CE Amplifier PDF

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Electronic Devices CE Amplifier Write up...

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Ex.No: 2 Date: 10 September,2020 Characteristics of CE Amplifier Aim: To examine the Common Emitter (CE) Amplifier characteristic of a transistor. Components Required: S.No 1. 2. 3. 4. 5. 6. 7. 8. 9.

Component BJT – 2N2222 1 kΩ Resistor 6 kΩ Resistor 70 kΩ Resistor 12 kΩ Resistor Cathode-Ray Oscilloscope Connecting Wires Regulated Power Supply Breadboard

Quantity 1 1 1 1 1 1 1 1 1

Theory: Amplifiers are classified as small signal amplifiers and large signal amplifiers depending on the shift in operating point, from the quiescent condition caused by the input signal. If the shift is small, amplifiers are referred to as small signal amplifiers and if the shift is large, they are known as large signal amplifiers. In small signal amplifiers, voltage swing and current swing are small. Large signal amplifiers have large voltage swing and current swing and the signal power handled by such amplifiers remain large. Voltage amplifiers come under small signal amplifiers. Figure shows the circuit diagram of a common emitter amplifier. The gain of an ideal amplifier should remain the same for any frequency of the input signal. Therefore, the frequency response curve (gain in db plotted against frequency) becomes a straight line parallel to the frequency axis. In actual practice, the coupling capacitors and the emitter bypass capacitor reduce the gain at lower frequencies. The capacitance internal to the transistor and stray capacitance due to the wiring reduce the gain at higher frequencies.

Circuit Design: 𝑉𝐶𝐶 = 12𝑉, 𝑅𝐶 = 6𝑘Ω , 𝑅𝐸 = 1𝑘Ω , β = 100 Ic = 1mA , VCE = 5V. For DC bias-stable condition Rth = 0.1 β𝑅𝐸 = 0.1(100)(1) = 10 𝑘Ω Assuming IE ≈ IC , we get Vth = 1.7V. Using the relations , 𝑅1 =

𝑅𝑡ℎ 𝑉𝐶𝐶 𝑉𝑡ℎ

𝑎𝑛𝑑 𝑅2 =

𝑅1 𝑉𝑡ℎ 𝑉𝐶𝐶 −𝑉𝑡ℎ

we get 𝑅1 = 70.58 𝑘Ω and 𝑅2 = 11.64 𝑘Ω

Circuit Schematic:

Observation: Vin=100mV = 0.1V

Frequency(Hz) Amplitude(V) 10 14 20 30 40 60 180 280 1000 5000 9000 18000 20000 34000 50000 70000 80000 98000 140000 180000 230000 320000 360000 670000 700000 1000000

0.47 0.57 0.59 0.63 0.64 0.66 0.67 0.67 0.67 0.67 0.67 0.67 0.66 0.66 0.66 0.64 0.64 0.63 0.59 0.55 0.51 0.43 0.4 0.28 0.27 0.21

𝑉𝑜 ⁄𝑉𝑖𝑛

20 log 𝑉𝑜 ⁄𝑉𝑖𝑛 (dB)

4.7 5.7 5.9 6.3 6.4 6.6 6.7 6.7 6.7 6.7 6.7 6.7 6.6 6.6 6.6 6.4 6.4 6.3 5.9 5.5 5.1 4.3 4 2.8 2.7 2.1

13.44196 15.1175 15.41704 15.98681 16.1236 16.39088 16.5215 16.5215 16.5215 16.5215 16.5215 16.5215 16.39088 16.39088 16.39088 16.1236 16.1236 15.98681 15.41704 14.80725 14.1514 12.66937 12.0412 8.943161 8.627275 6.444386

Frequency Response:

Calculations: Output Impedence, Zout = RC = 6kΩ 𝑟𝑒 =

26 𝑉𝑇 = 26Ω ⁄𝐼 = 𝐶 1

Input Impedence, Zin = 𝑅1 ∥ 𝑅2 ∥ 𝛽𝑟𝑒 = 2.063 k Ω Voltage gain , 𝐴𝑣 = −𝑔𝑚 𝑅𝐶 = −230.76

Inference: The common emitter amplifier was designed, and its frequency response was plotted....