# Common Emitter Amplifier Effects On A Circuit Technology Essay

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In this lab, we will be connected a common emitter amplifier circuit to observe the effects on the circuit and circuit gain with a bypass capacitor in the circuit and without. And will calculate the gain of the circuit both with and without a bypass capacitor to see the effect the component has on the circuit, as well as calculate or measure the cut off frequency of the circuit

Practical Measurement

2.1 Experimental Circuit

Figure 1: Schematic diagram reproduced using ISIS

## Experimental Equipment and Components

Regulated DC supply

Project Board

Coupling wires

Function generator

Oscilloscope

Two BC 337 NPN transistor

Resistors (56kâ„¦, 22kâ„¦, 180â„¦, 5.1kâ„¦, 3.3kâ„¦, 10kâ„¦ and 1kâ„¦)

Capacitors (330nF, 470pF(-2), 220µF and 10µF)

## Experimental Procedure

Build the circuit in figure1, which is only left hand side of the line AB without any capacitors.

Connect the power supply only after double-checking all connections, especially the transistor leads.

Measure the DC voltage at the emitter, the base and the collector.

Use a VOM to measure the dc voltage from collector to emitter (it should be about 5V), from base to emitter (0.6 - 0.7 V), and from collector and emitter to ground (7 V and 2 V, respectively).

Measure the DC voltage at the nodes.

Add the capacitors to the circuit and CL+RL load to the collector or Q1.

Apply a very low amplitude sine wave (20mV peak to peak) and find the gain at 5 KHz.

Measure the frequency response of the amplifier, varying the frequency from 50Hz to 1MHz and plot a graph.

Find the low and high cut off frequencies.

## Experimental Results

DC Characteristics at the emitter, the base and the collector

VBB1 = 4.0V

VBE1 = 587mV

VB1 = 4.01V

VE1 = 3.48V

VC1 = 9.23V

According to measured values,

Current in Emitter IE1 = VE1 / RE1

= 3.48V / 3.3 - 103 â„¦

= 1.054mA

So, IC1≈ IE1 = 1.054mA

Thus gM1 = 1.054mA / 26mV {gM1 = IC / VT, where VT = 26mV}

= 0.041S

So, rπ1 = 210 / 0.041 { rπ1 = β / gM , β = 210 }

= 5121.95â„¦ or 5.12Kâ„¦

Mid Band frequency

Vin(mV)

Vout(mV)

5Khz

20

800

Mid band gain = Vout / Vin

= 800 &divide; 20

= 40

Gain in dB = 20log10 (40)

= 32.04dB

Frequency Response of single Amplifier with Single Cc

Table of measured values of the frequency response, varying the frequency from 50Hz to 1MHz and the graph,

## Gain dB

50

20

0

0

0

100

20

500

25

27.95880017

200

20

700

35

30.88136089

400

20

750

37.5

31.48062535

500

20

760

38

31.59567193

600

20

800

40

32.04119983

800

20

800

40

32.04119983

1K

20

800

40

32.04119983

2K

20

800

40

32.04119983

4K

20

800

40

32.04119983

5K

20

800

40

32.04119983

6K

20

800

40

32.04119983

8K

20

800

40

32.04119983

10K

20

800

40

32.04119983

20K

20

750

37.5

31.48062535

40K

20

650

32.5

30.23766722

50K

20

550

27.5

28.78665388

60K

20

500

25

27.95880017

80K

20

400

20

26.02059991

100K

20

300

15

23.52182518

200K

20

180

9

19.08485019

400K

20

100

5

13.97940009

500K

20

80

4

12.04119983

600K

20

60

3

9.542425094

800K

20

40

2

6.020599913

1M

20

20

1

0

Figure 2: Frequency response graph of single capacitor

In single capacitor frequency response graph the cut off frequency occurs 3dB below the maximum gain. From the frequency response table in the lab sheet the maximum gain is 32.04 dB. So the cut-off frequency occurs at 29.04dB.

From the graph

Low Cut - Off frequency

100Hz

High Cut - Off frequency

49KHz

Bandwidth

49KHz - 100Hz = 48.9KHz

Frequency Response of single Amplifier with Double Cc

This experiment was not done in the lap due to limited time in the lap. So I use PSPICE to simulate the graph to find the cut off frequencies in result analysis.

