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1 www.ice77.net Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals are called collector (C), base (B) and emitter (E). The BJT is a current-controlled device and it behaves like a switch. Its on state depends on a specific amount of voltage necessary to turn the device on: this threshold voltage is called V BE(ON) or V EB(ON) and it’s about 0.3V for germanium transistors or 0.7V for silicon transistors. BJTs come in two types: NPN and PNP. Under normal operating conditions, in NPN transistors the BE junction is forward-biased while the BC junction is reverse-biased. Similarly, in PNP transistors the EB junction is forward-biased while the CB junction is reverse-biased. V 0 I V 0 V1 0Vdc 0 Q1 Q2N2222 I1 0Adc I NPN BJT (Q2N2222) The transistor is off until V BE reaches about 0.6V. Then the transistor turns on and there are two possibilities: if V CE is less than 0.2V the transistor is in the saturation region whereas if V CE is more than 0.2V the transistor is in the active/linear region. In the active/linear region the collector current stays fairly constant and that is where the transistor typically operates.

Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

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Page 1: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

1 www.ice77.net

Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals are called collector (C), base (B) and emitter (E). The BJT is a current-controlled device and it behaves like a switch. Its on state depends on a specific amount of voltage necessary to turn the device on: this threshold voltage is called VBE(ON) or VEB(ON) and it’s about 0.3V for germanium transistors or 0.7V for silicon transistors. BJTs come in two types: NPN and PNP. Under normal operating conditions, in NPN transistors the BE junction is forward-biased while the BC junction is reverse-biased. Similarly, in PNP transistors the EB junction is forward-biased while the CB junction is reverse-biased.

V

0

I

V

0

V1

0Vdc

0

Q1

Q2N2222

I1

0Adc

I

NPN BJT (Q2N2222) The transistor is off until VBE reaches about 0.6V. Then the transistor turns on and there are two possibilities: if VCE is less than 0.2V the transistor is in the saturation region whereas if VCE is more than 0.2V the transistor is in the active/linear region. In the active/linear region the collector current stays fairly constant and that is where the transistor typically operates.

Page 2: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

2 www.ice77.net

DC sweep (IC/VCE)

The IC/VCE characteristics are plotted above (IC is on the Y axis and VCE is on the X axis). The graph is a DC sweep generated by a primary DC voltage source (0V to 10V) and a secondary DC current source (10µA to 100µA). The sweep shows 10 different collector currents (all in red), each one of them generated by a specific base current (increments of 10µA). At the bottom, a 10µA base current produces a 1.5mA collector current in the active/linear region.

V _ V 1

0 V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8 V 9 V 1 0 VV ( I 1 : - )

5 5 0 m V

6 0 0 m V

6 5 0 m V

7 0 0 m V

7 5 0 m V

DC sweep (VBE/VCE)

The VBE/VCE characteristics are shown above (VBE is on the Y axis and VCE is on the X axis). The graph is a DC sweep generated by a primary DC voltage source (0V to 10V) and a secondary DC current source (10µA to 100µA). The sweep shows 10 different voltages across the BE junction (all in green), each one of them generated by a specific base current (increments of 10µA). At the bottom, a 10µA base current sets the voltage of the BE junction to 657mV in the active/linear region.

V_V1

0V 1V 2V 3V 4V 5V 6V 7V 8V 9V 10VIC(Q1)

0A

5mA

10mA

15mA

20mA

active/linear

saturation

Page 3: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

3 www.ice77.net

BJT characteristics

N

C

Q1

Q2N2222

IeP

IbP

BNP

C

N

E

Ie

Ib

Q2

Q2N2906

Ic

Ic

E

PNP

B

NPN

CURRENT-VOLTAGE CHARACTERISTICS IN THE ACTIVE/LINEAR REGION DC parameters

A

CEnV

V

SC V

VeII T

BE

1

A

ECnV

V

SC V

VeII T

EB

1 BCE III

BE II )1(

1B

C

I

I (50<β<300)

EBC III 1

E

C

I

I (0.980<α<0.997)

