Copy of MOSFET CS amplifier

Follow the below steps of analysis for this circuit: 1. Open the switches S1, S2 & S3. 2. Run the DC-OP simulation to obtain the DC values of voltages and currents at the Drain, Source and Gate terminals. This gives you the DC operating point for the MOSFET. 3. Next run a DC-Sweep simulation by sweeping the voltage source V_Supply from 0 V to 15 V. In the grapher window, select to display the graphs of the gate voltage(V_I_Gate), Drain voltage (V_I_Drain) and Drain current (V_I_Drain), deselect all the others. 4. Observe at what voltage the drain current starts to flow. The corresponding gate voltage is the Gate Threshold voltage required to turn ON the MOSFET. Measure the corresponding Source Voltage(V_I_Source) and calculate the gate-source voltage (VGS-threshold). 5. Now close the switch S1 to apply the input signal to the gate. Run the Transient simulation (0-10 ms) and observe the plots of Input and Output signals. Note the signal inversion. Measure the amplitudes of both the signals and calculate the gain (Vout/Vin). This gives you the gain at 1 kHz signal frequency. Convert it into dB by calculating 20log(Vout/Vin). 6. Next run a AC Sweep simulation to see the gain variation with input signal frequency. Verify the value at 1 kHz matches with your calculation in previous step. Note the range of frequencies where the gain is constant. Note the points where the gain reduces by 3 dB, calculate the range. This gives you the 3 dB range. 7. Next close the switch S2 to bypass the source resistor with a 220 uF capacitor. Repeat the observations from step 2 to 6 again. Note that the bypass capacitor does not affect the DC operating point or gate threshold, however note the change in gain. Does it increase or decrease? How does the 3 dB frequency range change? 8. Note that, we have still not connected the load resistor in above analysis. A typical load (for ex. a speaker) can be modelled with a small resistance ~8 ohms. Now close the switch S3 and run the transient simulation. Observe how the gain changes. This is due to the loading effect of the speaker/load. Another output stage with proper impedance needs to be introduced between the drain of the amplifier and the load to avoid it. 9. Set the load resistance R_Load to 10k ohm. Now vary the drain resistance by increasing and decreasing it by 2 times and measuring the corresponding gain for each value by running the transient simulation. How does the gain vary with the drain resistance? 10. Keep the load resistance R_Load to 10k ohm and revert back the drain resistance to original value (4.7k ohm). Now check the output signal by running a transient simulation for different values of input signal amplitudes. Increase it in steps from 10 mV to 100 mV and check the output signal for each case. What do you observe at higher amplitudes? The range of signal amplitudes where the amplifier works without distortion can be found from the transfer characteristics of the MOSFET. It can be found independently using another circuit. Also, note the importance of the input and output coupling capacitors, to prevent the disturbance to the DC operating point of the amplifier. It can also be verified independently using a separate circuit by removing the capacitors and observing the effect on gain, DC biasing and frequency response.