## DC Conditions of single Amplifier

For circuit1 PSPICE simulation

Circuit for DC Characteristics

**** 03/15/111 14:25:27 ******** NT Evaluation PSpice (July 1997) ************

## *

**** CIRCUIT DESCRIPTION

R1 1 2 56k

R2 1 0 22k

Rb 1 4 0.18k

Rc 2 3 5.1k

Re 5 0 3.3k

VCC 2 0 15v

Q1 3 4 5 QBC337-25

.MODEL QBC337-25 NPN(

+ IS = 4.13E-14

+ NF = 0.9822

+ ISE = 3.534E-15

+ NE = 1.35

+ BF = 292.4

+ IKF = 0.9

+ VAF = 145.7

+ NR = 0.982

+ ISC = 1.957E-13

+ NC = 1.3

+ BR = 23.68

+ IKR = 0.1

+ VAR = 20

+ RB = 60

+ IRB = 0.0002

+ RBM = 8

+ RE = 0.1129

+ RC = 0.25

+ XTB = 0

+ EG = 1.11

+ XTI = 3

+ CJE = 3.799E-11

+ VJE = 0.6752

+ MJE = 0.3488

+ TF = 5.4E-10

+ XTF = 4

+ VTF = 4.448

+ ITF = 0.665

+ PTF = 90

+ CJC = 1.355E-11

+ VJC = 0.3523

+ MJC = 0.3831

+ XCJC = 0.455

+ TR = 3E-08

+ CJS = 0

+ VJS = 0.75

+ MJS = 0.333

+ FC = 0.643)

