* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download mi FIG`. 2C
Electrical ballast wikipedia , lookup
Dynamic range compression wikipedia , lookup
Control system wikipedia , lookup
Linear time-invariant theory wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Current source wikipedia , lookup
Signal-flow graph wikipedia , lookup
Negative feedback wikipedia , lookup
Ground (electricity) wikipedia , lookup
Buck converter wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Integrating ADC wikipedia , lookup
Semiconductor device wikipedia , lookup
Oscilloscope history wikipedia , lookup
Analog-to-digital converter wikipedia , lookup
Regenerative circuit wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Two-port network wikipedia , lookup
History of the transistor wikipedia , lookup
Network analysis (electrical circuits) wikipedia , lookup
Schmitt trigger wikipedia , lookup
April 28; 19.70 ‘ v ' w. G. cRous’E‘ ET AL ' 3,509,369. ABSOLUTE VALUE_FUNCTIION GENERATOR Filed July 12. ‘1967 > - 2 Sheets-Sheet 1 E out Rf . Egg ‘ R‘ ' 'ViRl ' ‘AMP °Eoui R1 1 FIG. 16 R2 FIG. Id Rf R “Ry i Eout Ein R1 _ mi 1 ‘ FIG‘. 2C #vvnvroes WILLIAM G. CROUSE WALTER S. DUSPIVA ' ATTORNEY April 28, 71970 w; G‘. 'cRouSE ‘ET AL . 3,509,369 vABSOLUTE‘ VALUE FUNCTION GENERATOR Filed July 12, 19s? ‘ ’ ‘ ’ Rf 'vvZv RX- ' Ry‘ M , M i .k THRESHOLD___ 5"‘ cmcun 2 / _ Q AMP 1 > 2 sheets-$5981 2 - 4E out » ‘0 a: 'Ri R2 ' ‘ FIG. 20 +25v 31 32 - ‘Rx 1;. 19 20 Em<*\3_— _ ' j ‘ W A/MP}l - ?°Eout United States Patent 0 11 3,509,369 CC Patented Apr. 28, 1970 1 2 3,509,369 ing more particular description of preferred embodiments of the invention, as illustrated in the accompanying draw ABSOLUTE VALUE FUNCTION GENERATOR William G. Crouse, Raleigh, N.C., and Walter S. Duspiva, Eurlicott, N.Y., assignors to International Business Ma chines Corporation, Armonk, N.Y., a corporation of lngs. New York Filed July 12, 1967, Ser. No. 652,796 Int. Cl. G07g 7/12; H03k 5/153 U.S. Cl. 307—230 7 Claims 10 ABSTRACT OF THE DISCLOSURE An electronic switch responds to the polarity of input signals to an operational ampli?er of the differential ampli?er type and connects the signals to one or both of the differential ampli?er input terminals. The ampli?er gain is alternatively plus or minus one to provide a low cost absolute value function generator accurate at low voltage levels in the order of plus and minus ?ve-tenths volt. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la-ld inclusive illustrate various operational ampli?er characteristics to aid in a better understanding of the improved function generator; FIG. 2a illustrates the improved function generator partially in schematic form and partially in diagram matic form; FIGS. 2b and 2c illustrate the manner in which the embodiment of FIG. 2a operates in either of its two states; and FIG. 3 is a schematic diagram illustrating one preferred form of the improved function generator. DESCRIPTION OF THE PREFERRED EMBODIMENTS In the analog circuit ?eld, it is often desirable to gen erate an output voltage which is the absolute value of BACKGROUND OF THE INVENTION The invention pertains to the ?eld of analog circuits, some positive or negative input voltage. Mathematically, this may be written as: and speci?cally to a circuit which reproduces at its out 25 and put signals of the same amplitude as the input signals but of one polarity irrespective of the polarity of the input Eout:+Eln for osElnsEmax Eout=_Ein for _Emax$E1ns0 The drawings illustrate an improved absolute value gen erator con?guration, and the evolution of the con?gura value function generators. Known circuits of this type usually utilize a pair of operational ampli?ers and diode 30 tion. The basic circuits around which the improved circuit current steering circuits. Known circuits are characterized is built are a differential input operational ampli?er 1 by relatively high cost, low performance at low voltage and a voltage threshold-switch device 2 (FIG. 3). The levels and relatively poor response to rapid changes in device 2 switches impedance levels for the differential the input signal level. Examples of typical prior art cir signal. Such circuits are frequently referred to as absolute cuits are as follows: (1) Analog Methods by Karplus and Soroka, published in 1959 by McGraw-Hill, speci?cally pp. 75 and 76; and (2) Computer Handbook by Huskey and Korn, pub lished in 1962 by McGraw-Hill, speci?cally pp. 3-73. It is an object of the present invention to provide a 40 ampli?er as the polarity of the input voltage changes, thus setting the gain of the entire system to plus one for positive inputs and minus one for negative inputs. Before the circuit of FIG. 3 is explained in detail, a brief review of two common feedback circuits is of value. FIG. 1a shows the most commonly used scheme