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EEET2097 Electronic Circuits EEET2097 Electronic Circuits Workshop 1 (Weeks 2-3) MOSFET CIRCUITS Special Note: due to the impact of COVID-19, in this experiment you will do theoretical analysis and simulations. You will also watch videos of circuit implementation and measurement and be provided with the measurement results. Based on the measurement videos and provided data, you will do analysis and discussions. 1. AIMS (i) Study input and output characteristics of MOSFETs (ii) Understand the current-voltage (I-V) curve of MOSFETs (iii) Design a MOSFET amplifier, observe its small signal operation and simulate it using NI Multisim 2. INTRODUCTION 2.1 MOSFET MOSFET’s are now the centrepiece of all electronic circuits. It is important to understand how they operate, learn about their governing equations, know how to bias them and study how to use them for the amplification of signals or switching. Figure 1 Circuit symbol for N-MOSFET. A metal-oxide-semiconductor field-effect transistor (MOSFET) is a three-terminal device that can be used as a switch (e.g. in digital circuits) or as an amplifier (e.g. in analogue circuits). The three terminals are referred to as the Source, Gate, and Drain. The MOSFET also has a Body terminal, which is usually tied to the source terminal (so that VBS = 0 volts) in discrete transistors. Current flow between the source and drain terminals is controlled by the voltage VGS applied between the gate and source EEET2097 Electronic Circuits terminals. If the gate-to-source voltage VGS is less than the threshold voltage value Vt, no current can flow between the source and the drain and the transistor is OFF. If VGS > Vt, then current can flow between the source and the drain. The circuit symbol for an n-channel enhancement-mode (Vt > 0 Volts) MOSFET is shown in Figure 1, along with the terminal current reference directions. MOSFET current-voltage (iD-vDS) characteristics (i) Cut-off region The device is in the cut-off region when vGS < vt="" (ii)="" triode="" region="" the="" device="" is="" in="" the="" triode="" region="" when="" vgs="">Vt and vDS is small (it means vDS < vgs="" –="" vt="" or="" vd="">< vg="" –="" vt)="" where="" w="" is="" the="" channel="" width="" and="" l="" is="" the="" channel="" length.="" (iii)="" saturation="" region="" the="" device="" is="" in="" the="" saturation="" region="" when="" vgs=""> Vt and vDS is large (it means vDS > vGS – Vt or vD > vG – Vt) 2.2 NI Multisim Multisim is a powerful schematic capture and simulation environment that engineers use to simulate electronic circuits. We will use Multisim in EEET2097 for circuit simulations. Please refer to the additional “Multisim Tutorial” document for more details about this simulation tool. In general, there are two versions of Multisim available to us: • The desktop version – NI Multisim 14.1: this is the full version with comprehensive component libraries. You can access it via RMIT myDesktop; • The online version – NI Multisim Live: this is the lite version with relatively limited functions and component libraries. You can access it directly at https://www.multisim.com/. It is required to use the full version NI Multisim 14.1 for circuit simulations in this course. In the “Multisim Tutorial”, we use the transient analysis as an example to view the time domain waveform of signals. In this course, we will mainly use three simulation modes, which can be selected at Simulate » Analysis and Simulation. Here we provide the general description and guideline on the three simulation modes: • DC Operating Point: this is used to simulate the DC currents and voltages of an electronic circuit for the bias analysis. You can use “Multimeter” to measure the DC current and voltage. The Multimeter should be connected in shunt (parallel) when measuring the voltage, and in series when measuring the current. EEET2097 Electronic Circuits • Transient: this is used together with AC input signals to analyse the time domain behaviour of the circuit. For example, to analyse the saturation behaviour of op-amp, the transient analysis can be used to monitor the distorted output waveform. Typically, the simulation output of transient analysis can be viewed using the oscilloscope. • AC Sweep: this is also used to analyse the AC behaviour of an electronic circuit. Different from the transient analysis, AC sweep provides the analysis in the frequency domain (e.g., gain v.s. signal frequency). For