.op

**** 03/15/111 14:25:27 ******** NT Evaluation Pspice (July 1997) ************

## *

**** BJT MODEL PARAMETERS

QBC337-25

NPN

IS 41.300000E-15

BF 292.4

NF .9822

VAF 145.7

IKF .9

ISE 3.534000E-15

NE 1.35

BR 23.68

NR .982

VAR 20

IKR .1

ISC 195.700000E-15

NC 1.3

RB 60

RBM 8

IRB 200.000000E-06

RE .1129

RC .25

CJE 37.990000E-12

VJE .6752

MJE .3488

CJC 13.550000E-12

VJC .3523

MJC .3831

XCJC .455

MJS .333

FC .643

TF 540.000000E-12

XTF 4

VTF 4.448

ITF .665

PTF 90

TR 30.000000E-09

**** 03/15/111 14:25:27 ******** NT Evaluation Pspice (July 1997) ************

## *

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE

( 1) 4.1709 ( 2) 15.0000 ( 3) 9.5164 ( 4) 4.1702

( 5) 3.5607

VOLTAGE SOURCE CURRENTS

NAME CURRENT

VCC -1.269E-03

TOTAL POWER DISSIPATION 1.90E-02 WATTS

**** 03/15/111 14:25:27 ******** NT Evaluation Pspice (July 1997) ************

## *

**** OPERATING POINT INFORMATION TEMPERATURE = 27.000 DEG C

**** BIPOLAR JUNCTION TRANSISTORS

NAME Q1

MODEL QBC337-25

IB 3.79E-06

IC 1.08E-03

VBE 6.09E-01

VBC -5.35E+00

VCE 5.96E+00

GM 4.22E-02

RPI 6.76E+03

RX 5.79E+01

RO 1.36E+05

CBE 9.10E-11

CBC 2.12E-12

CJS 0.00E+00

BETAAC 2.86E+02

CBX 2.54E-12

FT 7.02E+07

JOB CONCLUDED

TOTAL JOB TIME .70

## Frequency Response of Single Amplifier with Single Cc

For circuit2 PSPICE simulation

Single Amp with single Capacitor

**** 03/15/111 14:30:42 ******** NT Evaluation PSpice (July 1997) ************

## *

**** CIRCUIT DESCRIPTION

## ******************************************************************************

R1 1 2 56k

R2 1 0 22k

Rb 1 4 0.18k

Rc 2 3 5.1k

Re 5 0 3.3k

RL 7 0 1k

VAC 6 0 ac 20MV

VCC 2 0 15v

Cin 6 1 330nF

Cc 4 3 470pF

CE 5 0 220uF

CL 3 7 10uF

Q1 3 4 5 QBC337-25

.MODEL QBC337-25 NPN(

+ IS = 4.13E-14

+ NF = 0.9822

+ ISE = 3.534E-15

+ NE = 1.35

+ BF = 292.4

+ IKF = 0.9

+ VAF = 145.7

+ NR = 0.982

+ ISC = 1.957E-13

+ NC = 1.3

+ BR = 23.68

+ IKR = 0.1

+ VAR = 20

+ RB = 60

+ IRB = 0.0002

+ RBM = 8

+ RE = 0.1129

+ RC = 0.25

+ XTB = 0

+ EG = 1.11

+ XTI = 3

+ CJE = 3.799E-11

+ VJE = 0.6752

+ MJE = 0.3488

+ TF = 5.4E-10

+ XTF = 4

+ VTF = 4.448

+ ITF = 0.665

+ PTF = 90

+ CJC = 1.355E-11

+ VJC = 0.3523

+ MJC = 0.3831

+ XCJC = 0.455

+ TR = 3E-08

+ CJS = 0

+ VJS = 0.75

+ MJS = 0.333

+ FC = 0.643)