for lower cost, improved performance absolute value func incorporating a differential input operational ampli?er tion generator. as a feedback device. The gain of this circuit is approxi mately equal to the negative ratio of the feedback resistor to the input resistor, i.e. SUMMARY OF THE INVENTION An improved absolute value function generator is pro 45 vided by electronically switching the input signal to one or both of a pair of input terminals to an operational ampli?er of the differential ampli?er type, depending A less common con?guration is shown in FIG. 1b. In upon the polarity of the input signal. When the signal is this embodiment, the polarity of the gain is positive, i.e. applied to one of the inuts, the gain of the operational 50 ampli?er is plus one. When the input signal is applied to both inputs, the gain of the operational ampli?er is minus It would seem possible then that some combination one. By providing only one operational ampli?er, the of both con?gurations, together with a threshold switch overall cost of the circuit in relation to accuracy is con siderably reduced. 55 ing device, might result in a circuit that has a gain of either plus or minus one, depending upon the polarity of The input switch includes a differential ampli?er to the input signal. sense input signal polarity with additional amplifying I If the con?gurations of FIGS. 1a and 1b are combined stages for high gain. The last stage performs the switch as illustrated in FIG. 10, the resultant circuit is one that ing function. This permits accurate operation at voltage includes two inputs. The equation for the output voltage levels much lower than a volt. The differential portion of the switch includes a pair of transistors preferably hav ing matched base-emitter voltage-current characteristics for good temperature stability. In addition, the impedance presented by the ?nal ampli?er stage is very low com in FIG. 10 is as follows: Rf Rf To make Eout?Einl the circuit_'Fi)+Einz even more specialized, allow the pared to that provided by oppositely poled diodes of prior 65 second input, Elm, to be proportional to the ?rst input, art devices. This provides signi?cantly better accuracy Em, as shown in FIG. 1d, giving rise to the circuit equation: The improved generator exhibits better performance in an environment of rapid changes in the input signal level. 70 The foregoing and other objects, features and advan It can be seen from an analysis of the equation, that tages of the invention will be apparent from the follow the gain of the circuit in FIG. 1d may be either positive at extremely low voltages close to zero volts. 3,509,369 3 or negative, depending upon the value of the four resistors external to the operational ampli?er, i.e. R1, R2, Ri and Rf. If these resistance values were to be switched properly by a zero input threshold device, the gain of the system could be set to either plus or minus one, thus effecting the desired absolute value function. One method of properly controlling the impedances is to break the input resistor Ri into two series input 4 The junction between the resistors Rx and Ry is con nected to ground potential by way of a common emitter transistor ampli?er 10‘ and a low-valued resistor 11. The emitter electrode of the ampli?er 10 is connected to a neg ative supply terminal 12 by way of a resistor 13 and an adjustable potentiometer 14. The voltage divider comprising resistors 11 and 13 and potentiometer 14 ?xes the emitter potential of transistor 10 at a low neagtive voltage equal in value to the Vce resistors Rx and Ry, as shown in FIG. 2a. The threshold device controls a switch to connect the junction of the 10 drop across the transistor 10 when it is operated at satu resistors Rx and Ry to ground potential. The switch is ration. This will set the collector voltage of the transistor closed for input voltages which are zero or positive and 10 at ground potential when it is saturated. is open for input voltages which are negative. Then, The input. terminal 3 is connected to one input of a differential ampli?er switch 15 comprising a pair of tran sistors 16 and 17. More speci?cally, the input terminal 3 is connected to the base electrode of the transistor ampli ?er 16 by way of a resistor 18. The base electrode of the depending upon the position of the switch, the ampli?er will be utilized in one of the two con?gurations of FIG. 2b or FIG. 2c. FIG. 2b’ illustrates the ampli?er connec tions of the embodiment of FIG. 2a when the switch is closed incident to detection of a positive polarity at the transistor ampli?er 16 is clamped to ground potential by way of oppositely poled diodes 19 and 20*. The function input. FIG. 20 shows the ampli?er connections when the switch is open due to a negative potential at the input. 