FACULTY OF ENGINEERING LAB SHEET

Transcription

1 FACULTY OF ENGINEERING LAB SHEET CIRCUITS AND SIGNALS EEL 2186 TRIMESTER 1 (218/219) -Circuit analysis using ORCAD PSpice *Note: You will be given an assessment sheet during the lab session to be completed based on this experiment. You have to submit the sheet before signing out. No lab report is required for this experiment.

2 Experiment : Circuit analysis using ORCAD Pspice PRECAUTIONARY STEPS: 1. Read this experiment sheet thoroughly and carefully before coming to your lab session. 2. Take precautions for safety. Also handle equipment carefully to prevent any damages. 3. Try to get as much of the analysis done during the lab session. 4. Close all running programs other than the OrCAD-PSpice program. 5. Seek the approval of your results for each part of the experiment from your lab supervisor before moving to the next one. 6. Appendix A on page 5 provides some guidelines and examples on how to solve Part You will be given an assessment sheet during the lab session to be completed based on this experiment. You have to submit the sheet before signing out. No lab report is required for this experiment. 1. Objectives: (i) (ii) (iii) (iv) (v) To understand the concept of electronic circuit simulation using a software like OrCAD-Pspice To design passive and active low pass circuits for various orders. To apply the simulation conditions for passive and active low pass circuits for AC sweep analysis. To analyse the simulation results for passive and active low pass circuits. To evaluate the performances of active Butterworth and Chebyshev low pass circuits from the simulation results 2. Introduction: Methods of circuit analysis vary widely depending on the complexity of the problem. Whereas some circuits require nothing more complicated than the writing of a single equation for their solution, others may require several equations to be solved simultaneously. When the response of a circuit is to be performed over a wide range of frequencies, the work is often both tedious and time consuming. In many cases, the problem to be solved requires that the students have an understanding of which basic laws and principles are involved in the solution. In some cases, if the topology of a network is known, along with complete descriptions of the circuit elements, computer programs can be used to perform the analysis. Such programs have been under development for several decades. Dr.Spice and OrCAD- PSpice are among the powerful programs that are capable of solving many types of electrical networks under a variety of conditions. 3. Procedure: Start OrCAD-Pspice A/D Click start Programs Cadence OrCAD Capture CIS lite Part I: Variable Component Sweep Analysis Step 1: From the menu bar click: File New project Step 2: Put name as Project I select Pspice Analog or Mixed A/D OK. (For the circuit as in Figure 1). Select Create a blank project. 2/7

3 out PARAMETERS: Resistance = 2 R1 Resistance L1 1mH IC = -9mA C1 2u, IC = 1v Step 3: Add built-in libraries. To do so, click Place Part on the right-hand side menu. Then under Libraries, click Add Library tab to add the following: Analog ; Source ; Special ; Sourcstm & Eval. Step 4: Draw the circuit as shown in Figure 1: Components needed are as follows: Analog (R-var, L, C) Special (PARAM) Ground (/CAPSYM). {from the vertical menu} Output (Offpageleft-R). {from the top toolbar, under Place, click on Off- Page Connector } Step 5: Key in values: Key in Resistance as value for R1 Capacitor 2u double click capacitor (A new window will pop-up) key in 1 V into IC block (1 V as initial condition) highlight IC click display click Display name and value go back to schematic page Inductor 1 mh double click inductor (A new window will pop-up) key in 9 ma into IC block (-9 ma as initial condition) highlight IC click display click Display name and value go back to schematic page Change the text Offpageleft-R to Out Step 6: Key in reference Double click PARAMETERS (A new window will pop-up) Click New property name Resistance key in 2 as the value Highlight resistance block click display click Display name and value go back to schematic page Step 7: Simulation Click Pspice from menu new simulation profile give any name click create choose Time domain Run to time 2 ms click the box parametric sweep choose global parameter parameter name Resistance start value 2 End value 1 increment 2 click OK Click the small green triangular icon to run the simulation Click add trace Icon click Vout Step 8: Results A simulation result shows the transient response with difference value of resistance R Step 9: OPTIONS Click FFT icon to see the frequency domain picture Figure 1 3/7