.op

.ac DEC 100 1 100K

.PROBE

**** 03/15/111 14:30:42 ******** NT Evaluation PSpice (July 1997) ************

## *

**** BJT MODEL PARAMETERS

## ******************************************************************************

QBC337-25

NPN

IS 41.300000E-15

BF 292.4

NF .9822

VAF 145.7

IKF .9

ISE 3.534000E-15

NE 1.35

BR 23.68

NR .982

VAR 20

IKR .1

ISC 195.700000E-15

NC 1.3

RB 60

RBM 8

IRB 200.000000E-06

RE .1129

RC .25

CJE 37.990000E-12

VJE .6752

MJE .3488

CJC 13.550000E-12

VJC .3523

MJC .3831

XCJC .455

MJS .333

FC .643

TF 540.000000E-12

XTF 4

VTF 4.448

ITF .665

PTF 90

TR 30.000000E-09

**** 03/15/111 14:30:42 ******** NT Evaluation PSpice (July 1997) ************

## *

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE

( 1) 4.1709 ( 2) 15.0000 ( 3) 9.5164 ( 4) 4.1702

( 5) 3.5607 ( 6) 0.0000 ( 7) 0.0000

VOLTAGE SOURCE CURRENTS

NAME CURRENT

VAC 0.000E+00

VCC -1.269E-03

TOTAL POWER DISSIPATION 1.90E-02 WATTS

**** 03/15/111 14:30:42 ******** NT Evaluation PSpice (July 1997) ************

## *

**** OPERATING POINT INFORMATION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

**** BIPOLAR JUNCTION TRANSISTORS

NAME Q1

MODEL QBC337-25

IB 3.79E-06

IC 1.08E-03

VBE 6.09E-01

VBC -5.35E+00

VCE 5.96E+00

GM 4.22E-02

RPI 6.76E+03

RX 5.79E+01

RO 1.36E+05

CBE 9.10E-11

CBC 2.12E-12

CJS 0.00E+00

BETAAC 2.86E+02

CBX 2.54E-12

FT 7.02E+07

JOB CONCLUDED

TOTAL JOB TIME 4.95

## Frequency Response of Single Amplifier with Double Cc

For circuit2 with double capacitor PSPICE simulation

Single Amp with Double Capacitor

**** 03/15/111 14:39:57 ******** NT Evaluation PSpice (July 1997) ************

## *

**** CIRCUIT DESCRIPTION

## ******************************************************************************

R1 1 2 56k

R2 1 0 22k

Rb 1 4 0.18k

Rc 2 3 5.1k

Re 5 0 3.3k

RL 7 0 1k

VAC 6 0 ac 20MV

VCC 2 0 15v

Cin 6 1 330nF

Cc 4 3 470pF

Cc2 4 3 470pF

CE 5 0 220uF

CL 3 7 10uF

Q1 3 4 5 QBC337-25

.MODEL QBC337-25 NPN(

+ IS = 4.13E-14

+ NF = 0.9822

+ ISE = 3.534E-15

+ NE = 1.35

+ BF = 292.4

+ IKF = 0.9

+ VAF = 145.7

+ NR = 0.982

+ ISC = 1.957E-13

+ NC = 1.3

+ BR = 23.68

+ IKR = 0.1

+ VAR = 20

+ RB = 60

+ IRB = 0.0002

+ RBM = 8

+ RE = 0.1129

+ RC = 0.25

+ XTB = 0

+ EG = 1.11

+ XTI = 3

+ CJE = 3.799E-11

+ VJE = 0.6752

+ MJE = 0.3488

+ TF = 5.4E-10

+ XTF = 4

+ VTF = 4.448

+ ITF = 0.665

+ PTF = 90

+ CJC = 1.355E-11

+ VJC = 0.3523

+ MJC = 0.3831

+ XCJC = 0.455

+ TR = 3E-08

+ CJS = 0

+ VJS = 0.75

+ MJS = 0.333

+ FC = 0.643)

.op

.ac DEC 100 1 100K

.PROBE

**** 03/15/111 14:39:57 ******** NT Evaluation PSpice (July 1997) ************

## *

**** BJT MODEL PARAMETERS

## ******************************************************************************

QBC337-25

NPN

IS 41.300000E-15

BF 292.4

NF .9822

VAF 145.7

IKF .9

ISE 3.534000E-15

NE 1.35

BR 23.68

NR .982

VAR 20

IKR .1

ISC 195.700000E-15

NC 1.3

RB 60

RBM 8

IRB 200.000000E-06

RE .1129

RC .25

CJE 37.990000E-12

VJE .6752

MJE .3488

CJC 13.550000E-12

VJC .3523

MJC .3831

XCJC .455

MJS .333

FC .643

TF 540.000000E-12

XTF 4

VTF 4.448

ITF .665

PTF 90

TR 30.000000E-09

**** 03/15/111 14:39:57 ******** NT Evaluation PSpice (July 1997) ************

## *

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE

( 1) 4.1709 ( 2) 15.0000 ( 3) 9.5164 ( 4) 4.1702

( 5) 3.5607 ( 6) 0.0000 ( 7) 0.0000

VOLTAGE SOURCE CURRENTS

NAME CURRENT

VAC 0.000E+00

VCC -1.269E-03

TOTAL POWER DISSIPATION 1.90E-02 WATTS

**** 03/15/111 14:39:57 ******** NT Evaluation PSpice (July 1997) ************

## *

**** OPERATING POINT INFORMATION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

**** BIPOLAR JUNCTION TRANSISTORS

NAME Q1

MODEL QBC337-25

IB 3.79E-06

IC 1.08E-03

VBE 6.09E-01

VBC -5.35E+00

VCE 5.96E+00

GM 4.22E-02

RPI 6.76E+03

RX 5.79E+01

RO 1.36E+05

CBE 9.10E-11

CBC 2.12E-12

CJS 0.00E+00

BETAAC 2.86E+02

CBX 2.54E-12

FT 7.02E+07

JOB CONCLUDED

TOTAL JOB TIME 5.24

## DC conditions of Cascaded Amplifier

For circuit3 DC Characteristics PSPICE simulation

Circuit for DC Characteristics

**** 03/15/111 14:54:02 ******** NT Evaluation PSpice (July 1997) ************

## *

**** CIRCUIT DESCRIPTION

## ******************************************************************************

R1 1 2 56k

R2 1 0 22k

Rb 1 4 0.18k

Rc 2 3 5.1k

Re 5 0 3.3k

Re2 6 0 10k

VCC 2 0 15v

Q1 3 4 5 QBC337-25

Q2 2 3 6 QBC337-25

.MODEL QBC337-25 NPN(

+ IS = 4.13E-14

+ NF = 0.9822

+ ISE = 3.534E-15

+ NE = 1.35

+ BF = 292.4

+ IKF = 0.9

+ VAF = 145.7

+ NR = 0.982

+ ISC = 1.957E-13

+ NC = 1.3

+ BR = 23.68

+ IKR = 0.1

+ VAR = 20

+ RB = 60

+ IRB = 0.0002

+ RBM = 8

+ RE = 0.1129

+ RC = 0.25

+ XTB = 0

+ EG = 1.11

+ XTI = 3

+ CJE = 3.799E-11

+ VJE = 0.6752

+ MJE = 0.3488

+ TF = 5.4E-10

+ XTF = 4

+ VTF = 4.448

+ ITF = 0.665

+ PTF = 90

+ CJC = 1.355E-11

+ VJC = 0.3523

+ MJC = 0.3831

+ XCJC = 0.455

+ TR = 3E-08

+ CJS = 0

+ VJS = 0.75

+ MJS = 0.333

+ FC = 0.643)