S

CTBE I

InVV ln

AC parameters

C

A

C

CEAo I

V

I

VVr

eT

Cm rrV

Ig

mC

T

E

Te gI

V

I

Vr

emC

T

B

T rgI

V

I

Vr 1

PARAMETRIC SWEEP FOR THE COMMON EMITTER CONFIGURATION

I

0

V1

0Vdc

I

0

0

Q1

Q2N2222

I1

0Adc

V_V1

0V 1V 2V 3V 4V 5V 6V 7V 8V 9V 10VIC(Q1)

0A

5mA

10mA

15mA

20mA

active/linear

saturation

VBE=0.7V VEB=0.7V

NPN PNP

VCE(min)=0.2V VBC(max)=0.5V

+VBE-

+VCE-

-VEB+

+VEC-

TRANSCONDUCTANCE

EARLY EFFECT

Page 4: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

4 www.ice77.net

Facts about BJTs

1. The BJT was invented in 1947 by Bardeen, Brattain and Shockley.

2. Early BJTs were made of germanium (Ge). Modern BJTs are made of silicon (Si).

3. An NPN transistor has an n-type collector, a p-type base and an n-type emitter.

Electrons are minority carriers in the base and they define the type of current in

the device.

4. In an NPN transistor, the emitter is heavily doped (n+) while the collector is lightly

doped (n).

5. BJTs are bipolar devices because their operation depends on electrons and

holes rather than either electrons or holes like in MOSFETs.

6. The emitter takes its name from the fact it is the emitter of charge carriers

(electrons for NPN and holes for PNP).

7. NPN transistors are more popular than PNP transistors because electron mobility

is higher than hole mobility in semiconductors. This translates into higher current

and faster operation.

8. BJTs, when compared to MOSFETs, have higher transconductance (gm) for

same output current (iC versus iD).

9. BJTs are preferred over MOSFETs for most analog applications.

10. BJTs and MOSFETs can be combined into BiCMOS to use advantages of both

technologies.

11. Heterojunction Bipolar Transistors (HBTs) are improved BJTs that can handle

high frequencies. They are made of silicon-germanium (Si-Ge) or aluminum

gallium arsenide (AlGaAs). Essentially, they are high-speed BJTs.

12. BJTs are preferred over MOSFETs for very high-frequency applications such as

radio-frequency circuits for wireless systems.

Page 5: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

5 www.ice77.net

Common Emitter Configuration

R1

90k

200.5uA

0V

V

11.30V

0

RC

10k

869.7uA

0

0V

0V

CB

10uFRL

20k0A

0

0

20.00V

CE

470uF

CC

10uF

REDC

1k

875.0uA

V

0V

Rs

500A

20.00V

Vs

FREQ = 1kHzVAMPL = 500mVVOFF = 0V

0A

VCC

Q1

Q2N2222

5.359uA869.7uA

-875.0uA

0

1.313V

R2

10k

195.2uA

1.952V

20.00V

REAC

500

875.0uA

0

VCC

VCC20Vdc

1.070mA

VCC

0V

Common Emitter Configuration

The Common Emitter Configuration features a grounded emitter. However, in the above schematic, two emitter resistors and a capacitor are also present. The components are introduced to ensure stability and avoid clipping of the output waveform. The load is connected to the collector.

Time

0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0msV(CC:2) V(Vs:+)

-8.0V

-4.0V

0V

4.0V

8.0V

Time domain sweep at 1kHz

The voltage gain is greater than 1 and the output is 180° out of phase with respect to the input.

Page 6: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

6 www.ice77.net

CE

470uF

V

20.00V

20.00V

0

1.313V

RL

20k0A

0

1.952V

R1

90k

200.5uA

Vs500mVac0Vdc

0A

VCC

0V

REAC

500

875.0uA

V

CB

10uF

VCC

0

20.00V

VCC20Vdc

1.070mA

0V

RC

10k

869.7uA

Q1

Q2N2222

5.359uA869.7uA

-875.0uA

R2

10k

195.2uA

0V

0V

CC

10uF

0

VCC

0

Rs

500A

0V

REDC

1k

875.0uA

0

11.30V

Common Emitter Configuration

Frequency

10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHzV(CC:2) V(Vs:+)

0V

2.0V

4.0V

6.0V

8.0V

AC sweep from 10mHz to 10GHz

The amplifier is linear from about 2.5Hz to 7.5MHz. The voltage gain in the midband is about 12. REAC increases input resistance and lowers the voltage gain but it can also distort the output. CE lowers the low –3dB frequency point.

