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Activity 3-M. The MOS transistor connected as a diode

Objective:

The purpose of this activity is to investigate the forward and reverse current vs. voltage characteristics of a MOS field effect transistor (NMOS and PMOS) connected as a diode.

Materials:

ADALM2000 Active Learning Module
Solder-less Breadboard
1 - 100Ω Resistor
1 - Small signal enhancement mode NMOS transistor (CD4007 CMOS array)
1 - Small signal enhancement mode PMOS transistor (CD4007 CMOS array)

CD4007 CMOS array pinout

NMOS Directions:

The current vs. voltage characteristics of the gate source of an enhancement mode NMOS transistor can be measured using the ADALM2000 Lab hardware and the following connections. Set up the breadboard with the waveform generator, W1, attached to one end of resistor R1. Also connect scope input 2+ here. Connect the Gate and Drain of M1 to the opposite end of R1 as shown in the diagram. The Source of M1 is connected to Vn (VSS pin 7). Connect scope input 2- and scope input 1+ to the gate - drain node of M1 (pins 6 and 8 for example). (Scope input 1- is best grounded as well to reduce noise pickup). Remember to ensure that both power supply pins (device backgates), VSS pin 7 and VDD pin 14 are connected appropriately to Vn and Vp respectively. All other pins can be left floating. Be sure that the power supplies (Vp and Vn) are turned off while you build your circuit. Once you are sure all your connections are correct then turn on the supplies.

Figure 1 NMOS diode connection diagram

Hardware Setup:

The waveform generator should be configured for a 100 Hz triangle wave with 10 volt amplitude and 0 offset. The differential scope channel 2 (2+, 2-) measures the current in the resistor (and in the transistor). The Single ended input of scope channel 1 (1+) is connected to measure the voltage across the transistor. The current flowing through the transistor is the voltage difference 2+ and 2- divided by the resistor value (100Ω).

Figure 2 NMOS diode Breadboard Circuit

Procedure:

Load the captured data in to Excel and calculate the current. Calculate and plot the current vs. the voltage across the transistor (VGS). No current should flow in the reverse direction. In the forward conduction region, the voltage, current relationship should be quadratic. Also calculate and plot the square root of the current vs. the voltage across the transistor (VGS). Compare the shape of the two plots and comment.

Figure 3 NMOS diode XY plot

Questions:

By plotting the data measured for ID vs VGS, find and report values of VTH and K (W/L).

Are these VTH and K (W/L) values consistent with your measurements on the other two NMOS transistors on the chip?

PMOS Directions:

Repeat the experiment using one of the PMOS devices in the CD4007. The connections are similar and as shown on figure 2 below. You may notice that the polarity of the scope inputs has been reversed in this case. This is so that the direction of the voltage and currents on the scope screen will be similar to the NMOS case. The Source of M1 is connected to Vp (VDD pin 14).Connect scope input 2+ and scope input 1- to the gate - drain node of M1 (pins 6 and 13 for example). Remember to ensure that both supply pins (device backgates), VSS pin 7 and VDD pin 14 are connected appropriately to Vn and Vp respectively. All other pins can be left floating. Be sure that the power supplies (Vp and Vn) are turned off while you build your circuit. Once you are sure all your connections are correct then turn on the supplies.

Figure 4 PMOS diode connection diagram

Hardware Setup:

The waveform generator should be configured for a 100 Hz triangle wave with 10 volt amplitude and 0 offset. The differential scope channel 2 (2+, 2-) measures the current in the resistor (and in the transistor). The Single ended input of scope channel 1 (1-) is connected to measure the voltage across the transistor. The current flowing through the transistor is the voltage difference 2+ and 2- divided by the resistor value (100Ω).

Figure 5 NMOS diode Breadboard Circuit

Procedure:

Load the captured data in to Excel and calculate the current. Calculate and plot the current vs. the voltage across the transistor (VGS). No current should flow in the reverse direction. In the forward conduction region, the voltage, current relationship should be quadratic. Also calculate and plot the square root of the current (ID) vs. the voltage across the transistor (VGS). Compare the shape of the two plots and comment.

Figure 3 NMOS diode XY plot

Questions:

By plotting the data measured for ID vs VGS, find and report values of VTH and K (W/L).

Are these VTH and K (W/L) values consistent with your measurements on the other two PMOS transistors on the chip?

How do the VTH and K (W/L) values for the NMOS and PMOS compare?

Resources:

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university/courses/electronics/electronics-lab-3m.txt · Last modified: 27 Nov 2018 10:24 by amiclaus