.op

**** 03/15/111 14:54:02 ******** NT Evaluation PSpice (July 1997) ************

## *

**** BJT MODEL PARAMETERS

## ******************************************************************************

QBC337-25

NPN

IS 41.300000E-15

BF 292.4

NF .9822

VAF 145.7

IKF .9

ISE 3.534000E-15

NE 1.35

BR 23.68

NR .982

VAR 20

IKR .1

ISC 195.700000E-15

NC 1.3

RB 60

RBM 8

IRB 200.000000E-06

RE .1129

RC .25

CJE 37.990000E-12

VJE .6752

MJE .3488

CJC 13.550000E-12

VJC .3523

MJC .3831

XCJC .455

MJS .333

FC .643

TF 540.000000E-12

XTF 4

VTF 4.448

ITF .665

PTF 90

TR 30.000000E-09

**** 03/15/111 14:54:02 ******** NT Evaluation PSpice (July 1997) ************

## *

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE

( 1) 4.1709 ( 2) 15.0000 ( 3) 9.5005 ( 4) 4.1702

( 5) 3.5607 ( 6) 8.8960

VOLTAGE SOURCE CURRENTS

NAME CURRENT

VCC -2.158E-03

TOTAL POWER DISSIPATION 3.24E-02 WATTS

**** 03/15/111 14:54:02 ******** NT Evaluation PSpice (July 1997) ************

## *

**** OPERATING POINT INFORMATION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

**** BIPOLAR JUNCTION TRANSISTORS

NAME Q1 Q2

MODEL QBC337-25 QBC337-25

IB 3.79E-06 3.13E-06

IC 1.08E-03 8.86E-04

VBE 6.09E-01 6.04E-01

VBC -5.33E+00 -5.50E+00

VCE 5.94E+00 6.10E+00

GM 4.22E-02 3.48E-02

RPI 6.76E+03 8.21E+03

RX 5.79E+01 5.82E+01

RO 1.36E+05 1.66E+05

CBE 9.10E-11 8.66E-11

CBC 2.12E-12 2.10E-12

CJS 0.00E+00 0.00E+00

BETAAC 2.86E+02 2.86E+02

CBX 2.55E-12 2.52E-12

FT 7.02E+07 6.07E+07

JOB CONCLUDED

TOTAL JOB TIME .69

## Frequency Response of Cascaded Amplifier with single Cc

For circuit4 PSPICE simulation

**** 03/15/111 15:19:46 ******** NT Evaluation PSpice (July 1997) ************

## *

**** CIRCUIT DESCRIPTION

## ******************************************************************************

R1 1 2 56k

R2 1 0 22k

Rb 1 4 0.18k

Rc 2 3 5.1k

Re 5 0 3.3k

Re2 6 0 10k

RL 8 0 1K

Cin 7 1 330nF

Cc 4 3 470pF

Ce 5 0 220uF

CL 6 8 10uF

VCC 2 0 15v

VAC 7 0 ac 20MV

Q1 3 4 5 QBC337-25

Q2 2 3 6 QBC337-25

.MODEL QBC337-25 NPN(

+ IS = 4.13E-14

+ NF = 0.9822

+ ISE = 3.534E-15

+ NE = 1.35

+ BF = 292.4

+ IKF = 0.9

+ VAF = 145.7

+ NR = 0.982

+ ISC = 1.957E-13

+ NC = 1.3

+ BR = 23.68

+ IKR = 0.1

+ VAR = 20

+ RB = 60

+ IRB = 0.0002

+ RBM = 8

+ RE = 0.1129

+ RC = 0.25

+ XTB = 0

+ EG = 1.11

+ XTI = 3

+ CJE = 3.799E-11

+ VJE = 0.6752

+ MJE = 0.3488

+ TF = 5.4E-10

+ XTF = 4

+ VTF = 4.448

+ ITF = 0.665

+ PTF = 90

+ CJC = 1.355E-11

+ VJC = 0.3523

+ MJC = 0.3831

+ XCJC = 0.455

+ TR = 3E-08

+ CJS = 0

+ VJS = 0.75

+ MJS = 0.333

+ FC = 0.643)

