ECE 206: MOSFET Amplifiers

ECE 206: MOSFET Amplifiers
MOSFETs (Metal-Oxide Semiconductor Field
Effect Transistors) are the second major form of
transistor devices besides BJTs. Even though we
did not discuss MOSFETs in ECE 205, we will use
them in ECE 206. A convenient (if simplified) way
to think of a MOSFET is as a BJT, except that the
control happens through the voltage of the gate,
rather than the current of the base as in the BJT.
In this lab, you will characterize the NMOS device provided
(2SK3703). Do this by measuring 𝐼𝐷 as a function of 𝑉𝐷𝑆
and 𝑉𝐺𝑆. The general form of the I-V characteristic should appear
as it does below in Figure 2.
Note that the equations which describe the
“linear region” and the “saturation region” are
complex. Note also that the saturation region
for a MOSFET is different from the saturation
region of a BJT (why is this)?
Prelab Deliverables:
• Draw a figure (based upon Fig. 1) that
shows instrument placement (by specific
instrument name) to collect the 𝐼𝐷, 𝑉𝐷𝑆 and
𝑉𝐺𝑆
• If the units of the Y-Axis in Fig. 2 is in mA,
what is the value of ID when VDS = VGS = 6V?
• List procedures for measuring the DC motor’s power requirement and power dissipated by the
MOSFET amplifier when the motor is on.
References:
• General Description of MOSFET devices:
https://en.wikipedia.org/wiki/MOSFET
http://www.electronics-tutorials.ws/transistor/tran_6.html
• ON Semiconductor 2SK 3703 Datasheet found on ECE 206 website (Resources)
Figure 1: Experimental Setup
Figure 2: Typical N-channel MOSFET (Enhancement Mode) I-V
Challenges:
- Produce a similar plot as with Lab 4.1, this time using a N-channel MOSFET (NMOS) instead of a
BJT. In this case, you should use the 2SK3703 MOSFET and the generic “NMOS” model on
LTSpice. You should right click on this model and populate the parameters – which you can find
in the 2SK3703 datasheet found on the course website.
- Note that multiple values are given for some values (e.g. 𝑅𝐷𝑆(𝑂𝑛)
), in this case, use the
condition where 𝑉𝐺𝑆 = 5𝑉.
• Determine the amplifier circuit’s parasitic power requirement while powering a DC motor,
compare this to the BJT amplifier previously.
Report Deliverables:
• Provide descriptions with accompanying diagrams of your circuits and experimental setup; include
an annotated schematic of your experimental setups by using Fritzing.
• Plot the I-V characteristics for at least 3 𝑉𝐺𝑆 voltages as in Fig 2. Provide enough data points to show
important I-V characteristic features.
- Draw and label the circuit’s linear, saturated, and cutoff operating regions.
- Describe the criteria defining each operating region.
• Have your TA check verify your motor circuit.
• Report the motor power requirement and amplifier power dissipation.
- What impact would the amplifier’s power loss have on your motor’s performance?
- Which device (BJT or MOSFET) is more efficient for controlling the motor?