Lab #7
Follow the instruction and procedures in the Student Manual, unless specified differently
in this note.
Reading:
p.142 – 162 in SM
Ch. 3.01 – 3.10 in AE
Lab #7
7-1 Follow the instruction. Make a semi-log plot of ID vs VGS curve based on your
measurements. Measure IDSS and VP for 3 – 4 samples of 2N5485. Pick one of the FET’s
in 7-2 and 7-3 and use the specific numbers that you measured for the sample. Plot the ID
– (VGS-VP) curve for the sample you chose (linear plot) and confirm its quadratic nature.
7-2 Follow the instruction (measure ID and VDS for 20 Ohm < R < 200k Ohm). Identify a
region for a good current source. Skip 7-2 (b).
7-3 Follow the instruction (read p.159 carefully). You measure gm from your experiment.
You can find the manufacturer’s range of gm for the 2N5485 on p.592 of the lab manual.
Compare your value with the manufacturer’s one, considering the fact that the
manufacturer’s value is for VGS = 0. Skip 7-3 (c).
7-4 Follow the instruction. In (b), explain why adding ½ vDS would improve the situation.
For (c), conduct simulation and experiment. Use around 1 KHz 2 Vpp for message
(modulation) and 10KHz 2 Vpp for carrier (vin). See the instruction for the simulation.
7-4c Amplitude Modulation
The figure above is the schematic for a Amplitude
Modulator circuit.
Hints: Vmessage and Vcarrier are sinusoidal voltages
(use VSIN not VAC) therefore you will need to
specify the amplitude, the offset (0) and the frequency.
The analysis type for this simulation is transient. The
final time is around 20 periods of the carrier
frequency.
You can replace the potentiometer with regular
voltage dividing network composed of two resistors.
Caution: 1 MOhm resistor should be 1 MEG in
simulation (not 1 M).
Part 1: Simulate the circuit with the signals suggested
in the instruction.
Part 2: What happens to the AM signal as you change
the potentiometer ratio from 0.1 to 0.9?