EL - 250

Advanced Analog Circuits

Lab #3: Common Source JFET Amplifier

Andrew Buettner

March 5, 2003

Objective

The objective of this lab is to determine the characteristics of a JFET, then to use that JFET in an audio amplifier to test it's operation by measuring the output and input voltages to calculate the theoretical and actual gain for a comparison.

Equipment Used

No equipment necessary for this experiment. All data taken from computer simulations.

Procedure

I: Part A

1) Assemble the following circuit:

2) Run the simulation ensuring that the results are similar

3) Set V_GS to .5V and record the results

II: Part B

1) Using the values obtained from part A to determine the V_P for the theoretical JFET

2) Use the value calculated for V_P to calculate I_DSS

3) Using V_GS and the calculated I_DSS calculate I_D

III: Part C

1) Assemble the following circuit:

2) Determine ID, gm, the voltage gain, and the voltage output

IV: Part D

1) Load CSJFAMP.CKT in CircuitMaker©

2) Run the simulation and determine V_out

3) Compare the result with that of part C

Data

1) Table 1: Results from Part A

V_GS	V_RD	I_D
1V	1.832V	1.832mA
.5V	8.362V	8.362mA

2) Table 2: Results from Part B

V_GS	V_P	I_DSS	I_D
1V	-1.44V	19.62mA	1.83mA
.5V	-1.44V	19.62mA	8.36mA

3) Table 3: Results from Part C

V_OUT	I_D	gm	A_V
8.232V	1.968mA	90.6mS	205.8

4) Table 4: Comparison between Part C and Part D results

	Part C:	Part D:	% error:
V_OUT	8.232V	8.050V	2.211%

5) Diagram 1: Schematic, 1 Enlarged View

6) Diagram 2: Schematic 2, Enlarged View

Conclusions

From this lab, it is shown how to use a JFET in an audio amplifier circuit and perform a small signal analysis. I would like to comment that the final voltage on the simulation may not be accurate as the voltmeter and oscilloscope were not giving accurate readings, either that or I was not reading them correctly as this is the first time I've ever used circuit maker. I was able to overcome all other problems as I feel that my calculations are fairly accurate (< 3% error from simulation.)

Attachments

1) Original Lab Handout

2) Original Lab Data

3) Calculations