Page 7: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

7 www.ice77.net

Common Collector Configuration

CE

10uF

R1

20k

169.0uA

V

0V

0V

R2

200k

83.10uA

VCC

0V

Vs

FREQ = 1kHzVAMPL = 500mVVOFF = 0V

0A

RL

20k0A

0

Q1

Q2N2222

85.86uA15.82mA

-15.90mA

0

20.00V

Rs

500A

V

CB

10uF

15.90V

VCC

20.00V

0

0

0V

15.90V

0V

RE

1k

15.90mA

0V

16.62V

20.00V

0

VCC

VCC20Vdc

15.99mA

Common Collector Configuration

The Common Collector Configuration features an AC grounded collector. The load is connected to the emitter.

Time

0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0msV(RL:2)

-500mV

0V

500mVV(Vs:+)

-500mV

0V

500mV

SEL>>

Time domain sweep at 1kHz

The voltage gain is close to 1 and the output is in phase with respect to the input.

Page 8: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

8 www.ice77.net

20.00V

0V

CE

10uF

R1

20k

169.0uA

V

0V

20.00V

0V

R2

200k

83.10uA

VCC

15.90V

RL

20k0A

15.90V

0

Q1

Q2N2222

85.86uA15.82mA

-15.90mA

0

20.00V

Rs

500A

Vs500mVac0Vdc

0A

V

CB

10uF

VCC

0

0V

0

16.62V

RE

1k

15.90mA 0V

0

0V

VCC

VCC20Vdc

15.99mA

Common Collector Configuration

Frequency

10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHz 1.0THzV(Vs:+) V(RL:2)

0V

100mV

200mV

300mV

400mV

500mV

AC sweep from 10mHz to 1THz

The amplifier is linear from about 1.4Hz to 587MHz. The voltage gain in the midband is almost 1. This amplifier is often called Emitter Follower.

Page 9: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

9 www.ice77.net

Common Base Configuration

V

CE

100uF

V+6Vdc

4.346mA

R1

60k

81.36uA

V+

Rs

50

0A

1.119V

V

V+

0

CB

100uF

V-

V

0

Q1

Q2N2222

25.43uA

4.265mA

-4.290mA

1.736V

0V

RE

1.5k

4.290mA

6.000V

RC

1k

4.265mA

0

V1

FREQ = 1kHzVAMPL = 50mVVOFF = 0V

0A

434.9mV0

0V

V+

0

0V

RL

20k0A

V-

0V

V--6Vdc

4.290mA

R2

20k

55.93uA

0V

-6.000V

CC

10uF

0V

Common Base Configuration

The Common Base Configuration features an AC grounded base. In the above schematic the two resistors at the base are used to bias the transistor. The load is connected to the collector and the voltage gain is the ratio of the voltage at the output over the voltage at the emitter.

Time

0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0msV(CC:2) V(V1:+) V(CE:1)

-1.0V

-0.5V

0V

0.5V

1.0V

Time domain sweep at 1kHz

The voltage gain is greater than 1 and the output is in phase with respect to the input.

Page 10: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

10 www.ice77.net

0VR2

20k

55.93uA

0

1.736V

RC

1k

4.265mA

R1

60k

81.36uA -6.000V

0V

0

0

V+

V+

CB

100uF

Q1

Q2N2222

25.43uA

4.265mA

-4.290mA

434.9mV0

V

0V

CE

100uF

6.000V

V+6Vdc

4.346mA

V+

V-

0V

V250mVac0Vdc

0A

V-

V

0V

RE

1.5k

4.290mA

V

Rs

50

0A

V--6Vdc

4.290mA

0V

1.119V

CC

10uF

0

RL

20k0A

Common Base Configuration

Frequency

10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHzV(RL:2) V(Rs:1) V(CE:1)

0V

0.5V

1.0V

AC sweep from 10mHz to 10GHz

The amplifier is linear from about 28.5Hz to 22.95MHz. The voltage gain in the midband is about 145 (VC/VE). The highest gain attainable by a BJT amplifier is provided by the Common Base Configuration. The highest bandwidth attainable by a BJT amplifier is provided by the Common Collector Configuration.