20 of these diodes is to limit the amplitude of signals applied to the base electrode of the transistor by way of re The component values which will achieve the desired sistor 18. results in FIG. 2a can be determined by use of the for The base electrode of the transistor ampli?er 17 is mulas set forth below. It will be recalled that a gain of connected to ground potential by way of a resistor 21 and plus one is desired for the con?guration of FIG. 2b’ and a gain of minus one for FIG. 2c. Arbitrarily assign the 25 to the wiper of a potentiometer 22 by way of a resistor 23. The potentiometer 22 is connected to positive and following values: negative supply terminals 24 and 25 and the wiper is Ohms adjusted so that it is close to ground potential. R1 ___________________________________ __ 10,000 The emitters of the transistors 16 and 17 are connected R2 ___________________________________ __ 1,000 Rf ____________________________________ __ 100,000 The values of Rx and Ry must now be determined, utiliz ing the following equations: / 30 to a negative supply terminal 26 by way of a common resistor 27. A resistor 28 connects the collector electrode of the transistor 16 to the collector electrode of the tran sistor 17. The collector electrode of the transistor 17 is connected to ground potential by way of a resistor 30 FOR POSITIVE INPUTS 35 and to a positive supply terminal 31 by way of a re sistor 32. The collector electrode of the transistor 16 is con nected directly to the base electrode of a common emitter transistor ampli?er 35. The collector electrode of the ampli?er 35 is connected to a positive supply terminal 36 by way of a resistor 37. The collector electrode of the ampli?er 35 is also connected to the base electrode of the transistor 10 by way of a resistor 38. The base elec trode of the transistor 10 is connected to a negative sup (2) 45 ply terminal 39 by way of a bias resistor 40. The potentiometer 22 is set so that the transistors 16 By substituting the values of R1, R2 and R)‘ in Equation and 17 conduct equally when the input signal Em is at 1 above, we compute the value of Ry to be ten thousand ground potential. The gain of the system will therefore ohms. Substituting the values of R1, R2, R7‘ and Ry into be unde?ned when the input is at ground potential; how Equation 2 above, we ?nd the value of Ex to equal 50 ever, no problem arises since Em equals zero and the out put Eon, will therefore equal zero. When Em goes slightly seventy-three thousand, three hundred ohms. positive, the transistor 16 becomes saturated and the tran It will be appreciated that this is not the only set of sistor 17 turns 011‘. When Em goes slightly negative, the component values which will produce the desired results. transistor 17 saturates and transistor 16 turns off. However, it has been found that these particular values When the transistor ampli?er 35 is in its off state, the give results which are quite good when practical factors 55 positive potential from the supply terminal 36 will bias (such as the linearity of the transistors used in the the transistor switch 10 on to saturation, thereby substan threshold circuit, etc.) are taken into consideration. tially connecting ground potential to the junction between In a practical circuit, the switch illustrated in FIG. 2a the resistors Rx and Ry. This occurs only when the tran is replaced by some type of transistor switching arrange ment which detects the polarity and level of the input sig 60 sistor 16 is in its highly conductive condition as a result of the input signal Em being at a positive potential with nal and clamps the junction of Rx and Ry to ground potential when the polarity of the input signal is positive. The transistor switching circuit 2 of FIG. 3 serves this purpose very well. . The preferred embodiment of FIG. 3 will now be described in detail. In FIG. 3, the ampli?er 1 has one respect to ground. When the input signal Em is at some negative poten tial, the transistor 16 is in its low conductivity state, whereby the transistor 35 is turned on to apply ground potential to the base circuit of the transistor switch 10. With the transistor 35- in its conductive state, the swich 10 is turned off, presenting an open circuit to the junction R2. The same input is connected to the input terminal 3 between the resistors Rx and Ry. by way of the resistor R1. The other input of the ampli The use of extremly well-matched transistors 16 and 17 ?er 1 is connected to the terminal 3 by way of the resistors 70 will obviate the need for the adjustment potentiometer 22. Ry and Rx. The resistor Rx is shown in the form of a The use of a transistor 10 having an unusually low fixed resistor and an adjustable potentiometer for accurate impedance at saturation will obviate the need for the sizing. The feedback resistor R)‘ is also in the form of a adjustment potentiometer 14 and resistors 13 and 11. ?xed resistor and an adjustable potentiometer for accurate dimensioning. 