example, to analyse the frequency roll-off of a MOSFET amplifier, the AC sweep analysis can be used to find the low-frequency and high-frequency break points. The Table 1 below describes the Frequency Parameters tab in the AC sweep analysis. Table 1 3. WORKSHOP PROCEDURE 3.1 In this part, we will use measurements to understand the characteristics of the MOSFET that we will use in this workshop. The model of the MOSFET is ZVN2110A, which is a NMOS transistor. The datasheet is available on the Canvas site (workshop 1 page). The measurement setup that we use is shown in Fig. 2 below. As shown in the measurement video, A DC power supply VDC is connected to the drain of the transistor. A 10 MΩ resistor is connected between the gate and drain terminals, so that the MOSFET is always kept in the saturation region. The source terminal is grounded. VDC is changed from 0 to 2.5 V in 0.1 V increment, and a multimeter is used to measure the drain current at different voltage levels. The measurement results (?? ?. ?. ???) are shown in Table 2. Figure 2 Circuit used for the current-voltage measurement. EEET2097 Electronic Circuits 3.1.1 From the measurement results, what is Vt of the MOSFET? Compare Vt with the datasheet value. 3.1.2 From the measurement results, what is the ?? ′ ( ? ? ) value of MOSFET? Since the transistor is in the saturation mode, you can use the Equation (2) for calculation. 3.1.3 Discuss why the step 3.1 is important in practical electronic circuits. Table 2 Voltage Current Voltage Current Voltage Current 0 V 0.002 uA 0.9 V 0.003 uA 1.8 V 171.86 uA 0.1 V 0.002 uA 1.0 V 0.003 uA 1.9 V 1.078 mA 0.2 V 0.002 uA 1.1 V 0.016 uA 2.0 V 2.404 mA 0.3 V 0.002 uA 1.2 V 0.049 uA 2.1 V 11.513 mA 0.4 V 0.002 uA 1.3 V 0.097 uA 2.2 V 16.737 mA 0.5 V 0.002 uA 1.4 V 0.981 uA 2.3 V 20.381 mA 0.6 V 0.002 uA 1.5 V 1.754 uA 2.4 V 31.167 mA 0.7 V 0.002 uA 1.6 V 21.902 uA 2.5 V 62.306 mA 0.8 V 0.002 uA 1.7 V 58.915 uA 3.2 Build the circuit shown in Fig. 2 in NI Multisim. In the simulation, use the component “ZVN2106A”, which is similar to ZVN2110A used in the measurement. You can search for the component in Place » Component. We also need to change the parameters of the transistor in NI Multisim according to the measured characteristics. To do this, double click the MOSFET component, and then select Edit Model. The parameters we need to change here are all included in “.MODEL MN2106 NMOS”. Kp is the ?? ′ ( ? ? ) in Equation (2), and “Vto” is the Vt. When changing parameters, you can adjust “Kp” and “Vto” according to measurement results you obtained in step 3.1. 3.2.1 Simulate ?? ?. ?. ??? (change VDC from 0 to 2.5 V in 0.1 V increment). Compare and discuss the simulation results v.s. the measurement results. Figure 3 Circuit used for the current-voltage measurement. EEET2097 Electronic Circuits 3.3 To further understand the output characteristics of the MOSFET, we use the circuit shown in Fig. 3 to measure the drain current at different drain voltages. A gate voltage is applied to the transistor as well. As shown in the measurement video, we start with a gate voltage of 1 V (i.e., ??? = 1 ?) and change the drain voltage (i.e., ???) from 0 to 5 V in 0.5 V increment. We measure the drain current. We then change the gate voltage from 1 V to 2.5 V in 0.5 V increment and repeat the step above for each gate voltage. The recorded measurement results (?? ?. ?. ???) are shown in Table 3. 3.3.1 Plot the output I-V curves (i.e., ?? v. s. ???) for different gate voltages. Show all curves in one graph. Identify the Triode and Saturation regions. Table 3 VGG =1 V VGG=1.5V VGG=2V VGG=2.5V VDD ID VDD ID VDD ID VDD ID 0V 0.002uA 0V 0.95uA 0V 4.78 uA 0V 4.91uA 0.5V 0.002uA 0.5V 5.24uA 0.5V 1.68 mA 0.5V 37.76mA 1V 0.002uA 1V 5.27uA 1V 1.71mA 1V 47.21mA 1.5V 0.002uA 1.5V 5.29uA 1.5V 1.72mA 1.5V 49.27mA 2V 0.003uA 2V 5.30uA 2V 1.73mA 2V 51.37mA 2.5V 0.003uA 2.5V 5.31uA 2.5V 1.75mA 2.5V 53.17mA 3V 0.005uA 3V 5.32uA 3V 1.76mA 3V 55.21mA 3.5V 0.005uA 3.5V 5.32uA 3.5V 1.77mA 3.5V 57.64mA 4V 0.006uA 4V 5.33uA 4V 1.78mA 4V 59.86mA 4.5V 0.005uA 4.5V 5.33uA 4.5V 1.79mA 4.5V 61.28mA 5V 0.006uA 5V 5.33uA 5V 1.80mA 5V 63.87mA 3.4 Build the circuit shown in Fig. 3 in NI Multisim. Use the same MOSFET as that in step 3.2. 3.4.1 Simulate the I-V characteristics ?? v. s. ??? in NI Multisim under the same setting as that in step 3.3. Compare and discuss the results with the measured characteristics in step 3.3. 3.5 A common source amplifier based on ZVN2110A MOSFET is shown in