Page 11: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

11 www.ice77.net

Multistage BJT amplifier I

C4

10u

C2

10u

1.943V

1.039V

C3

10u

C5

10u

R4

10k

1.032mA

V2

20Vdc

3.699mA

0

VCC

R6

1k

1.039mA

R10

250

1.039mA

0R5

250

1.039mA

0

20.00V

V

20.00V

0V

1.039V

R13

10k

194.3uA

0

0V

1.943V

R15

250

1.039mA

R16

1k

1.039mA

R12

90k

200.6uAVCC

R11

1k

1.039mA

0

9.676V

R14

10k

1.032mA

VCC

R3

10k

194.3uA

0

R7

90k

200.6uA

C7

10u

RL

10k

0A

20.00V

0

0

20.00V

0V

1.299V

R1

500A

C1

10u

0V

V

0V

V1

FREQ = 1kHzVAMPL = 1mVVOFF = 0V

0A

R2

90k

200.6uA0

VCC

Q2

Q2N22226.367uA

1.032mA

-1.039mA

Q3

Q2N22226.367uA

1.032mA

-1.039mA

1.299V

R8

10k

194.3uA

Q1

Q2N22226.367uA

1.032mA

-1.039mA

9.676V

VCC

0

1.299V

0

VCC

C6

10u

1.943V

0

1.039V

R9

10k

1.032mA

VCC

0V

0V

Multistage BJT amplifier I

A sequence of Common Emitter amplifiers can be combined to produce higher gain but reduced bandwidth.

Time

0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0msV(RL:2)

-5.0V

0V

5.0VV(V1:+)

-1.0mV

0V

1.0mV

SEL>>

Time domain sweep at 1kHz

The voltage gain is about 4271 and the output is 180° out of phase with respect to the input.

Page 12: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

12 www.ice77.net

0

20.00V

1.943V

V

0

VCC

0V

1.039V

1.039V

VCC

R8

10k

194.3uA1.943V

20.00V

C3

10u

0

Q2

Q2N22226.367uA

1.032mA

-1.039mA

VCC

R13

10k

194.3uA

0

0

0

0V

20.00V

R5

250

1.039mA

1.039V0V

0

VCC

VCCV2

20Vdc

3.699mA 9.676V

0

0

R2

90k

200.6uA

R3

10k

194.3uA

R4

10k

1.032mA

R16

1k

1.039mA

9.676V

R9

10k

1.032mA

1.299V

0

1.299V

R6

1k

1.039mA

Q1

Q2N22226.367uA

1.032mA

-1.039mA

R14

10k

1.032mA

C7

10u

V

0V

C4

10u

R10

250

1.039mA

0

C2

10u

VCC

C6

10u

20.00V

1.299V

R15

250

1.039mA

R12

90k

200.6uA

R11

1k

1.039mA

R1

500A

C5

10u

Q3

Q2N22226.367uA

1.032mA

-1.039mA

V11mVac0Vdc

0A

VCC

0V

C1

10u

0V

R7

90k

200.6uA

0

1.943V

RL

10k

0A

0V

Multistage BJT amplifier I

Frequency

100mHz 1.0Hz 10Hz 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz 1.0GHzV(RL:2) V(R1:1)

0V

200mV

400mV

600mV

800mV

AC sweep from 100mHz to 1GHz

The amplifier is linear from 133Hz to 294kHz. The voltage gain in the midband is about 4271. The gain is high so the bandwidth is reduced.

