1- Use DC sweep in PSpice to get VI curve for JFET using DC voltage sources for drain-source (sweep from negative to positive values) and gate-source (sweep from 0 to negative values), no resistor is needed. Use the values in figure 6-1 for start.
2- Compute resistance vales for obtained straight lines (VI curves). Use R = 1/slope. Label the calculated resistance and gate-source voltage for each line.
3- Select the most vertical line (highest slope value) to be RJFETON state, and the most horizontal line (slope ~ 0) to be RJFET OFF state. Select the gate-source voltages associated to those states to define voltage limits for control signal (square pulse).
4- Build circuit in figure 6-3 with R1 10 times larger RJFET ON state, use Vpulse (1 Khz, dc 50%) as control signal with levels from part 3, use Vsin (10 Khz) as input signal with amplitude for drain-source voltage from part 1, run transient analysis, plot output signal for 2 complete periods.
5- Repeat part 4 with Vpulse (100 Khz, dc 10%) control signal.
Procedure:
1- Get VI curve for JFET using FET_Resistance.vi, record drain-source voltage values for straight lines obtained.
2- Compute resistance vales for obtained straight lines (VI curves). Use R = 1/slope. Label the calculated resistance and gate-source voltage for each line.
3- Select the most vertical line (highest slope value) to be RJFETON state, and the most horizontal line (slope ~ 0) to be RJFET OFF state. Select the gate-source voltages associated to those states to define voltage limits for control signal (square pulse).
4- Build circuit in figure 6-3 with R1 10 times larger than RJFET ON state, use a DC source as control signal for gate-source (use selected values in part 3 for ON & OFF states), use the function generator (10 Khz) as input signal with Vmax=100mV and Vmin=-100mV for drain-source voltage, capture input and output signals with scopegrab.vi, and register pp voltage values for input and output.
Use an extra function generator to generate a control signal with the JFET on and off voltage levels, a duty cycle of 50% and a frequency of 1Khz. Capture the input and output waveforms using scopegrab.
Change the duty cycle to its minimum value and the frequency to 100Khz. Capture the waveforms using scopegrab.
Analysis:
How would you modify the circuit (you can add componants), so it will work for inputs in the range ±5?
Do the following with the data obtained in the laboratory:
Plot Vout and Vin for the on level. Explain what you are seeing.
Plot Vout and Vin for the off level. Explain the results.
Plot Vout and Vin for the 1Khz control signal. Explain the results.
Plot Vout and Vin for the 10Khz control signal. Explain the results.
