Bjt Common Emitter Amplifier

Topics: Common emitter, Electronic amplifier, Gain Pages: 5 (718 words) Published: March 19, 2011
Electronic Analog 1 (EMT 112) Semester II 2009/2010

Exp . 1

UNIVERSITI MALAYSIA PERLIS

ANALOG ELECTRONICS 1 EMT 112/4

EXPERIMENT # 1 BJT COMMON EMITTER AMPLIFIER ‘Q’ POINT DC CURRENTS & VOLTAGES LOAD LINES VOLTAGE GAIN

MARKS
Pre Lab

DC I&V 5

βDC 1

5

re 1

Av 3

D 4

C 3

Total 25

NAME

PROGRAMME

MATRIK #

DATE

1

Electronic Analog 1 (EMT 112) Semester II 2009/2010

Exp . 1

EXPERIMENT 1 BJT Common Emitter Amplifier 1. OBJECTIVE:
1.1 DC OPERATIONAL EFFECTS The experimental objectives are to: i) Compare the amplifier theoretical and practical DC operational values, and in particular the ‘quiescent’ operating point (‘Q’ point). ii) Determine the effect of coupling capacitors and bypass capacitors on the ‘Q’ point. iii) Determine the effect of the load on the ‘Q’ point. iv) Determine the transistor operational βDC and compare with the 2N3904 data sheet. v) Draw the DC load line. 1.2 AC OPERATION The experimental objectives are to: i) Compare the theoretical and practical amplifier voltage gain. ii) Determine the effect of the load on the amplifier voltage gain. . iii) Observe the effect of unbypassed emitter resistors.

2.

INTRODUCTION:

In this lab, the common-emitter configuration will be investigated. This common-emitter amplifier typically uses a self biasing scheme and has a relatively linear output. The common-emitter amplifier is characterized by high voltage (Av) and current gain (Ai).The amplifier typically has a relatively high input resistance (1 to 10k ohms) and is generally used to drive medium to high resistance loads. The circuit for the common-emitter can be seen in Figure 1. It is used in applications where a small voltage signal needs to be amplified to a large voltage signal. Since the amplifier cannot drive low resistance loads, it is usually cascaded with a buffer that can acts as a driver.

FIGURE 1: Common Emitter Amplifier.

3.

EQUIPMENT:
2.1 2.2 2.3 2.4 Dual-trace oscilloscope Function Generator Voltmeter Breadboard

2

Electronic Analog 1 (EMT 112) Semester II 2009/2010

Exp . 1

4.

PROCEDURE: BJT COMMON EMITTER AMPLIFIER:

10.6V
20uAmp

20UAMP

FIGURE 2

PART A: DC OPERATION i) From FIGURE 2 amplifier circuit, do a pre lab calculation for DC operational conditions: (Assume βDC=100 VBE(ON)=0.7V) a) b) c) d) e) f) g) h) i) j) IC VE VCC VCE VB R1 re Zin Zout Gain Av (with C2 and without C2)

(5 M)

ii) Construct the amplifier circuit as shown in FIGURE 2.

3

Electronic Analog 1 (EMT 112) Semester II 2009/2010

Exp . 1

iii) Using a multimeter, measure DC currents and DC voltages with C2 and without C2 in the circuit. Record all the values. a. DC currents: IB, IC, IE. b. DC voltages: VCC, VB, VBE, VC, VCE, VE, Vload.

(5 M) (1 M) (3 M)

iv) Using IB and IC measurement values, calculate βDC. v) From the result, clearly indicate the major points and sketch a DC load line.

PART B: AC OPERATION

10.6V

20UAMP

FIGURE 3 i) ii) iii) iv) v) vi) Set both oscilloscope channels to ac coupled. Set gnd positions both channels. Set the signal generator input (VIN) as shown in FIGURE 3 to 0.1V peak-peak at 1 kHz. Reduce the input voltage if the output voltage waveform, CH2, is clipped By using IE measurement, calculate re .

(1 M) (3 M)

Find Voltage Gain Av (measurement) for amplifier circuit with C2 and without C2.

4

Electronic Analog 1 (EMT 112) Semester II 2009/2010

Exp . 1

5.

DISCUSSION:
i) In the DC equivalent circuit of an amplifier, how are the capacitors treated? (0.5 M) ii) When the emitter resistor is bypassed with a capacitor, how is the gain of the amplifier affected? (0.5 M) iii) What is the purpose of putting emitter resistor in the circuit? (1 M) iv) What is the phase relationship of the input and output voltage of common emitter amplifier? (0.5 M) v) State the function of input and output coupling capacitor, CC1 & CC2. (0.5 M) vi) Why do...