75 In addition, a ?xed value resistor can be used for Rx. input connected to ground potential by way of the resistor 3,509,369 These resistors and potentiometers permit the use of a lower performance, low-cost transistor switch without the gain of the ampli?er to plus one when the input‘ signals are of a selected polarity. 2. An absolute value function generator comprising an operational ampli?er of the differential ampli?er type having a pair of input terminals and an output adversely alfecting accuracy. Chart 1 below sets forth the test results with respect to two circuits constructed in accordance with the details of FIG. 3, utilizing the following component values. The terminal, circuits for which the test results are set forth in Chart 1, utilized the same resistive components and operational ampli?er, but different transistors were utilized to verify input resistor means adapted to receive bipolar input signals and feedback resistor means normally bias ing the ampli?er for operation with a gain of minus satisfactory operation of the circuit independent of the one, transistors utilized. The component values for one suit able implementation of the embodiment of FIG. 3 are as control means modifying the input resistor means to follows: the input signals are of a selected polarity, a source of ground potential and a single input signal change the gain of the ampli?er to plus one when Ohms R1 ___ R2 ___ _ Rx __.. Ry _____ Rf ..___ __._ terminal, 9,988 ..__.._ 9,971 said feedback resistor means connected between the 72,380 ampli?er output terminal and one of the ampli?er input terminals, and 9,939 ___ 99,590 11 13 3.3 20 10,000 14 and ____ 11,660 18 . 2,400 21 22 23 28 1,100 50,000 25 5,100 24,000 30 560 32 _ ____ 30 CHART N0. 1 Input (volts) Circuit N o. 2 output (volts) (volts) . 010 . 100 . 010 . 100 1. 000 3. 000 5. 000 8. 001 10. 002 1. 000 3. 000 4. 998 7. 998 9. 997 . 019 . 108 . 019 . 108 l. 008 3. 006 5. 003 8. 000 9. 998 1. 008 3. 007 5. 006 8. 004 10. 001 third and fourth series resistors connecting the signal input terminal to ground potential, the junction between the third and fourth resistors being connected to the other ampli?er input terminal. 3. The function generator of claim 2 wherein the control means includes 560 Circuit No. 1 output said input resistor means including ?rst and second series resistors connecting the signal input terminal to said one ampli?er input terminal, a switch for selectively connecting the junction between the ?rst and second resistors to ground potential to change the gain of the ampli?er from minus one to plus one. 4. The function generator of claim 3 wherein the con trol means further includes ?rst transistor ampli?er means connected to the input 35 terminal and responsive to the polarity of the input signals to render the switch alternatively effective or ineffective. 5. The function generator of claim 4 wherein the tran 40 sistor ampli?er means render the switch effective to connect the junction between the ?rst and second resistors to ground potential when the polarity of the input signals is positive. 6. The function generator of claim 5 wherein the While the invention has been particularly shown and 45 switch comprises a common emitter transistor ampli?er having its col described with reference to preferred embodiments there lector electrode coupled to the junction between of, it will be understood by those skilled in the art that the ?rst and second transistors and having its emitter the foregoing and other changes in form and details may electrode coupled to ground potential. be made therein without departing from the spirit and 50 7. The function generator of claim 5 wherein said ?rst scope of the invention. What we claim is: transistor ampli?er means comprises a high gain differen tial ampli?er. 1. An absolute value function generator comprising an operational ampli?er of the differential ampli?er References Cited type having a pair of input terminals and an output UNITED STATES PATENTS terminal, 55 means each serially connected to a respective one 3,281,723 3,292,098 10/1966 12/1966 Mercer ________ __ 307—235 X Bensing ___________ __ 330~—69 input terminal and adapted to receive bipolar input signals and including negative feedback resistor 3,305,729 3,413,492 2/1967 11/1968 Stein ____________ __ 307—235 Schneider ________ __ 307-—235 an input circuit including at least two input resistor means connected to one of the input terminals nor 60 mally biasing the ampli?er for operation with a gain of minus one, electronic switch means responsive to the input signals for modifying the input resistor means to change JOHN S. HEYMAN, Primary Examiner US. Cl. X.R. 307-235, 236; 330—30, 69