INTRODUCTION TO MOSFET AND MOSFET INVERTER

Lab#6

Purpose: Our purpose is to study characteristics of MOSFET and understand the working principle of MOSFET inverter.

Parts/Equipment Needed:

1 BS170 n-channel Enhancement type MOSFET

• 1kΩ Resistor

• 500Ω Resistor

• Function Generator

• Oscilloscope

• Breadboard

• Multimeter

• Power Supply

1. MOSFET

The MOSFET will operate in the triode region if V_DS is less than excess gate voltage, that is, if

V_DS<V_GS-V_TR

Conversely, the MOSFET will operate in the constant-current region if V_DS is greater than the excess gate voltage

V_DS>V_GS-V_TR

When V_GS is smaller than the threshold voltage V_TR, the device is said to be in cutoff. In the cutoff condition no current at allcan flow from the drain to the source terminal.

The v-i charactestics of the MOSFET can be summarized by the following equations:

Cutoff region (for V_GS< V_TR) i_D =0

Triode region (V_GS>V_TR and 0< V_DS<V_GS-V_TR ) i_D=K[2(V_GS-V_TR)V_DS-V_DS ² ]

Constant-current region (for V_GS<V_TR and V_DS>V_GS-V_TR ) i_D=K(V_GS-V_TR)²

PRE-LAB

The inverter of figure-1 utilizes an n-channel enhancement-mode MOSFET with parameters K=1mA/V² and V_TR =2V. The Thevenin circuit consists of a single resistor

R_D =500Ω in series with a power supply of value V_DD=7.5V. Find the output of the inverter if Vin=3V. Also find the change in output voltage if Vin is increased to 4V, and plot the Vin-Vout transfer characteristic of the inverter.

Figure-1

Procedure

1.

Build the circuit in figure with the given R_E, V_DD, V_IN values.(V_IN=5Sin(2πx1kxt)+5 V, R_E=2 k,V_DD=15 V).

2.Connect CH1 and CH2 scopes as shown in fig. Observe and record I_D-V_GS graph. (in the X-Y mode,CH1-CH2) (Note that in order to view I_D you have to take the inverse of CH2.)

3.Build the circuit in figure-1 with the given R value but take V_DD =10V.

4.Increase the Vin from 0V to the value Vout becomes constant. Record these values.

Post-lab

1.By using the obtained I_D-V_GS graph for n-channel enhancement-type MOSFET in step 2, calculate V_T.

2. Draw a graph with data that you collect in step 4. (on the x-axis Vin , y-axis Vout)

3. Show the cutoff, constant-current and triode regions on the graph.

4. Find the gain of inverter from the graph.

---