EE 3113, Lab #7 Pre-lab. Pre-lab due start of class on first day of the lab.

Reading SM: Class 7, Lab 7Your Electronic Circuits I text will have sections on junction field-effect transistors (JFET’s) and their circuits if youwant some background information.

Section 7-1 1. Suppose that a JFET has IDSS = 6mA and pinch-off voltage VP = −3V . The JFET is currently biasedto a drain current of ID = 2mA. Estimate the transconductance gm of the transistor at ID = 2mA.

Section 7-2 OMIT THIS SECTION.

Section 7-3 1. Part (a) Simple Follower:

(a) Suppose that you have a source follower as in Figure L7.5. If the gain is estimated to be +0.6, estimate thevalue of transconductance gm for this transistor. (Hint: Consider Figure L7.6.)

2. Part (b) Follower with Current Source Load: OMIT THIS SUBSECTION.

3. Part (c) Matched-FET Follower: OMIT THIS SUBSECTION.

Section 7-4 No problems.

EE 3113, Lab #7 Post-lab.

Section 7-1 1. Measure IDSS and VP for two 2N5485 JFET’s. Note that the values may be quite different between thetwo parts, especially if they come from different manufacturing lots.

2. Choose one of the JFET’s and take enough ID versus VGS data to make a nice semi-log plot. (TYPO: The StudentManual refers to the “Text’s Figure 3.15” but it should say “Text’s Figure 3.8.”) Include a similar plot in yourreport.

3. Estimate gm at VGS = 0 for the JFET you chose above using gm = 2√(kID) or gm = 2k(VGS − VP ), first

estimating k from IDSS = k(VP )2.

Section 7-2 OMIT THIS SECTION.

Section 7-3 1. Part (a) Simple Follower:

(a) Take an input/output screenshot while driving the follower with a 1kHz sine wave with the peak-to-peakmeasurements enabled. Calculate the gain. Use these measurements to infer a value for gm. (Hint: ConsiderFigure L7.6.) (Omit that section of part(a) described on page 159.)

2. Part (b) Follower with Current Source Load: OMIT THIS SUBSECTION.

3. Part (c) Matched-FET Follower: OMIT THIS SUBSECTION.

Section 7-4 1. Part (a) Uncompensated Attenuator:

(a) Drive the circuit with a 0.4Vpp triangle wave input and observe the output as you vary the potentiometer.Take an input/output screenshot at some mid-range value of attenuation.

(b) Now drive the circuit with a 1Vpp triangle wave input and take an input/output screenshot. Compare thedistortion in the two screenshots.

2. Part (b) Compensated Attenuator:

(a) Drive the circuit with a 1Vpp triangle wave input and observe the output as you vary the potentiometer. Takean input/output screenshot. Has the distortion been improved compared to the uncompensated attenuator?

3. Part (c) Amplitude Modulation and Part (d) AM Radio: We will combine these two sections. (This is theinstructor’s favorite lab section.)

(a) You will need a second function generator, which the instructor will provide. Connect the output of thisfunction generator to the BNC1 connection on the ELVIS board using your BNC cable. Build the circuit ofFigure L7.14. (This requires only the addition of a 1 microfarad capacitor or bigger and a short wire antenna.)Wire BNC1- to Ground and connect BNC1+ to vin on your circuit. Connect FUNC OUT to vmod on yourcircuit.

(b) Use the scope to adjust the amplitude of vin to be less than 1Vpp, and set its frequency to as close to 1MHzas possible. Use the ELVIS Function Generator to set vmod to about 1kHz and 0.2V in amplitude. Use yourBNC-to-grabber cable to observe vmod on one channel of the scope and use the probe to observe the outputnode out on the other channel. Trigger on vmod.

(c) When you have the function generators set up, call the instructor. The instructor will bring an AM radioreceiver to listen to your radio signal. Take a screenshot of the modulated output.