.op

.ac DEC 100 1 100K

.PROBE

**** 03/15/111 15:19:46 ******** NT Evaluation PSpice (July 1997) ************

## *

**** BJT MODEL PARAMETERS

## ******************************************************************************

QBC337-25

NPN

IS 41.300000E-15

BF 292.4

NF .9822

VAF 145.7

IKF .9

ISE 3.534000E-15

NE 1.35

BR 23.68

NR .982

VAR 20

IKR .1

ISC 195.700000E-15

NC 1.3

RB 60

RBM 8

IRB 200.000000E-06

RE .1129

RC .25

CJE 37.990000E-12

VJE .6752

MJE .3488

CJC 13.550000E-12

VJC .3523

MJC .3831

XCJC .455

MJS .333

FC .643

TF 540.000000E-12

XTF 4

VTF 4.448

ITF .665

PTF 90

TR 30.000000E-09

**** 03/15/111 15:19:46 ******** NT Evaluation PSpice (July 1997) ************

## *

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE

( 1) 4.1709 ( 2) 15.0000 ( 3) 9.5005 ( 4) 4.1702

( 5) 3.5607 ( 6) 8.8960 ( 7) 0.0000 ( 8) 0.0000

VOLTAGE SOURCE CURRENTS

NAME CURRENT

VCC -2.158E-03

VAC 0.000E+00

TOTAL POWER DISSIPATION 3.24E-02 WATTS

**** 03/15/111 15:19:46 ******** NT Evaluation PSpice (July 1997) ************

## *

**** OPERATING POINT INFORMATION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

**** BIPOLAR JUNCTION TRANSISTORS

NAME Q1 Q2

MODEL QBC337-25 QBC337-25

IB 3.79E-06 3.13E-06

IC 1.08E-03 8.86E-04

VBE 6.09E-01 6.04E-01

VBC -5.33E+00 -5.50E+00

VCE 5.94E+00 6.10E+00

GM 4.22E-02 3.48E-02

RPI 6.76E+03 8.21E+03

RX 5.79E+01 5.82E+01

RO 1.36E+05 1.66E+05

CBE 9.10E-11 8.66E-11

CBC 2.12E-12 2.10E-12

CJS 0.00E+00 0.00E+00

BETAAC 2.86E+02 2.86E+02

CBX 2.55E-12 2.52E-12

FT 7.02E+07 6.07E+07

JOB CONCLUDED

TOTAL JOB TIME 5.59

## . Frequency Response of Cascaded Amplifier with double Cc

For circuit 4 PSPICE simulations

**** 03/15/111 15:31:32 ******** NT Evaluation PSpice (July 1997) ************

## *

**** CIRCUIT DESCRIPTION

## ******************************************************************************

R1 1 2 56k

R2 1 0 22k

Rb 1 4 0.18k

Rc 2 3 5.1k

Re 5 0 3.3k

Re2 6 0 10k

RL 8 0 1K

Cin 7 1 330nF

Cc 4 3 470pF

Cc2 4 3 470pF

Ce 5 0 220uF

CL 6 8 10uF

VCC 2 0 15v

VAC 7 0 ac 20MV

Q1 3 4 5 QBC337-25

Q2 2 3 6 QBC337-25

.MODEL QBC337-25 NPN(

+ IS = 4.13E-14

+ NF = 0.9822

+ ISE = 3.534E-15

+ NE = 1.35

+ BF = 292.4

+ IKF = 0.9

+ VAF = 145.7

+ NR = 0.982

+ ISC = 1.957E-13

+ NC = 1.3

+ BR = 23.68

+ IKR = 0.1

+ VAR = 20

+ RB = 60

+ IRB = 0.0002

+ RBM = 8

+ RE = 0.1129

+ RC = 0.25

+ XTB = 0

+ EG = 1.11

+ XTI = 3

+ CJE = 3.799E-11

+ VJE = 0.6752

+ MJE = 0.3488

+ TF = 5.4E-10

+ XTF = 4

+ VTF = 4.448

+ ITF = 0.665

+ PTF = 90

+ CJC = 1.355E-11

+ VJC = 0.3523

+ MJC = 0.3831

+ XCJC = 0.455

+ TR = 3E-08

+ CJS = 0

+ VJS = 0.75

+ MJS = 0.333

+ FC = 0.643)

