Complementos de Electrónica
2024/2025
Trabalho Laboratorial nº 1
NMOS I-V Characteristics
(See Sections 5.1-5.2, p. 248 of Sedra/Smith 7th ed)
Part 1: Simulation report must be sent before beginning the lab work
Part 2 and Part 3 report should be sent by email until one week after the lab class.
OBJECTIVES:
To study NMOS transistor I-V curves by:
− Simulating a transistor to investigate the drain current vs. gate-to-source voltage and drain-to-source
voltage.
− Implementing a circuit and taking measurements of the I D vs. VGS and ID vs. VDS curves.
− Extracting values of kn, Vtn and λn.
MATERIALS:
• Laboratory setup, including breadboard
• 1 enhancement-type NMOS transistor (2N7000)
• Several wires
Note: read the data sheet of the transistor carefully. Notice the continuous maximum drain current of 200 mA
that should not be exceeded during all experimental work.
PART 1: SIMULATION
Consider the circuit in Figure 1. Enter the circuit into your simulator's schematic editor, applying DC voltage
supplies to the gate and drain of the transistor.
Figure 1: Transistor measurement circuit. Related to Table 5.1 in S&S.
ID vs. VGS
While setting VDS to a constant value of 5 V, sweep the gate voltage from 0 V to 5 V in increments of 0.1 V. Plot
a curve of I D vs. VGS· At what value of VGS does the current turn on?
Note: The quickest way of doing this, is by using Multisim analysis tools, namely “DC sweep” available on
Simulate, Analyses menu. It is necessary to select the input variable (Analysis Parameter - VGS) and the output
variable, which is I D or the current given by VDS source. The DC sweep analysis produces the graph of the output
variable as function of the input variable.
ID vs. VDS
For three values of VGS (2.5 V, 2.8 V, and 3.2 V), sweep the drain voltage from 0 V to 5 V in increments of 0.1
V. Plot the curves for I D vs. VDS onto a single graph, clearly indicating the value of V GS next to each curve.
Note: Again, the quickest way of doing this, is by using Multisim analysis tools, namely “DC sweep”.
PART 2: MEASUREMENTS
Assemble the circuit from Figure 1, using a power supply to generate the DC voltages. Do not exceed the
absolute maximum ratings of the transistor (maximum continuous I D current). Take measurements until you
reach a value close to it.
You will need to measure voltage. You can use the digital oscilloscope and set it to make the measurements.
ID vs. VGS
While setting VDS to a constant value of 4 V, sweep the gate voltage in small increments from 0 V (say 0.2 V
increments), and measure the drain current using the amperemeter. Plot a curve of I D vs. VGS. For which
value of VGS does the NMOS turn on?
ID vs. VDS
For three values of VGS (2.5 V, 2.8 V, and 3.2 V), sweep the drain voltage in small increments from 0 V, and
measure the drain current using the amperemeter. Plot the curves for ID vs. VDS onto a single graph, clearly
indicating the value of VGS next to each curve.
Diode-connected transistor
Build the circuit of Figure 2. Notice that the transistor is always in saturation since V GS = VDS, that is, VDS is
always VDS > VGS – Vt.
Figure 2: Diode-connected transistor.
Vary the gate voltage (VGS = VDS) in small steps from 0 V and record the corresponding drain current I D.
PART 3: POST-MEASUREMENT EXERCISE
Simulation vs. measurement
What are the main differences between your simulated and measured curves? Can you explain the
differences?
Parameter extraction
(1) Threshold voltage, V tn, and MOSFET transconductance parameter, k n
Plot the ID vs. VGS curve for the diode-connected transistor. Also, calculate the square root of I D and plot the
1
√ 𝐼𝐷 vs. VGS relationship, that is √𝐼𝐷 = √ 𝑘𝑛 (𝑣𝐺𝑆 − 𝑉𝑡 ). From the intersection with the horizontal axis extract
2
Vtn, and from the slope calculate kn.
Using your extracted values of Vtn and kn, plot a curve of ID vs. VGS, using the saturation model, and compare
with your simulated and measured curves. Are there any differences? Can you explain the differences?
(3) Early voltage, V A
Based on your measured ID vs. VDS curves for a saturated transistor, extract the Early voltage V A. Does VA change
significantly for each value of VGS? What is the average value of VA? Based on your average value of VA, calculate
1
𝜆𝑛 = .
𝑉𝐴
Repeat Steps 1 to 3 for your measured results.
Summarize your results in the following table.
MEASURED
Vtn [V]
kn [mA/V2]
λn [V-1]
NOTE: Details on the PSpice models used by Multisim can be obtained directly from Multisim:
Menu Reports → Component Detail Report → Detail Report button.
