Revised: Summer 2010

Transcription

1 EE 2274 PRE-LAB EXPERIMENT 5 DIODE OR GATE & CLIPPING CIRCUIT COMPLETE PRIOR TO COMING TO LAB Part I: 1. Design a diode, Figure 1 OR gate in which the maximum input current,, Iin is less than 5mA. Show all work. a. Use two 1N4002 () diodes. b. Verify your design using Pspice. c. Plot the voltage transfer function by varying the input voltage on Pin A while holding the voltage at Pin B to 0V. Assume the A is = to 5V and.7 voltage drop across D1. d. Verify that the maximum current is within specification. FIGURE 1 2. Simulate the circuit again after substituting two D1N914 diodes for the diodes. a. Plot the voltage transfer function by varying the input voltage on Pin A while holding the voltage at Pin B to 0V. b. Determine the maximum input current. Page 1 of 7

2 3. Determine the differences between the diodes. a. Click on in the PSpice simulation, causing the part to be highlighted. b. Select EDIT/MODEL c. In the pop-up window that opens, select EDIT INSTANCE MODEL (Text). d. Scroll through the parameter listed to find RS, the series resistance of the diode, IS, the reverse saturation current, and VJ, the turn-on voltage (or Von) of the diode. e. Repeat these steps with D1N914 to determine RS, IS, and VJ for this diode. Part I: Answers 1. Assume a voltage drop of 0.7V across a diode. Maximum current allowed through resistor is less than 5 ma. Solve for value of R1. R1= from PSPICE= Is maximum current less than 5mA? 2. from PSPICE= 3. For = = = For D1N914 = = = Part II : CLIPPING CIRCUIT Given the circuit in Figure 2 below, sketch the input v i and output v o signals expected if 1. v i = 8 V pp, 1 khz sine + 2 V DC. v o = when -0.7V < v i < 0.7V 2. Repeat part 1 with v i = 8 V pp, 1 khz sine 2 V DC. v o = when -0.7V <vi < 0.7V Page 2 of 7

3 Given the circuit in Figure 3 below, sketch the input v i and output v o signals expected if 3. v i = 8 V pp, 1 khz sine + 2 V DC v o = when -0.7V < v i < 0.7V 4. Repeat part 3 with v i = 8 V pp, 1 khz sine 2 V DC. v o = when -0.7V < v i < 0.7V Verify your sketch with PSpice. Turn in with Pre-Lab Vi R1 1k Vo D1 FIGURE 2 Vi R1 1k Vo D1 FIGURE 3 Page 3 of 7

4 6. Design a clipping circuit as shown below, Figure 4, so that the waveform will be clipped at +3V and 6V. Show all work. Verify your design using PSpice. R1 VOFF = 0 VAMPL = 10 FREQ = 1k Vi 1k V2 D2 V3 Vo D1 FIGURE 4 1. Print out the waveform. Why might the circuit not clip at exactly -6V and +3V? Required Graphs 1. Voltage transfer function of diode or circuit 2. Voltage transfer function of diode or circuit with 1N Transient of Part II.1 4. Transient of Part II.2 5. Transient of Part II.3 6. Transient of Part II.4 7. Transient of -6V and 3V clipping circuit Page 4 of 7

5 LAB EXERCISE EXPERIMENT #5 DIODE GATE AND CLIPPING CIRCUIT Part I. Diode OR GATE: 1. Build an OR gate using 1N4001 same as 1N4002 () except for peak reverse voltage). a. Use the lab workbench software and the DC sweep to plot the voltage transfer function. Sweep from 0-5V in 100mv increments. (Label your graph to be turned in). b. Same as above except plot the output current. Compare the maximum value for the output current with that obtained from your simulation. c. Using the curve tracer to produce the forward-biased characteristic of your 1N4001. Determine V D From the graph and the current in your circuit. Then use the digital multimeter to measure V D. Compare your results. Turn in your graph. Part II. Clipping Circuits: 1. Build the clipping circuit Figure 2 of the pre-lab with an input offset of 2V. Capture the input (vi) and output (vo) waveforms from the oscilloscope. 2. Change the offset of the vi to -2v. 3. Change the direction of the diode Figure 3 change the offset to 2V. 4. Change the offset to -2V and repeat. 5. Build your design for the clipping circuit in Figure 4. Place a probe in order to view V o, the waveform produced. Capture the waveform and print out the waveform to be turned in. a. Does the circuit clip at exactly 6V and +3V? Does it clip at the same values from your PSpice simulation? If not, why would there be differences between the PSpice simulation results and the real life results? b. Now that you know the voltage drop across the diodes you are using in lab, design your circuit so that the source is a 20V pp square wave that after clipping is approximately a 0 to 5V square wave. Build your circuit, capture the waveform and save it to disk to print later. Draw your design schematic on your answer sheet. Page 5 of 7

6 DATA SHEET EXPERIMENT 5 DIODE GATE & CLIPPING CIRCUIT PART I. : a. Print out DC sweep and turn in with data sheet. b. Maximum current in circuit Maximum current in PSPICE % Error c. Print out forward-bias characteristics curve for the 1N4001 diode. The x-axis should be scaled according to the typical voltage drop across a diode. The y-axis should be scaled according to the current that will be flowing through the diode in the circuit. V D (graph) = V D (measured) = Any difference? Why? PART II. Clipping Circuits 1-4. Compare the differences in circuit behavior between having a forward and reverse-biased diode, include scope capture of input (vi) and output ( vo) to turn in with lab. Page 6 of 7

7 5. Turn in waveform. a. Does the circuit clip at exactly 6V and +3V? Why would there be differences between the PSpice simulation results and the real life results? Schematic Drawing: b.turn in waveform. Required Graphs 1. DC Sweep of OR gate, voltage 2. DC Sweep of OR gate, current 3. I-V Characteristic of diode 4. Scope capture of Part II.1 5. Scope capture of Part II.2 6. Scope capture of Part II.4 7. Scope capture of Part II.5 8. Scope capture of Part II.6 9. Scope capture of Part II.6b Page 7 of 7