.op

.ac DEC 100 1 100K

.PROBE

**** 03/15/111 15:31:32 ******** NT Evaluation PSpice (July 1997) ************

## *

**** BJT MODEL PARAMETERS

## ******************************************************************************

QBC337-25

NPN

IS 41.300000E-15

BF 292.4

NF .9822

VAF 145.7

IKF .9

ISE 3.534000E-15

NE 1.35

BR 23.68

NR .982

VAR 20

IKR .1

ISC 195.700000E-15

NC 1.3

RB 60

RBM 8

IRB 200.000000E-06

RE .1129

RC .25

CJE 37.990000E-12

VJE .6752

MJE .3488

CJC 13.550000E-12

VJC .3523

MJC .3831

XCJC .455

MJS .333

FC .643

TF 540.000000E-12

XTF 4

VTF 4.448

ITF .665

PTF 90

TR 30.000000E-09

**** 03/15/111 15:31:32 ******** NT Evaluation PSpice (July 1997) ************

## *

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE

( 1) 4.1709 ( 2) 15.0000 ( 3) 9.5005 ( 4) 4.1702

( 5) 3.5607 ( 6) 8.8960 ( 7) 0.0000 ( 8) 0.0000

VOLTAGE SOURCE CURRENTS

NAME CURRENT

VCC -2.158E-03

VAC 0.000E+00

TOTAL POWER DISSIPATION 3.24E-02 WATTS

**** 03/15/111 15:31:32 ******** NT Evaluation PSpice (July 1997) ************

## *

**** OPERATING POINT INFORMATION TEMPERATURE = 27.000 DEG C

## ******************************************************************************

**** BIPOLAR JUNCTION TRANSISTORS

NAME Q1 Q2

MODEL QBC337-25 QBC337-25

IB 3.79E-06 3.13E-06

IC 1.08E-03 8.86E-04

VBE 6.09E-01 6.04E-01

VBC -5.33E+00 -5.50E+00

VCE 5.94E+00 6.10E+00

GM 4.22E-02 3.48E-02

RPI 6.76E+03 8.21E+03

RX 5.79E+01 5.82E+01

RO 1.36E+05 1.66E+05

CBE 9.10E-11 8.66E-11

CBC 2.12E-12 2.10E-12

CJS 0.00E+00 0.00E+00

BETAAC 2.86E+02 2.86E+02

CBX 2.55E-12 2.52E-12

FT 7.02E+07 6.07E+07

JOB CONCLUDED

TOTAL JOB TIME 5.61

## 4.1 DC Conditions of Single Amplifier

Theoretical values for DC Characteristics, which from PSPICE simulation voltage value,

VBB1 = 4.1709V

VBE1 = 0.609V

VB1 = 4.1702V

VE1 = 3.5607V

VC1 = 9.5164V

According to measured values,

Current in Emitter IE1 = VE1 / RE1

= 3.5607V / 3.3 - 103 â„¦

= 1.079mA

So, IC1≈ IE1 = 1.079mA

Thus gM1 = 1.079mA / 26mV {gM1 = IC / VT, where VT = 26mV}

= 0.0415S

So, rπ1 = 210 / 0.0415 { rπ1 = β / gM , β = 210 }

= 5060.24â„¦ or 5.06Kâ„¦

## 4.2 Frequency Response of single Amplifier with single Cc

In single capacitor frequency response graph from PSPICE [figure 4.2] the cut off frequency occurs 3dB below the maximum gain.

