B EE 331 Lab 1 – Diode Characterization - Su23

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B EE 331 Devices and Circuits I Lab 1 – Diode Characterization Rev. 2023 1/15 Lab 1 – Diode Characterization Introduction The objectives for the lab are: • Learn various methods for characterizing diodes. • Understand and observe the nonlinear 𝑪?𝒓𝒓𝒆?? - 𝑽?𝒍?𝒂𝒈𝒆 ( 𝑰 - 𝑽 ) characteristics of various types of diodes. • Explore the “Forward Bias” characteristics of standard semiconductor diodes • Explore the “Reverse Bias” characteristics of Zener diodes . • Learn to use LTSPICE in simulating individual diode characteristics. • Learn how to plot I-V curve Lab 1 has three components. Assess Method Experiment Topic Time allotted Grading point Team Lab 1 - 0 LT Spice Simulation of diode I-V characteristics 2 hours 20 Team Lab 1 - 1 Measuring diode forward I- V Characteristic 1 hour 40 Team Lab 1 - 2 Measuring Zener Diode I-V Characteristics 1 hour 40 Suggestions: • Prioritize Lab 1-1 and Lab 1-2 for in-person lab sessions • Conduct Lab 1-0 in-person or at home

B EE 331 Devices and Circuits I Lab 1 – Diode Characterization Rev. 2023 2/15 Lab 1-0: LTSpice Simulation of Diode Characterization Reading Assignment Until now we have studied linear circuit components such as resistors, capacitors, and inductors. Linear components have a linear current-versus-voltage relationship. If you double the voltage across the component, the current doubles. Now we will look at our first nonlinear component, the diode. The diode is a two terminal device consisting of an anode (arrow) and a cathode (bar) such as the circuit schematic representation, and picture of an 1N4148 diode shows in Figure 1. In the picture, a black ring is used to mark the cathode (bar) of the diode. The polarity of a diode can be tested with a digital multimeter (DMM) in its diode setting. Touch each probe of the DMM voltage terminals across the diode and note the reading. If the display indicates a positive value (i.e. +0.7 V), then the positive probe is touching the anode, and negative probe is touching the cathode. Figure 1 − The diode schematic symbol with polarity and a 1N4148 silicon diode. A textbook diode has a nonlinear current-versus-voltage relationship (also called an 𝑰-𝑽 curve) such as the one shown below in Figure 2. The diode has two major regions of operation known as the forward and reverse bias regions. In the forward-bias region a positive voltage is applied to the anode (arrow) side of diode. When the voltage exceeds a threshold ( V TH ~ 0.7 V in Figure 2), current conducts through the diode in the direction of the arrow. In the reverse-bias region, a negative voltage is applied across the anode to cathode. In the reverse-bias region, the diode conducts no current (or very little leakage current) until a breakdown voltage is reached. Figure 2 − Diode I-V characteristics.

B EE 331 Devices and Circuits I Lab 1 – Diode Characterization Rev. 2023 3/15 • In Lab 1-1 we will measure the Forward I-V characteristic curve of several typical semiconductor diodes ( 1N4148 silicon diode and the small signal 1N5711 Schottky diodes) that are used for rectification and small signal modulation/demodulation/mixing circuits respectively. • In Lab 1-2 we will measure the Forward/reverse I-V characteristic curve of Zener diodes 1N4732 and 1N4744 . LTSpice Simulations of Diode Circuits Introduction SPICE simulations can be used to plot I-V characteristics of individual diodes. In these prelab we prefer to use the LTS pice simulator available for MAC’s or PC’s as a free software download at www.analog.com . However, any SPICE simulator of the student’s choice is equally applicable. We will learn how to use a DC Sweep operation in LTSpice to obtain an I-V characteristic curve for an individual diode. Procedure for LTSpice Simulations of Diode 𝑰 - 𝑽 Characteristics (1) Open the LTS pice simulator and “build” the LT Spice circuit shown in Figure 3 with the step-by- step procedure given below. Figure 3 – LTSpice Diode Curve Tracer Schematic (2) In the toolbar at the top of the screen select the diode symbol. Place it in the schematic. Right click on the diode symbol and a dialog box will appear ( Diode – D1 ). Select: Pick New Diode , and the dialog box ( Select Diode ) will appear. Find the 1N4148 diode and select it. (3) Now, as shown in the schematic, connect a voltage source and a 500 Ω resistor to the anode of the diode. Ground the cathode of the diode and the voltage source. Label the voltage at the voltage source, IN and the output voltage diode . Right click on the voltage source and a dialog box ( Voltage Source V1 ) will appear. Set DC value[V] to 0. (4) Run the simulation. Select DC Sweep and a dialog box ( Edit Simulation Command ) will appear as shown below in Figure 4. Enter the quantities shown in Figure 5 and click OK.

