VT 0.026 V.
Find vBE, vBC, iB, iC and ?.
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Exercise 13.2
Compute the corresponding values of ? if ? 0.9,
0.99 and 0.999
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Exercise 13.3
A certain transistor operated with forward bias
of the base-emitter junction and reverse bias of
the base-collector junction has iC 9.5 mA and
iE 10 mA. Find the value of iB, ? and ?.
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Common-Emitter Characteristics
vBC
vCE
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Common-Emitter Input Characteristics
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Common-Emitter Output Characteristics
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Amplification by the BJT
A small change in vBE results in a large change
in iB if the base emitter is forward biased.
Provided vCE is more than a few tenths of a
volt, this change in iB results in a larger
change in iC since iC?iB.
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Common-Emitter Amplifier
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Load-Line Analysis of a Common Emitter Amplifier
(Input Circuit)
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Load-Line Analysis of a Common Emitter Amplifier
(Output Circuit)
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Inverting Amplifier
As vin(t) goes positive, the load line moves
upward and to the right, and the value of iB
increases. This causes the operating point on
the output to move upwards, decreasing vCE ? An
increase in vin(t) results in a much larger
decrease in vCE so that the common emitter
amplifier is an inverting amplifier
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Load-Line Analysis of BJT
Assume VCC 10V VBB 1.6V RB 40 k? RC 2
k? Vin 0.4sin(?t)
iBQ 25 ?A
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Load-Line Analysis of BJT
Assume VCC 10V VBB 1.6V RB 40 k? RC 2
k? Vin 0.4sin(?t)
iBmax 35 ?A
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Load-Line Analysis of BJT
Assume VCC 10V VBB 1.6V RB 40 k? RC 2
k? Vin 0.4sin(?t)
iBmin 15 ?A
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Load-Line Analysis of BJT
iBQ 25 ?A iBmin 15 ?A iBmax 35 ?A
VCEQ 5V iCEQ 2.5 mA
VCEQ 5V VCEmin 3V VCEmax 7V
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Load-Line Analysis of BJT
Voltage waveforms for the common emitter
amplifier. The gain is -5 (inverting).
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Clipping
When iC becomes zero, we say that the transistor
is cutoff. When vCE ? 0.2 V, we say that the
transistor is in saturation.
Amplification occurs in the active region.
Clipping occurs in the saturation or cutoff
regions.
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Clipping
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Exercise 13.5
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Exercise 13.5
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Exercise 13.5
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Exercise 13.5
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Exercise 13.6
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Exercise 13.6
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Exercise 13.6
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Exercise 13.6
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PNP Bipolar Junction Transistor
Except for reversal of current directions and
voltage polarities, the pnp BJT is almost
identical to the npn BJT.
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PNP Bipolar Junction Transistor
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Common-Emitter Characteristics for a PNP BJT
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Exercise 13.7
Find ?
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Exercise 13.8
Common emitter amplifier
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Exercise 13.8
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Exercise 13.8
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Exercise 13.8
Common emitter amplifier
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Exercise 13.8
Load line
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Exercise 13.8