Procedure

Apparatus

Transistors, resistors, capacitors, inductance coil, dc power supply, C.R.O.

1. Designing

Selection of Transistor: Use a high-frequency NPN transistor such as BF195.

Component Values:
L = 10 μH
V_CE = 0.5 × V_CC
V_RE = V_E = 0.1 × V_CC
V_RC = V_C = 0.4 × V_CC

Applying KVL for the Output Loop

V_CC = I_C R_C + V_CE + I_E R_E
      = I_C R_C + V_CE + V_E

Therefore:

$$R_C=\frac{V_{CC}-V_{CE}-V_{E}}{I_C}$$

$V_E=I_ER_E \approx I_CR_E$

There for

$$R_E=\frac{V_E}{I_E}$$

Let V_CC = 12V, β = 60 and I_C = 1mA

Applying KVL for the Output Loop

V_CC = I_CR_C + V_CE + I_ER_E = I_CR_C + V_CE + V_E

Therefore:

$$R_E = \frac{V_{CC} - V_{CE} - V_E}{I_C} \approx 4.7k\,\Omega$$

$$V_E = I_E R_E \approx I_C R_E$$

$$R_E = \frac{V_E}{I_C} = 1.2\,k\,\Omega$$

$$I_{R1} \approx 21 I_B \quad \text{and} \quad I_{R2} = 20 I_B$$

$$\text{i.e.} \quad R_2 \leq \frac{1}{10} \beta R_E \approx 7.5\,k\Omega$$

$$V_{BB} = \frac{R_2}{R_1 + R_2} V_{CC} = V_{BE} + V_E = 0.7 + 1.2 = 1.9\,V$$

$$R_1 \approx 39\,k\Omega$$

Design of Feedback Network

Selection of capacitors: All capacitor values may be taken as 1μF.

Required frequency of oscillation: f = 1000 KHz

Let L = 10μH

Frequency formula:
$$f = \frac{1}{2\pi\sqrt{\frac{L C_{1} C_{2}}{C_{1} + C_{2}}}}$$

Effective capacitor C_eq = 2.5 nF

Therefore, C = 5 nF

Result

Amplitude and frequency of sine wave from Colpitts Oscillator = ……….. V, ……….. Hz.

Procedure for simulator

1. Begin by arranging the components on the virtual breadboard as shown in Animation 1. Refer to the visual guide carefully to place each component in its correct position.


2. To connect the components, click on one end of the wire and then click on the corresponding point on the breadboard to complete the connection. Repeat this step to interconnect all necessary components.


3. Follow the connection diagram to ensure the circuit is completed correctly. Double-check that all connections are made as shown in the schematic.
4. Once the circuit is fully connected, click the "Show CRO" button in the simulator interface. This will display the waveform output on the virtual Cathode Ray Oscilloscope (CRO).

To Change the Component Value

1. Select the component whose value you want to modify by clicking on it within the simulator.
2. Use the slider on the right-hand side of the simulator to adjust the value (e.g., resistance, capacitance) as needed for the experiment.