Page 13: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

13 www.ice77.net

Multistage BJT amplifier II

0

Q2

Q2N222218.39uA

3.617mA

-3.636mA

V+

10.37V4.310V

R11

30k 503.5uAR7

50k

86.21uA

Rs

500A

V+

V+20Vdc

9.918mA

3.636V

0V

Q1

Q2N2222

17.42uA2.881mA

-2.898mA

C3

10uF

0

C2

10uF

5.598V

3.188V

0

0

V-

20Vdc

2.423mA

0V

0

V+

R1

40k

403.5uA

R3

5k

2.881mA

V+

020.00V

20.00V

R2

10k

386.1uAV1

FREQ = 1kHzVAMPL = 1mVVOFF = 0V

0A

R10

10k489.4uA

0

R4

100

2.898mA

00

4.227V

R9

10k

2.423mA

20.00V

0V

V+ V-

R12

4k

2.409mA

Q3 Q2N2222

14.13uA

2.409mA-2.423mA

V+

4.894V

R6

150k

104.6uA

3.861V

-20.00V

0

0V

C1

10uF

0V

C4 20uF

C5

10uF

C6

10uF

R8

1k

3.636mA

R5

1k

2.898mA0V

V

V+

2.898VV-

V

0

0V

RL

20k

0A

Multistage BJT amplifier II

The three configurations of the BJT can be combined in sequence. In the above schematic the amplifier has three stages: CE, CC and CB (left to right). The combination of these produces high gain and moderate bandwidth.

Time

0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0msV(C6:1)

-4.0V

0V

4.0VV(V1:+)

-1.0mV

0V

1.0mV

SEL>>

Time domain sweep at 1kHz

The voltage gain is about 3262 and the output is 180° out of phase with respect to the input.

Page 14: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

14 www.ice77.net

R1

40k

403.5uA

0

3.188V

V+20Vdc

9.918mA

4.894V

3.636V

R3

5k

2.881mA

C4 20uF

0

Q1

Q2N2222

17.42uA2.881mA

-2.898mA

0V

C5

10uF

4.227V

V+

C2

10uF

-20.00V

Q3 Q2N2222

14.13uA

2.409mA-2.423mA

0

20.00V

V+

R5

1k

2.898mA

V+V

0

C3

10uF

R2

10k

386.1uA

V+

R6

150k

104.6uA0

0V

5.598V

RL

20k

0A

4.310V

3.861V

R9

10k

2.423mA

Rs

500A 0V

V+

C6

10uF

C1

10uFR10

10k489.4uA

0

10.37V

V+

R4

100

2.898mA

0V

0

0

0

V11mVac0Vdc

0A

0

R11

30k 503.5uA

R12

4k

2.409mA

V-

20Vdc

2.423mA

V-

0V

0

V0V

R8

1k

3.636mA

20.00V

R7

50k

86.21uA

V-

0V2.898V

20.00V

Q2

Q2N222218.39uA

3.617mA

-3.636mA

V+

Multistage BJT amplifier II

Frequency

10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHzV(C6:1) V(V1:+)

0V

1.0V

2.0V

3.0V

4.0V

AC sweep from 10mHz to 10GHz

The amplifier is linear from about 288Hz to 1.602MHz. The voltage gain in the midband is about 3262. The gain is high so the bandwidth is reduced.

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Bipolar Junction Transistor AC/SMALL-SIGNAL ANALYSIS - MIDBAND Common emitter configuration

Q1

40239

Vin

-

0

C

+

0

B

E

Vcc

R3

icR2

+

R1

Rc

-

0

Vout

0

C

+

ic=gmVbe

0

Rc

E

R1

rpi

R2

BVout

r0

-

+

Vout

R3

Vin

-

rR 1 CRrR ||02 mm

e ggrR

13

CcoutCCcout RiVRrRriV 00 || BEin VV

CmBE

CBEm

BE

Cc

in

outV Rg

V

RVg

V

Ri

V

VA

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Bipolar Junction Transistor AC/SMALL-SIGNAL ANALYSIS - MIDBAND Common emitter configuration

0

Rs

Rc

Vcc

Vcc

0

RL

0

Vs

0

R1

R2

Vout

B

Vs

0

Rout

0

RL

Vout

Vpi

C

0

RB=R1||R2 rpi

ic=gmVpi

Rs

ro

Vin

0

E

0

Rin

-

00

Rc

+

rRR Bin || coout RrR ||

VVin Lcomout RRrVgV ||||

Lcom

Lcom

in

outv RRrg

V

RRrVg

V

VA ||||

||||

Properties: high voltage gain, high input resistance, reduced bandwidth (Miller effect)

Page 17: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

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Common emitter configuration with degeneration