The maximum gain is 20log10 (641.784/20) = 30.12dB, so the cut-off frequency occurs at 27.12dB. Where the output voltage is 453.96mV

From the graph

Low Cut - Off frequency

113.922Hz

High Cut - Off frequency

49.436KHz

Bandwidth

49.322KHz

Figure 4.2

## 4.3. Frequency Response of single Amplifier with double Cc

In double capacitor frequency response graph from PSPICE [figure 4.3] the maximum gain is 20log10 (612.405/20) = 29.72dB, so the cut-off frequency occurs at 26.72dB. Where the output voltage is 433.54mV

From the graph

Low Cut - Off frequency

108.667Hz

High Cut - Off frequency

26.172KHz

Bandwidth

26.063KHz

Figure 4.3

## 4.4. DC Conditions of Cascaded Amplifier

Theoretical values for DC Characteristics, which from PSPICE simulation voltage value,

VBB2 = 4.1709V

VBE2 = 0.609V

VB2 = 9.5005V

VE2 = 8.896V

VC2 = 15V

According to measured values,

Current in Emitter IE2 = VE2 / RE2

= 8.896V / 3.3 - 103 â„¦

= 2.69mA

So, IC2≈ IE2 = 2.69mA

Thus gM2 = 2.69mA / 26mV {gM1 = IC / VT, where VT = 26mV}

= 0.103S

So, rπ2 = 210 / 0.103 { rπ1 = β / gM , β = 210 }

= 2038.83â„¦ or 2.04Kâ„¦

## 4.5. Frequency Response of Cascaded Amplifier with single Cc

In single capacitor frequency response of cascaded amplifier graph from PSPICE [figure4.5] the maximum gain is 20log10 (147.45/20) = 43.37dB, so the cut-off frequency occurs at 40.37dB. Where the output voltage is 2.046V

From the graph

Low Cut - Off frequency

88.135Hz

High Cut - Off frequency

11.174KHz

Bandwidth

11.085KHz

Figure 4.5

## 4.6. Frequency Response of Cascaded Amplifier with double Cc

In single capacitor frequency response of cascaded amplifier graph from PSPICE [figure 4.6] the maximum gain is 20log10 (2415/20) = 41.63dB, so the cut-off frequency occurs at 38.63dB. Where the output voltage is 1.708V

From the graph

Low Cut - Off frequency

73.506Hz

High Cut - Off frequency

6.638KHz

Bandwidth

6.564KHz

Figure 4.6

There can be some errors which affect on the readings in this experiment. These errors related To:

1.Thermal effect on the transistors and the resistors.

2. Personal errors.

3. The internal capacitance in the transistors.

4. Errors in the used devices.

5. The resolution in the measurement devices.

## Discussion

We noticed that the highest gain came from the circuit with the bypass capacitor in, and the lowest gain came from the circuit without the bypass capacitor. The circuit with the short across RE had a slightly higher gain than the one without the bypass capacitor, but it was still far less than the circuit using the bypass capacitor, which was about 50 times greater.

Shorting RE in the circuit causes an overall decrease in gain from when there was a bypass capacitor in the circuit. It is, however, an improvement from just having RE on the emitter lead. The gain increased by about 1 from the previous 1.38 gain value when the capacitor was taking out, but it far from as effective as when the bypass capacitor was in the circuit, which had a gain of 111.76. The current through IC also increased when RE was shorted

## Conclusion

In this lab, I have learned about common emitter amplifiers, and how the bypass capacitor works in the circuit, and what it does for the gain. I now know that the bypass capacitor improves the gain by almost 100 times that of the amplifier circuit without the capacitor. This allows someone to put the least amount of voltage into the circuit and get the most out. I have also learned the effects of taking the capacitor out of the circuit. The voltage gain decreased dramatically, as we saw from calculating the gains. The capacitor has the effect of needing more input voltage while getting less output voltage. This makes the circuit much less effective than if we had left the capacitor in. We also noticed the effects of replacing RE with a short from the emitter to ground. The gain is still extremely low, but not so much as the previous circuit. Shorting RE will give a slightly larger gain in the circuit without a capacitor. I've also learned how to calculate the gain of a circuit using the formula of Gain = Output / Input. This works for power gain, voltage gain, and current gain. So long as I have both the input and outputs of each, I can calculate each in turn using this formula.