EE 2212

EXPERIMENT 6

2 March 2017

MOSFET I-V Characteristics

Report Due: 16 March 2017

PURPOSE

To measure the I-V characteristics of an N-channel MOSFET on the CD 4007 array

COMPONENTS

Ø CD4007 MOSFET array

PRELAB

Prepare a detailed circuit diagrams in your notebook of how you will connect an NMOS for measuring the I-V curves and how you will connect the inverter circuits. Study the material in Chapter 4. A complete manufacturer’s data sheet has been posted as a pdf file on the class WEB page.

The device you will use throughout this experiment and Experiment 7 is a CD4007B Transistor array. It contains three N-channel and three P-channel devices connected as shown. Detailed schematic diagrams and pinouts are available on the data sheet and also given below, Figure 6.1. Please use care when working with these chips. They are very susceptible to excessive voltage and ESD (Electro-Static Damage). Do not exceed the experiment settings in an attempt to make your experiment work. The pin configuration is given in Figure 5.1. Note that you will be using the CD4007B which have a lower maximum voltage rating than the CD4007UB. The diagrams are the same for both the “B” and “UB” suffix devices. Avoid exposing the chip to ESD (electrostatic damage). This time of the year often has low relative humidities which make ESD more of an issue. Do not exceed the V_DD maximums!!!

Study the I-V curves provided in the data sheets so that you have some idea of what to expect. Also study the chip circuit diagram. You should be able to identify the operation and function of all of the individual devices. Observe the input protection circuitry that we will discuss in Wednesday’s class.

Figure 6.1 Pin Configuration of CD4007.

Warning: Pin 14 should always be connected to the most positive dc voltage in the circuit. Pin 7 will always be connected to the most negative dc voltage in the circuit

(or else )!!!

PROCEDURE

I-V Characteristic of an N-channel MOSFET

Ø Connect the circuit shown in Figure 6.2. Use the NMOS connected to pins 6, 7, and 8. Remember to connect pin 14 also to the +VDD supply. Pin 7 is shown connected to ground. Although you can use the built-in mA meter on the power supply to measure I_D , a better way yielding better accuracy is to measure current by measuring the voltage drop across a 100 Ω resistor connected from Pins 8 and 14 and realizing that I_D = V_{(across the resistor})/100Ω

Ø Do not use the digital multimeter to measure current because of the hassle in replacing the internal fuse. Use the voltage readout on the power supply as you sweep V_DD from 0 to 10 volts for each value of VGS from 0 to 6 volts in 1-volt increments. Measure VDS and ID for each value of VGS using the multimeter. Note that V_T is in the 1 to 2 volt range. Refer to the data sheets where similar curves are illustrated.

Figure 6.2 I_D-V_DS As A Function of V_GS Characteristic Measurement For an NMOS

Ø Note that you should keep below I_D = 10mA; since this is the maximum rated value for this chip, consequently you may not be able to use all values of V_GS depending upon your chip. Plot data as you proceed.

Ø Using an EXCEL spread sheet and extracting graphs from the spread sheet is a good way to display and understand the data.

Ø The CD 4007 is unforgiving for ESD and over voltage and over current.

Ø Plot your data and use a linear regression (least squares fit) to extract values for VTO, LAMBDA, and KP and develop a SPICE model that compares well with your measured curves. An EXCEL spread sheet works well and yields nice graphs. The objective is to obtain I_D versus V_DS for several different values of V_GS. Look at Figures 5 and 8 on the CD 4007 data sheet as a guide as to what to expect. You will have to assume W/L=1 because you do not know the actual values of W and L and then adjust KP accordingly. This model development from your parameter extractions should be included in your report. Develop a Shichman-Hodges model equation for your NMOS.

Ø Observe that SPICE syntax for K_n^’ (for an NMOS) and K_p^’ (for a PMOS) is KP independent whether you are modeling an NMOS or PMOS. Refer to Table 4.2 from the text; also on the EE 2212 WEB page. We will do more with notation in Wednesday’s class.

Now to assist with your mathematics skills:

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