Rc

Vcc

R2

0

Vs

RL

0

R1

Rs

0

REAC

0

Vout

Vcc

0

REDC

Rc

0

E

rpi

+

RoutRin

0

ro

Ve0

C

+

RL-

0

Vin

ic=Bib

Rs B

RB=R1||R2

-0

Vpi

REAC

Vout

Vs

eEACBEACBin rRRRrRR 1||1||

ccoout RRrR ||* EACmoo Rgrr 1*

EACbEACbbEACebEACcbbein RriRiriRiriRiiriVVV 11

eEACb rRi 1

Lcbout RRiV ||

eEAC

Lc

eEAC

Lc

eEACb

Lcb

in

outv rR

RR

rR

RR

rRi

RRi

V

VA

||

1

||

1

||

Properties: REAC increases the input resistance and lowers the voltage gain

Page 18: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

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Common collector/Emitter follower configuration

RL

Vcc

R2

0

00

Vout

R1

0

Vs

Rs

RE

Vcc

-

Vout

0

Rs

Vpi+

0

RB=R1||R2

Rout

0

ic=Bib

Vin E

RLVs

0

B rpi

C

0

Rin

0

ro RE

LEoeBLEoBin RRrrRRRrrRR ||||1||||||1||

1

||||||

SBEoout

RRrRrR

LEobLEobbin RRrriRRririV ||||1||||1

Loutbout RRiV ||1

LEoe

Lout

LEo

Lout

LEob

Loutb

in

outv RRrr

RR

RRrr

RR

RRrri

RRi

V

VA

||||

||

||||1

||1

||||1

||1

Properties: voltage gain close to 1, very high input resistance, very low output resistance

Page 19: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

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Common base configuration

Vcc

Vcc

0

R1

RE

0 Vs

Vout

0Rs

VEE

Rc

0

R2

RL

Rc

ic=aie

0 B

Vout

Vpi ie

-

Rs

0

Vs

Rin

RL

E

0

ro

re

Rout

0

Vin

+

C

0

RE

Actual circuit

Page 20: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

20 www.ice77.net

0

Rs

0

Rin

VinE

reVpi

RL

0

REVs

0

ic=aie

0

Rout

C

+

B

-

0

Vout

Rcie

Simplified circuit

eEin rRR || CCoout RRrR ||

eein riVV LCeout RRiV ||

LCm

e

LC

ee

LCe

in

outv RRg

r

RR

ri

RRi

V

VA ||

||||

Properties: very high voltage gain, very low input resistance, high bandwidth

Page 21: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

21 www.ice77.net

Bipolar Junction Transistor AC/SMALL-SIGNAL ANALYSIS - LOW FREQUENCY The bandwidth of the BJT is limited in the low frequency range by the external capacitances CB, CC and CE. These capacitances set the lower cutoff frequency fL. Common emitter configuration

0

Vcc

0

RL

Cc

Vcc

0

R2

CB

R1

Rs

Vout

Vs

Rc

0

RB=R1||R2

0 00

rpi

Rs C

Vs

E

ic=gmVpi

Vpi

0

Rc

B

RL

0

+

Cc

ro

0

CB

-

0

BBSB CrRR || CLCoC CRRr ||

n

nL

1

2

LLf

Page 22: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

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Common emitter configuration with degeneration

