EEE 102
NAME: AMIT MONDOL
ID: 2019-2-80-009
SEC: 02
EXP NO: 07
EXP NAME: An open-ended lab.
DATE OF SUBMISSION: September 18, 2020
Submitted Khairul Alam
to Professor, EEE
OBJECTIVE: The objective of this experiment is to assess students’ skill
on designing and performing demonstration of an open-ended lab.
PROBLEM STATEMENT
Design a common emitter BJT amplifier with the given data and target as
follows
Given data
1. Supply voltage VCC = 15 volt.
2. Transistor has β = 100.
3. Load resistance RL = 2 kΩ.
4. Input signal vin = 10 mV (peak) at 10 kHz.
Target to achieve
1. Input resistance Ri >= 2 kΩ.
2. Voltage gain AV = -50 (V/V)
3. Output resistance R0 <= 4 kΩ.
Circuit Diagram:
Detailed Steps:
1. First, I drew the small signal equivalent circuit.
2. Then I wrote the expression of Input impedance, output impedance
and voltage gain.
3. Then we can see output impedance has less unknown, R0=RC , now let
RC=3.6 < 4 .
4. Since Ve=0 then Vbe = Vin and voltage gain is given , so I can easyly
calculate gm from the voltage gain expression.
5. Now I know gm then I calculate Ic , after calculating Ic then I calculate
IB and IE . I now IB and VT so I calculate rb.
6. Now, I know Ic and Rc then I calculate Vc drop. Then we can calculate
Ve = Vcc-(drop across Rc + Vcc/2 ) .
7. Then I know Ve and IE , I calculate RE.
8. Then I calculate R1 and R2 by using design rule.
9. Now I know R1,R2 and rb then I calculate input Impedance Ri= 2.36
Equipment List: One Q2N2222 npn BJT, One resistor (80.85k), one resistor
(38.27K), one resistors (3.6k), one resistor (2.6k), one resistor (2k),Three
capacitors (10μF), one Vsin source , one voltage source ( 15V), four GND_EARTH
ans Pspice.
Experiment procedure (Pspice):
1. First draw the DC part of the circuit. That is, Q1, R1, R2, RC, RE, and 15-V
Source.
2. Click on the BJT=> Model=>Edit instance model=> and change the value of
bf=125.5. It will give BETADC=100.
3. Use R2= 38.27k. This will give a VCE of 7.5 volt.
4. Run the simulation with bias point calculation only. Check VCE. This should
be approximately 7 volts. If not, change the R2 value and run again.
5. Write the values of VC, VE, and VB.
6. Write beta(dc) from analysis → examine output file.
7. Now add the rest of the components.
8. Set V1 as VSIN. Set its frequency to 10 kHz, amplitude to 10 mV, and VOFF
to 0.
9. Setup simulation to transient. Set stop time to 200 us and step ceiling to 1
us.
10.Simulate the circuit and observe the output. It will be a sine wave.
11.Measure the peak-to-peak values of the output signal and input signal.
12.Observe both the input and output signals together. For better view,
multiply the input by 50. Now measure the phase difference.
13.Observe the current through Vin and measure its p-p value.
14.Measure the peak to peak value of open circuit voltage. To do that, change
the RL value to 100 gigaOhm.
15.Measure the peak to peak value of short circuit current. To do that, change
the RL value to 1 miliOhm.
Input (p-p) voltage = 20 mV
= 20*10^-3 V
Input (p-p) current = 8.11uA
= 8.11*10^-3 mA
input impedance Ri = (Input (p-p) voltage) / (Input (p-p) current)
= (20*10^-3 / 8.11*10^-3)
= 2.46 kΩ
open circuit voltage(p-p) = 2.68 V
short circuit current(p-p) = 776.8 uA
= 776.8*10^-3 mA
The output impedance R0 = open circuit voltage(p-p) / short circuit current(p-p)
= (2.68/776.8*10^-3) kΩ
= 3.45 kΩ
output (p-p) voltage = 988.79mV
= 988.79*10^-3 V
input (p-p) voltage = 20 mV
= 20*10^-3V
The voltage gain Av = output (p-p) / input (p-p)
= (988.79*10^-3 /20*10^-3) V/V
= - 49.43 V/V ( phase difference 180 degree}
Verifying:
Av Ri R0
Calculation -50 2.36 3.6
Simulation -49.43 2.46 3.45
Comment: There is very small differences, which is maybe technical fault.
