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Analog Electronic Circuits Lab-module1

Module by: Gowra P S. E-mail the author

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:-

Figure 1
Figure 1 (graphics1.wmf)

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:-

  1. The connections are made as shown in the circuit diagram.
  2. Before applying the input signal, the DC conditions are checked by setting VCC = 10V. VCE must be close to ½ VCC ≈ 5V.
  3. Input sinusoidal signal (around 20mV peak to peak ) should be applied using audio signal generator.
  4. Keeping input signal Vin constant, the frequency of the input sine wave is varied from 100hz to 1MHz in suitable steps while measuring the output voltage for different frequencies. The gain of the amplifier is calculated from these values.
  5. Also the gain in db is calculated and tabulated. The graph of frequency versus gain in db is plotted on a semi log sheet.
  6. Bandwidth is calculated from the frequency response. Also gain bandwidth product is computed.

Tabular Column:-

Vi = ---------- mV

Table 1
Frequency (hz) V o A v = V /V i Gain in db= 20log10 V/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

Figure 2
Figure 2 (graphics2.wmf)

  1. DRB is connected as shown in the circuit and let the resistance of DRB be zero.
  2. Input sine wave (20 to 50mV peak –peak) is applied keeping the frequency in the mid band region.
  3. Output voltage Vo is measured.
  4. Resistance on DRB is increased till Vo reduces to half of its value. The DRB value gives the input impedance Zi of an amplifier.

c. To measure output impedance Z o :-

ViVo

Figure 3
Figure 3 (graphics3.wmf)

  1. DRB is connected as shown in the circuit and let the resistance of DRB be high in terms of several kilo ohms or mega ohms.
  2. Input sine wave (20 to 50mV peak –peak) is applied keeping the frequency in the mid band region.
  3. Output voltage Vo is measured.
  4. Resistance on DRB is decreased till Vo reduces to half of its value. The DRB value gives the output impedance Zo of an amplifier.

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:-

Figure 4
Figure 4 (graphics4.wmf)

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 = 1K

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

Table 2
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

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