R2 REAC

RL

0

0

Cc

Vcc

0

R1

0

Rs

Vcc

Vs

Rc

CB

0 REDCCE

Vout

CE

rpi

- RL

Rs

0

E

ic=gmVpi

Rc

REAC

RB=R1||R2Vs

Vpi

0

+

0

ro

REDC

0

0

0

CB C CcB

BEACBSBLCoEACBSB CRrRRCRRrRrRR ||||||||

CCLCBS

EACoCLC CRRCRRr

RrRR

1

||||||

EBS

EACEDCELCoBS

EACEDCE CRRr

RRCRRrRRr

RR

1

||||||||

1

||||

n

nL

1

2

LLf

Page 23: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

23 www.ice77.net

Common collector configuration

Vs

0

CB

Vcc

Vcc

RL

0

0

R2

R1

CE

Rs

RE

0

Vout

0

Vs

rpiRs CE

RE

+

ic=gmVbe

Vbe

0

-

B

0

ro

0

RL

ECB

0

C

0

RB=R1||R2

BSBLEoB CRRrRRr ||||||

ELEoBSE CRRrrRR ||||||

n

nL

1

2

LLf

Page 24: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

24 www.ice77.net

Common base configuration

CB

Vout

CE

R2

0

0

0

Vs

Vcc

RE

RL

VEE

Rs

Vcc

0

R1

Rc

Cc

RL

ro

Vs

0

ECE

RE

0

+

-

Rs

Rc

CcC

0

re

0 B0

Vpi

ic=aie

Actual circuit

Page 25: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

25 www.ice77.net

0 B

RLre

CE

Rc

0

Vs-

0

Vpi

Rs

+

E

ic=aie

CcC

0 0

RE

Simplified circuit

EeESE CrRR ||

CLCC CRR

n

nL

1

2

LLf

Page 26: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

26 www.ice77.net

Bipolar Junction Transistor AC/SMALL-SIGNAL ANALYSIS - HIGH FREQUENCY The bandwidth of the BJT is limited in the high frequency range by the internal capacitances Cπ and Cμ. These capacitances set the higher cutoff frequency fH. Common emitter configuration

Vcc

00

R1VoutCc

Vcc

Rc

CBRs

0

R2Vs

0

RL

00

B

ro

0 0

+

0

RLRB=R1||R2 rpi

0 0

Rc

0

Cpi

E

CCmu

Vpi

ic=gmVpi

-

Vs

Rs

Actual circuit

Cpi CLCM

0

RB=R1||R2 ro

Rs

-

0

B

0

+

0 0 0

E

0

C

RcVs

Vpi rpi

ic=gm*Vpi

0 00

RL

Simplified circuit

MBSi CCrRR |||| )1( KCCM

LLCoo CRRr |||| CK

CCL

11

n

n

H

1

2

HHf

Page 27: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

27 www.ice77.net

Common emitter configuration with degeneration

0

R2

0

Rc

0

Rs

Vcc

RL

0

R1

REDC

REAC

0

CB

Vout

CE

Cc

Vs

Vcc

0

RL

0 0

Rs

REAC0 0

CpiRcRB=R1||R2

rpiVs

-

+

Vbe

Cmu CB

E

roic=gmVbe

Actual circuit

0

CLVs

0 00

Vbeic=gm*Vbe

E

Cpi*

0 0

B

CM

00

RB=R1||R2

0

RL

C

0

+

Rs

-

rpi* ro* Rc

Simplified circuit

EACm

mm Rg

gg

1*

Page 28: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

28 www.ice77.net

MBSi CCrRR **||||

EACm Rgrr 1*

EACm Rg

CC

1* )1( KCCM

LLCoo CRRr ||||*

EACmoo Rgrr 1* CK

CCL

11

n

n

H

1

2

HHf

Page 29: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

29 www.ice77.net

Common collector configuration

Vs

0

CB

Vcc

Vcc

RL

0

0

R2

R1

CE

Rs

RE

0

Vout

RLRE

0

Vbe

0

E

0000 0

+

B

ic=gmVbeCL

Cpi

Cmu

0

Vs

C

-

Rs rpi

RB=R1||R2 ro

Actual circuit

Rs

0 0 0

RLrpi**

0

ro

0

C

00

B

ic=gmVbe

0

REVs

rpi*

E

0

Cmu CLCM

0 0

RB=R1||R2

Simplified circuit

MBSi CCrRR *||||

K

rr

1* )1( KCCM

LLEoo CRRrr |||||| **

K

rr

11

**

CK

CCL

11

n

n

H

1

2

HHf

Page 30: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

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Common base configuration

CB

Vout

CE

R2

0

0

0

Vs

Vcc

RE

RL

VEE

Rs

Vcc

0

R1

Rc

Cc

+

Rs C

00

CmuRcVs

00

RL

ro

ic=aie

-

0

reVpi

0 B

RE Cpi

E

0 Actual circuit

Page 31: Bipolar Junction Transistors - ICE77 · Bipolar Junction Transistors The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals

31 www.ice77.net

+

0 0

Cpire

0

Rc

B

ic=aie

Vpi

-

RL

E

0 00

VsRE Cmu

C

0

Rs

Simplified circuit

CrRR eESi ||||

CRR LCo ||

n

n

H

1

2

HHf

Note: the common base configuration is not affected by Miller capacitance because the base of the amplifier is grounded.