COMPUTER AIDED DESIGN OF OPERATIONAL¢AMPLIFIER CIRCUITS¢¢By David Hayes¢¢¢OPERATIONAL AMPLIFIERS / CAD¢XXX¢ This program can aid you in the¢design of most operational amplifier¢(OP AMP) circuits. Hence its name,¢Computer Aided Design (CAD). Your¢computer can now remove the burden of¢making numerous calculations from your¢design task. Its spreadsheet-like¢operation allows you to instantly see¢the effects of any circuit changes you¢make. If you have an Atari 825¢80-Column Printer (or just about¢standard printer Ws attached, you can¢get a record of your design effort.¢¢XXX¢ Although some knowledge of OP AMP¢circuit design is required, this¢program should find wide use among¢students and hobbyists as well as¢professionals.¢¢ REQUIRED: Atari BASIC language¢and minimum 48K memory. OPTIONAL:¢Printer¢¢XXX¢LOADING CAD INTO COMPUTER MEMORY¢¢ Insert the program disk in drive 1,¢power up the printer if it will be¢used, and then boot the computer with¢Atari BASIC enabled. The program will¢run automaticaly.¢¢MAIN MENU SCREEN¢¢ After the title screen, the program¢will automatically proceed to the¢first menu screen, containing¢functions, commands, and menus.¢XXX¢¢ Your computer can provide some HELP¢at any step along the way. If you¢would like some help just press the¢[H] key during normal program¢operation.¢¢ Press [SELECT] to highlight the¢different circuits listed on the menu.¢Press [START] when the circuit you¢want is highlighted.¢XXX¢¢DESIGN NOTES¢¢ Once you make your selection, a¢design screen will be displayed.¢Design notes and general circuit¢information follow.¢¢ If you are a beginner, you may wish¢to fist review the design example¢described in the section labeled¢SAMPLE APPLICATIONs.¢¢XXX¢ If you have a printer but do not want¢a printout of your designs, just turn¢your printer off.¢¢KEY FUNCTIONS¢¢[RESET] - Return control to the main¢menu.¢¢[SELECT] - Selects component to be¢changed.¢¢[OPTION] - Change circuit¢configuration, if supported.¢¢XXX¢[START] or [RETURN] - Enters a new¢value for the selected component.¢Then the program displays the effect¢of this change.¢¢[H] - Display HELP messages.¢¢[0] through [9] number keys - Used to¢input a new component value.¢¢XXX¢Below are notes on the individual types of circuit:¢¢INVERTER OP AMP¢¢Circuit Characteristics:¢¢1) Gain can be less than, equal to,¢or greater than one.¢¢2) Input impedance is equal to R1.¢¢Calculated Values:¢¢1) R3=R1*R2/(R1+R2)¢2) GAIN=-R2/R1¢XXX¢NON-INVERTING OP AMP¢¢Circuit Characteristics¢¢1) Gain must be greater than one.¢¢2) Input impedance is very large.¢¢Calculated Values¢¢1) GAIN=(R1+R2)/R1¢¢XXX¢SCHMITT TRIGGER/COMPARATOR¢¢Circuit Characteristics¢¢1) Provides rapid output transition.¢It is most often used as a buffer¢between analog and digital circuits.¢¢2) This circuit will act as a¢comparator for values of T less than¢one. When T is greater than one then¢the circuit will act as a true Schmitt¢trigger.¢XXX¢¢3) T is typically made much greater¢than one to account for large¢variations in the open loop gain¢(AOL).¢¢Calculated Values¢¢1) T=R1*(AOL)/(R1+R2)¢¢INTEGRATOR¢¢XXX¢Circuit Characteristics¢¢1) The output is equal to the gain¢times the integral of the input¢voltage.¢¢Calculated Values¢¢1) GAIN=-1/(R1*C1)¢2) R2=R1¢¢XXX¢DIFFERENTIAL (DIFFERENCE) AMPLIFIER¢¢Circuit Characteristics¢¢1) Input impedance to V1 is R1, V2¢R2, and V3 R3.