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.››ˆRemember, 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›