Summary: This module includes amplifier and oscillator circuits
Experiment No.1
RC Coupled Amplifier
AIM: Wiring of RC coupled single stage (a) BJT and (b) FET amplifier and determination of gain, frequency response, Input and Output impedances.
a. BJT Amplifier :-
Components :- Resistors, Capacitors, Audio Signal Generator(ASG), 0-30V DC Regulated Power Supply (RPS), Cathode Ray Oscilloscope (CRO) with probes, SL100 Transistor, Decade Resistance Box (DRB), Multimeter, Connecting Wires and Board.
Circuit Diagram:-
RE = 470Ω
Rc = 2.2.KΩ
R1 = 12KΩ
R2 = 2.2KΩ
CE = 47µF
Cc = 1µF OR 0.1µF
Design:-
a. To find R E :-
Let VCC = 10V, IE = IC = 2mA
β = 100 (for SL100)
VCC
Choose VCE = ------- = 5 V
2
1
VRE = ------ VCC = 1V
10
But VRE = IERE
VRE 1
RE = ------- = ------------ = 500Ω (Select 470Ω)
IE 2 X 10-3
b. To find R C :-
1
Choose VCE = ------- VCC = 5 V
2
Applying KVL to the output loop
VCC = VRC+VRE+VCE
VRC = VCC - VRE - VCE = 10 - 1 - 5 = 4V
RC = VRC/IC = 2KΩ (Select 2.2KΩ)
c. To find R 1 & R 2 :-
Stability factor ‘S’ is given by,
1+ β
S = -------------
β. RE
1+ --------
Rth+RE
Assuming S=5 and substituting for RE, β and S in the above equation we get
Rth =1.9KΩ --------- (1)
By applying KVL to the input loop,
VR2 = VBE+VRE = 0.6+1 = 1.6V
VCC
Also Vth = R2 -------------
R1 + R2
R2
= ----------- = 0.16 ------------ (2)
R1 + R2
From equations (1) and (2), we get R1 and R2 as,
R1 = 12.KΩ (Select 12KΩ)
R2 = 2.3KΩ (Select 2.2KΩ)
d. To find by pass capacitor C E :-
XCE = 0.1RE = 47Ω
1
CE = --------- = 33.87µF (Select 47 µF)
2πXCE
PROCEDURE :-
a. To get frequency response:-
Tabular Column:-
Vi = ---------- mV
| Frequency (hz) | V o | A v = V o /V i | Gain in db= 20log10 Vo/Vi |
| 100Hz1MHz |
Frequency Response Curve:-
Mid freq. region
3dbBandwidthf2Frequency in HzGain in dbf1Low freq. regionHigh freq. Region
b. To measure input impedance Z i :-
ViVo
c. To measure output impedance Z o :-
ViVo
Results:-
a. Band width (BW) = --------- Hz
b. Midband gain = Amid = ---------------
c. Gain Bandwidth Product = BW X Amid = ------------------
d. Input Impedance = ---------Ω
e. Output impedance = -------- Ω
b. FET Amplifier:-
Circuit Diagram:-
Design :-
From data sheet of BFW10/11
IDSS = 10mA
VP = -3V or -4V
Let ID = 2mA
a. To find R S :-
From equation for current
ID = IDSS (1 – Vgs/Vp)2
ID/IDSS = (1 - Vgs/Vp)2
Substituting for ID, IDSS andVP, we get
Vgs = - 1.65V
Vgs = IDRS
RS = Vgs/ID = 0.820KΩ = 820Ω
Choose RS = 1KΩ
b. To find R G :-
Igs RG = Vgs
RG = Vgs/Igs = 1.65/1µA = 1.65MΩ
c. To find R D :-
Applying KVL
VDD = ID RD + IDRS +VDS
VDD – VDS – IDRS
RD = ----------------------------
ID
10 – 5 – 2
= --------------------- = 1.5KΩ
2
Let RD = 1.5KΩ
d. To find C S and C C :-
Let f = 100Khz
Xcs = 1/100 RS = 1000/100 = 10Ω
1
Xcs = ---------------
2πfCs
1
Cs = ----------------------------- = 0.15µF (Select 0.22µF)
2πX100X103 X 10Ω
PROCEDURE:-
Same as BJT amplifier. VDS should be ½ VDD ≈ 5V as DC Condition.
Tabular Column:-
Vi = ----------------- mV
| Frequency | V o | A V = V o /V i | Gain in db = 20 log 10 V o /V i |
| 100hz 1Mhz |
Results:-
a. Band width (BW) = --------- Hz
b. Midband gain = Amid = ---------------
c. Gain Bandwidth Product = BW X Amid = ------------------
d. Input Impedance = ---------Ω
e. Output impedance = -------- Ω