COLPITTS OSCILLATOR using COMMON EMITTER CONFIGURATION. SIMULATION AND CALCULATION

PROBLEM: 1.Find the Voltage drop at a. Vb Voltage Bias b. Ib Current c. Ie Current d. Ic Current 2.Find the Voltage Gain and r'e 3.Determine the resonant Frequency of the tank circuit Capacitors in Series *Given: Vcc= 28V RC= 1kilo Ohm RB1= 8.2 kilo Ohm RB2= 1.5 Kilo Ohm RE= 1.2 Kilo Ohm Si= 0.7 Volts *Equation: (1. a) by VDP Voltage Divider Principle Vb = 28 Volts *(1.5 Kilo Ohm/ (1.5 Kilo Ohm + 8.2 Kilo Ohm)) Vb= 4.32 Volts approximately equal to The Simulated Value at Vb which is 4.29V (1.b) solving for Ib=? Ib#1= (Vcc-Vb)/ 8.2 Kilo Ohm Ib#1= 2.887mA approximately 2.89mA Ib#2= 4.32Volts/1.5Kilo Ohm Ib#2= 2.88mA (1.c) Solving for Ie=? Ie= Vb - 0.7Volts / (1.2 Kilo Ohm ) Ie= 3.016mA approximately equal to the simulated value at 2.95mA (1.d) Vbe= Vb-Ve = 4.32V-(0.7)= 3.62V Vcc-Vbe+(0.7)=Vc Vc=28V- 3.62V+0.7V = 25.08Volts or approximately equal to 25.1 Volts therefore: Ic= Vcc-Vc/Rc = (28-25.1) Volts/1 Kilo Ohm Ic= 2.9mA 2. Equation of Voltage Gain and r"e Voltage gain denotes as AV where AV= Rc/Re Therefore: Av= Rc/Re = 1 Kilo Ohm/ 1.2 Kilo Ohm Av=0.8333 (will not oscillate) because it is not greater than 1 Finding the r'e from the equation at room temperature: r'e= 26mV/Ie therefore: r'e= 26mV/ 3.016mA r'e=26mV / 3.016mA r'e=8.62 ohm plugging this value of r'e to the equation of Voltage Gain Av= Rc/r'e Av= 1 Kilo Ohm/ 8.62 Ohm Av= 116 ; Voltage gain with internal resistance in emmitter diode r'e Therefore this Oscillator will Oscillate due to Av > 1 3. Determine the resonant Frequency of the tank circuit Capacitors in Series. C1= 4.7 nano Farad C2= 47 nano Farad Finding fr=1/2π(L Ctotal) ̂ 0.5 Where Ct= C1*C2/C1+C2 Ct=4.27 nano farad, plug in this value to fr=1/2π(L Ctotal) ̂ 0.5 that gives resonant frequency fr= 1/2π(L *4.27nF) ̂ 0.5 = 76.995Khz or 77Khz *Follow this procedure below * to see the signal waveform. Toggle the 2 switches from the 1 micro farad to the base of the transistor and the tank circuit to the collector side of the transistor for the feedback, then play the button and wait for 5 to 10 seconds before it appears. * Observe the frequency that flashes on the simulation screen for about 1 to 2 minutes from a varying frequency of 73Khz to 74Khz. * That gives you a slight and almost negligible difference of 2 to 3 KHz from the calculated value of resonating frequency (fr).

published 4 years ago