B EE 331 Devices and Circuits I Lab 1 – Diode Characterization Rev. 2023 4/15 Figure 4 – Edit Simulation Command (5) A blank plot window will appear after the simulation has run. Add traces by right clicking in the plot window and selecting Add Traces . A dialog box ( Add Traces to Plot ) will appear. Select I(R1) since R1 is the resistor in series with the forward biased diode. A plot of the series current versus the V1 voltage sweep should appear. (6) Now we will show how to format this plot for cutting and pasting into a Lab Report. Points will be subtracted in lab reports where plots are not given with white backgrounds, visible waveform widths, legible axis, gridlines and labels . To change the color of the background to white, select Tools in the plot window toolbar and then select Color Preferences . A dialog box ( Color Palette Editor ) will appear and select; Item Background Selected Item Color Mix: All the colors to 255 (7) To make the traces thicker, select Tools in the plot window toolbar and then select Control Panel . A dialog box ( Control Panel ) will appear and select Waveforms , Data Trace Width = 3. The plot output of I(R1) versus V1 should look like Figure 5.

B EE 331 Devices and Circuits I Lab 1 – Diode Characterization Rev. 2023 5/15 Figure 5 – LTSpice DC Sweep (8) To plot the diode current I(R1) versus the diode voltage V(diode) on the horizontal axis (like an I-V characteristic on an x-y instrument display) move the cursor over the horizontal axis until a ruler appears. Right click and a dialog box ( Plot Limits ) appears. Enter the Quantity Plotted: V(diode) . (9) To set the horizontal and vertical axis, select Plot Settings in the plot window toolbar and then select Manual Limits . A dialog box will appear ( Plot Limits ) and set the limits to the values shown below; Vertical Axis Top: 20mA Tick: 1mA Bottom: 0mA Horizontal Axis Left: 0V Tick: 50mV Right: 750mV The plot should now appear as given in Figure 6 below.

B EE 331 Devices and Circuits I Lab 1 – Diode Characterization Rev. 2023 6/15 Figure 6 – LTSpice Output Diode Current versus Diode Voltage for 1N4148 (10) Now the student can further format and annotate this plot if it is asked for in the Lab Report. One can then copy a screenshot of the output by choosing Copy bitmap to Clipboard under Tools in the toolbar. This bitmap screenshot can then be pasted directly into a Lab Report if asked for. However, in this lab we will export the simulated data and plot our LTSpice simulations along with measured data in the same Excel plot. Therefore, we will discuss how to do this next (11) To export the data into a text file (an ASCII text file that can be read by any text editor or Excel spreadsheet), we can choose Export Data as Text under the File toolbar. When the dialog box ( Select Traces to Export ) appears, hold the control key and select V(diode) and I(R1) before clicking OK . In File , enter the name 1N4148 SPICE.txt. Now it can be opened in Excel and plotted along with the measured data. (12) Repeat this procedure for generating LTspice simulation data for the 1N5711 Schottky diode. 2.2 LTspice Simulations of Zener Diode Circuits (1) Repeat procedure for generating LTSpice simulation data for the 1N4732 Zener diode. Note: These diodes are not supplied with LTSpice, therefore you will have to download a SPICE model from the web and set it up in your LTSpice simulator . Manufacturers typically supply these SPICE models, which include the parameters for the diode. Read and research the LTSpice manual on how to do this. (2) For Zener diode, please simulate for voltages -5 V to 1V so that the I-V curve shows both the reverse breakdown and forward bias.

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