¢¢2) R1 must be equal to R3, and R2¢must be equal to R4 for this circuit¢to be a true differential amplifier¢. Ideally, a differential amplifier¢should not amplify signals which are¢not common to both inputs. However, a¢1% deviation in any one of the¢resistances will cause a large¢¢XXX¢reduction in its ability to reject¢common mode signals.¢¢Calculated Values¢¢1) OUTPUT=((R1+R2)/(R3+R4))*(R4/R1)*¢V2-R2/R1*V1¢¢XXX¢ADDER (SUMMING) AMPLIFIER¢¢Circuit Characteristics¢¢1) Output is the inverted sum of all¢input signals.¢¢Calculated Values¢¢1) OUT=-R4*(V1/R1+V2/R2) NOTE: Two¢input option.¢¢2) OUT=-R4*(V1/R1+V2/R2+V3/R3) NOTE:¢Three input option.¢¢XXX¢3) R5=1/(1/R1+1/R2+1/R4) NOTE: Two¢input option.¢¢4) R5=1/(1/R1+1/R2+1/R3+1/R4) NOTE:¢Three input option.¢¢SAMPLE APPLICATION¢¢Let's design an inverting op amp¢amplifier circuit...¢¢XXX¢Step 1: [SELECT] the inverter circuit¢from the main menu. When the word¢INVERTER is highlighted, press¢[START]. The CAD program will load¢from the disk and display the selected¢circuit.¢¢XXX¢Step 2: Again, press [SELECT] to see¢which circuit parameters you can¢modify. Pause at some component, then¢enter a value for it. Your new value¢is displayed, and all parameters¢affected by your change will be¢updated. You may wish to consult your¢Design Notes at this point.¢¢XXX¢Step 3: Repeat Step 2 as often as¢necessary to get the right values.¢Experiment freely. If you make a¢mistake the computer will recover and¢display an error message. It's just¢that simple.¢¢êRemember, press [H] for Help. **¢¢XXX¢ADVANCED TECHNICAL INFORMATION¢¢The integrated circuit OP AMP is the¢workhorse of linear amplifiers used in¢most audio equipment. Its low cost¢and high performance has made it the¢amplifier of choice among¢professionals, students, and hobbyists¢alike. The generic 741 and improved¢versions are typical of this group.¢XXX¢Most OP AMPs of 741 quality or better¢can be readily used to construct the¢circuits designed with this CAD¢program. I suggest that you consult¢any of the many good texts and¢application notes for details of¢circuit design and OP AMP selection.¢Your local electronics shop probably¢stocks many of these books.¢¢XXX¢You may wish to pick up the¢"Engineer's Mini-Notebook, Op Amp IC¢Circuits" by Forrest M. Mims III.¢This book is available from Radio¢Shack, catalog number 276-5011. It is¢filled with many excellent examples of¢the 741 and several popular OP AMPS.¢(Radio Shack also sells the 741 OP¢ AMP.)¢¢XXX¢Resistors and capacitors come in¢industry standard sizes. The program¢will accept standard and non-standard¢values. However, you may have¢difficulty building your circuit with¢non-standard component values. So,¢for your reference, the standard¢(common) values are noted below.¢¢XXX¢STANDARD COMPONENT VALUES¢¢RESISTORS¢¢OHMS OHMS OHMS OHMS OHMS OHMS OHMS¢2.2 20 180 1.6K 15K 130K 1.2M¢2.4 22 200 1.8K 16K 150K 1.3M¢2.7 24 220 2.0K 18K 160K 1.5M¢3.0 27 240 2.2K 20K 180K 1.6M¢3.3 30 270 2.4K 22K 200K 1.8M¢3.6 33 300 2.7K 24K 220K 2.0M¢3.9 36 330 3.0K 27K 240K 2.2M¢4.3 39 360 3.3K 30K 270K 2.4M¢4.7 43 390 3.6K 33K 300K 2.7M¢5.1 47 430 3.9K 36K 330K 3.0M¢¢XXX¢5.6 51 470 4.3K 39K 360K 3.3M¢6.2 56 510 4.7K 43K 390K 3.6M¢6.8 62 560 5.1K 47K 430K 3.9M¢7.5 68 620 5.6K 51K 470K 4.3M¢8.2 75 680 6.2K 56K 510K 4.7M¢9.1 82 750 6.8K 62K 560K 5.1M¢10 91 820 7.5K 68K 620K 5.6M¢11 100 910 8.2K 75K 680K 6.2M¢12 110 1.0K 9.1K 82K 750K 6.8M¢13 120 1.1K 10K 91K 820K 7.5M¢15 130 1.2K 11K 100K 910K 8.2M¢16 150 1.3K 12K 110K 1.0M 9.1M¢18 160 1.5K 13K 120K 1.1M 10M¢¢XXX¢CAPACITORS¢¢FARAD FARAD FARAD FARAD¢10pf 100pf 4.7nf 100nf¢22pf 220pf 10nf 220nf¢39pf 330pf 22nf 330nf¢47pf 470pf 33nf 470nf¢68pf 1.0nf 47nf¢
