1
Lab 4: NMOS at DC (20 points)
1. Objectives
The purpose of this lab is to become familiar with DC operation of NMOS transistor in two
regions: (1) saturation region and (2) triode region
Fig. 1 NMOS iD-VDS characteristics in Triode and Saturation regions: here vGS > Vtn
Fig. 1 shows how an NMOS operates in two different regions: triode and saturation. Recall that
when vDS < vOV, the NMOS is said to be in triode region and when vDS > vOV , it is said to be in saturation
region. In triode region, current iD depends heavily on vDS whereas in the saturation region, iD has very
little dependence on vDS. The property of NMOS in saturation region is important for its use as an
amplifier.
Fig. 2 NMOS circuit for Triode- and Saturation-mode operation
2
4.1 NMOS in Saturation Mode:
1) Design (Use Example 5.6 in the book as a guide)
First we need to determine values of the resistors shown in Fig. 2.
Assume R1 = R2 = 3 MΩ, ID = 1 mA, VD = 10 V, and VDD = 15 V. Use kn = 1.08 mA/V2
What is VG? What is VOV? What is VGS? You will need to look up Vtn from the datasheet
(it may show up as Gate Threshold Voltage or VTH or something like that). You will need
to find VG, VS and VD. Refer to Table 5.1 and Section 5.1.6 in the book.
L1: Find RS and RD.
2) Simulation
Using the values found above, simulate the circuit shown in Fig. 2 (we will use
2N7000TA as NMOS in the experiment. Use 2N7002 if 2N7000TA is not available).
L2: Report the values of VS, VD, VG, and ID. Compare the simulated values with the
calculated values above.
3) Experiment
Assemble the circuit on the breadboard. Using multimeter, measure VS, VD, VG. . Also
measure the values of all the resistors up to 3 significant digits.
L3: Based on the measured values of VS, VD, and the measured values of resistors,
what is the measured values of ID?
L4: How do the measured values compare with simulated values and calculated
values?
You can use the table below to summarize your results.
Table L4: Saturation Mode
Variable
Name
Calculation
Simulation
Experiment
VS
RS
VD
RD
VG
ID
3
4.2 NMOS in Triode Mode:
4) Design
Redesign the circuit for Triode Mode. Assume R1 = R2 = 3 MΩ, ID = 1 mA, VD = 6 V,
VDS = 0.26 V, and VDD = 15 V.
You will have to use equation for Triode region.
What is VG? What is VOV? What is VGS?
L5: Find RS and RD.
5) Simulation
Using the values found above, simulate the circuit shown in Fig. 2.
You may need to adjust the values of RD and RS until you achieve VD ~ 6 V. Verify that
you are still in the triode region (VDS < VOV).
L6: Report the values of VS, VD, VG, and ID. Compare the simulated values with the
calculated values above.
6) Experiment
Assemble the circuit on the breadboard. Using multimeter, measure VS, VD, VG. . You
may need to adjust the values of RD and RS until you achieve VD ~ 6 V. Also measure the
values of all the resistors up to 3 significant digits.
L7: Based on the measured values of VS, VD, and the measured values of resistors,
what is the measured values of ID?
L8: How do the measured values compare with simulated values and calculated
values?
You can use the table below to summarize your results.
Table L9: Triode Mode
Variable
Name
Calculation
Simulation
Experiment
VS
RS
VD
RD
VG
ID