Design of Single Stage Transistor Amplifier and Colpitt's Oscillator

Design of Single Stage Transistor Amplfier and RF Oscillator

Diagram

Design parameters

Transistor available = 2 SC 828 ( general purpose low power )

b = 200 f_T = 400 MHz

V_cc = 12 VDC

V_ce (quiescent) = 6 V V_E = 0.5 V

I_E = I_C = 0.5 mA R_E = V_E / I_E = 0.5 / 0.5 = 1 k ohm

R_C = (V_cc - V_c ) / I_C = (12 – 6) / 0.5 = 12 k ohm

I_B = I_C / b = 0.5 / 200 = 2.5 uA

I _PD >> I_B = 40 x I_B = 0.1 mA

R₁ = ( V_CC - V_B ) / I_PD = (12 – 1.1 ) / 0.1 = 109 k ohm

R₂ = V_B / I_PD = 1.1 / 0.1 = 11 k ohm

r_e’ = 25 mV/ I_C = 25 x 10^-3 / 0.5 x 10^-3 = 50 ohm

A_{v (max)} = RC / r_e’ = 12000 / 50 = 240

r_b = b r_e’ = 200 x 50 = 10000 = 10 k ohm

r_in = r_b || R1 || R2 = 5.0 k ohm

r_s = 1k then V / V_s = r_in / ( r_in + r_s ) = 5 / 6 = 0.8

A_v = A_vmax x V / V_S = 190

Design of Colpitts L-C oscillator

Coil design

Length ( l ) = 6 cm = 6 x 10^-2 m

Diameter = 1 cm Radius ( r ) = 5.0 x 10^-3 m

No of Turns ( N ) = 100

Inductance ( L ) = u_o N² p r² / l = 2.0 x 10^-6 H

Capacitors to be used = 3.3 nF

Since 2 capacitors are in series total capacity (Ct) = 3.3 / 2 = 1.65 nF

Operating frequency ( f ) = ( 4 p² x L x Ct ) ^-1/2

f = 2.8 MHz

By-pass Capacitor for R_E ( C_E ) >> 1 / 2 p f R_E = 200 / ( 2 p x 2.88 x 10⁶ x 1000 ) = 10 nF

Actual components to be used

R_c = 10 k ohm R_E = 1 k ohm R₁ = 100 k ohm R₂ = 10 k ohm

C_E = 10 nF

Observations

Vc = Vb =

VE =

f =

Amplitude Modulation

Note1: p in some relations is Greek pi = 3.14

Note2: Information given without any liability.

Fayyaz Mahmood

Design of a Bistable Multivibrator