DEPT OF ELECTRONIC, TELECOMMUNICATION & BIOMEDICAL ENGINEERING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO Electronics Lab#3 (1st Term, 2nd Year) 04 BM Lab Experiment# 2

Name: ________________________________________ Roll No: _________________ Score: _________ Signature of the Lab Tutor: ______________ Date: ______________

Amplifier Configurations Object: - To observe the working of bipolar junction transistor amplifier in following three configurations: 1. Common-emitter configuration 2. Common-collector configuration 3. Common-base configuration Equipment required: - F.B Trainer kit and power supply. Instruments required: - Function generator, Oscilloscope and a mili-ammeter. Introduction: - The circuit configuration specifies which terminals in the amplifier are used as input and output. Since NPN transistor is a three terminal device, therefore there are three possible configurations: the common base, common emitter and the common collector. The common terminal is usually is the one that does not have any signal. Common base amplifier: - In this type of configuration input signal is applied at the emitter with respect to grounded base. The amplified output is taken from the collector. This type of configuration has low input resistance and high output resistance. CB circuit is seldom used. It has no current gain from input to output. The voltage gain can be high. The only advantage of the CB circuit is that it has the best stability with an increase in temperature. O/P

I/P

Fig-1 Common-Base Amplifier Common Emitter Amplifier: - In Common emitter amplifier configuration input is applied to the base through a coupling capacitor with respect to the grounded emitter. The output voltage is still taken from the collector. This type of configuration has moderate input and output resistance ratio. The CE circuit has high current gain and the voltage

DEPT OF ELECTRONIC, TELECOMMUNICATION & BIOMEDICAL ENGINEERING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO Electronics Lab#3 (1st Term, 2nd Year) 04 BM Lab Experiment# 2

gain is same as the CB circuit. The CE amplifier is generally used for amplification because it has the combination of voltage gain and the current gain. CE amplifier inverts the signal voltage. This phase inversion of 180º is neither good nor bad but just the result of the circuit connection.

Fig-2 Common-Emitter Amplifier Common-Collector Amplifier: - In this amplifier input is applied at the base terminal and output is taken from emitter terminal and collector is made common to both input and output. In CC circuit input circuit has high resistance and out circuit has low resistance. There is no voltage gain in the CC circuit however this configuration has appreciable current gain. The name emitter follower is generally used for this circuit because the output signal at the emitter follows the polarity of the input signal at the base. The emitter follower is often used for the impedance matching from a high impedance source to low impedance load. This circuit also provides isolation between a load in the emitter circuit and the source in the base circuit.

Fig-3 Common-Collector Amplifier

DEPT OF ELECTRONIC, TELECOMMUNICATION & BIOMEDICAL ENGINEERING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO Electronics Lab#3 (1st Term, 2nd Year) 04 BM Lab Experiment# 2

Following table summarizes different characteristics of each type of configuration. Common Base Common Emitter Common Collector S.No Characteristic (CB) (CE) (CC) 1 Input terminal Emitter Base Base 2 Output terminal Collector Collector Emitter 3 Advantage Stability High gain High input resistance 4 Phase inversion No Yes No 5 Input resistance 20Ω 1000Ω 150KΩ 6 Output resistance 1MΩ 50KΩ 80Ω 7 Current gain Low High High 8 Voltage gain High High Low Note: Typical values are chosen with IE=1.5mA. Your observed values may differ slightly depending on the biasing conditions and load.

Observations: ¾ At which terminal you have applied the input signal to common base amplifier and from where you have taken the output?

¾ Have you observed any phase inversion

¾ Calculate the input and output resistance of the common base amplifier.

¾ How much voltage gain you have measured in this type of configuration?

¾ Calculate the current gain of common base amplifier.

¾ What are the input and output resistance values for common emitter amplifier?

¾ Calculate the Current and voltage gain of the Common emitter amplifier.

DEPT OF ELECTRONIC, TELECOMMUNICATION & BIOMEDICAL ENGINEERING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO Electronics Lab#3 (1st Term, 2nd Year) 04 BM Lab Experiment# 2

¾ Measure the values of Input and output resistance of CC Amplifier.

¾ Also measure the current and the voltage gain of CC amplifier.

¾ Have you compared all the readings with the given table?

¾ Which amplifier you will chose to get high power gain?

¾ Calculate the power gain of each amplifier.

Conclusion: -

DEPT OF ELECTRONIC, TELECOMMUNICATION & BIOMEDICAL ENGINEERING MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO Electronics Lab#3 (1st Term, 2nd Year) 04 BM Lab Experiment# 2

Review Questions ¾

What is impedance matching?

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What is the reason that input impedance of the CC amplifier is very high?

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Which type of configuration is widely used for amplification and why?

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What is the effect of phase inversion on CE amplifier?

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Define the following terms

Current Gain: -

Voltage Gain: -

Power Gain: -