4 Part II: Design of Passive Low Pass Filter Step 1: Open a new project named project 2 for the circuit Figure 2. R1 1Ω L1 1mH Out V1 1Vac C1 1u Figure 2 Step 2: Instruct OrCAD to perform AC Sweep analysis with a frequency sweep variable that is to be varied from 1Hz to 1kHz at 1 points per decade in a logarithmic sweep. Step 3: Run simulation. Step 4: Click trace click Vout. Step 5: A result of low pass is displayed. Part III: Design of 1 st Order Butterworth Low Pass Filter Step 1: Open a new project named project 3 for the circuit in Figure 3. VCC+ R1 1Vac V V+ + µa741-4 V VCC+ out 15Vdc V2 15Vdc VCC- V3 C1.1u VCC- Figure 3 Step 2: Instruct OrCAD to perform AC Sweep analysis with a frequency sweep variable that is to be varied from 5Hz to 5kHz at 1 points per decade in a logarithmic sweep. Step 3: Run simulation. Step 4: Click trace click Vout. Step 5: A result of low pass is displayed. *µa741 can be selected from the Eval library. 4/7

5 Part IV: Higher-order low pass Order Butterworth dB Chebyshev Table 1: Higher order low pass parameters. 1 st stage 2 nd stage 3 rd stage R B /R A f R B /R A f R B /R A f Note: Normalized cut-off frequency, f = 1/[2πRC desired cut-off frequency] Overall passband gain (db) Design 3rd and 5 th order Butterworth and Chebyshev low pass s using Table 1. The cutoff frequency for each is as specified in design examples section in Appendix A. Fill up Table-2 (in the assessment sheet) with the calculated resistance values for each designed. R A has been set to 1 Ω for all the s. 5/7

6 Guidelines for Part 4.: Appendix A Higher-order s may be constructed by cascading a combination of 1st and 2nd order sections (stages). The basic structure of 1 st order and 2 nd order low pass sections is shown in Figure A1: R A R B V i V o V i V o Figure A1a: 1 st order low pass network. Figure A1b: 2 nd order low pass network The block diagrams in Figure A2 illustrate the schemes for a higher-order low pass. Odd-order s are obtained by cascading a 1 st order section with one or more 2 nd order sections. For example, a 5 th order low pass can be built by cascading a 1 st order section with two 2 nd order sections. 1 st order 2 nd order 3 rd Order Filter 5 th Order Filter Figure A2: Block diagram illustrating the higher-order low pass s The values and parameters in Table 1 can be used to design the required s in your assignment. Apply the following relationship: f = 1 2πRC where, f c, is the given cut-off frequency. Design examples: 1 st order 2 nd order 2 nd order 1) Third order Butterworth : To design a third order Butterworth low pass with a cut-off frequency of 19.4 khz. Set C =.1µF for all the calculations. f c 6/7

7 By referring to Table 1, it is simple to determine that the selected resistance value should be 82Ω for all 1 st and 2 nd stages of s. = 1 R = Ω 2π.1µ 19.4k 82 2) Fifth order Butterworth : To design a fifth order Butterworth low pass with a cut-off frequency of 19.4 khz. Set C =.1µF in all the calculations. By referring to Table 1, you can determine the suitable resistance values. 3) Third order Chebyshev To design a third order Chebyshev low pass with a cut-off frequency of 21.4 khz. Set C =.1µF in all the calculations. The first stage of the resistance value is calculated as follows: = 1 R = 231Ω Ω 2π.1µ 21.4k By referring to Table 1, you can determine the suitable resistance values. 4) Fifth order Chebyshev To design a fifth order Chebyshev low pass with a cut-off frequency of 2.1 khz. Set C =.1µF in all the calculations. The first stage of the resistance value is calculated as follows: = 1 R = 3551Ω Ω 2π.1µ 2.1k By referring to Table 1, you can determine the suitable resistance values and tabulate in Table 2. Table 2: Tabulation of resistance values for design of low- pass s Name of 1 st stage 2 nd stage 3 rd stage Third-order Butterworth Fifth-order Butterworth Third-order Chebyshev Fifth-order Chebyshev R (Ω) R (Ω) R A (Ω) R B (Ω) R (Ω) R A (Ω) R B (Ω) /7