US3482169A

US3482169A - Function simulator

Info

Publication number: US3482169A
Application number: US536124A
Authority: US
Inventors: Neal Duane Peterson
Original assignee: Foxboro Co
Current assignee: Schneider Electric Systems USA Inc
Priority date: 1966-03-21
Filing date: 1966-03-21
Publication date: 1969-12-02
Anticipated expiration: 1986-12-02

Description

Dec. 2, 1969 .N. D. PETERSON 3,482,169

FUNCTION SIMULATOR Filed March 2l, 1966 5 Sheets-Sheet l www www www www www www ww www www w wwwwgwmww wm www www www ww www Ew wwwww um www s w R. N j/ I i/ V, \\*Ym% www1. 2g .n www. www -Hm www www awww@ www .wbw www www www www Mw www ,www vww Ww www www w|ww www www Tw wwww m I l 1| www wlll I :Nw t1. l |wm\w|1|wm| 1w www mmw @Nr www: RANT w.. ww? L w r, ww ww ww\\ ww\ w.w\\vw\ ww v www www ww Q T L# E L v: www ww. ww uw w W wmf i l Il l [L l ||:l I|.l IILVII Illh .fw www d w u Y NMS QQ WQ #www 5 w wm \w\ ww www www www ww w 4E @www ww w. w wwwmw uw |v ni/ww www www www .ww www INIL l Il 7g/af M# ATTORNEYS Dec. 2, 1969 .N. o. PETERSON FUNCTION SIMULATOR 5 Sheets-Sheet 2 Filed March 21. 1966 INVENTOR. NEAL D. PETERSON ATTORNEYS Dec.. 2, 1.969 .N.- D.- PETERs'oN FUNCTION SIMULATOR 5 Sheets-Sheet 3 Filed March 21. 1966 IoUT INVENTOR. NEAL D. PETERSON ATTORNEYS United States Patent O 3,482,169 FUNCTION SIMULATOR Neal Duane Peterson, Brockton, Mass., assignor to The Foxboro Company, Foxboro, Mass. Filed Mar. 21, 1966, Ser. No. 536,124 Int. Cl. H03k 3/04 U.S. Cl. 328-59 17 Claims ABSTRACT F THE DISCLOSURE An electronic converter having a non-linear transfer characteristic which is adjustable to provide a wide variety of transfer functions. The input signal to be translated is coupled simultaneously to a plurality of shaping circuits each having a transfer characteristic represented by a straight line graph. The slopes and starting points of each of the straight line graphs are adjustable and are so set that the composite of the individual graphs is a curve representative of the desired composite transfer characteristic. The outputs of the shaping circuits are combined in a summing differential amplifier provided with negative feedback, and switch means are used to connect the output of each individual shaping circuit selectively to one or the other of the amplifier input terminals, so as to effect an additive or substractive combining of the respective shaping circuit signal. Additional switch means are provided to connect the shaping circuits in the feedback path of the amplifier, to produce certain types of transfer functions not readily obtainable by the direct coupling arrangement.

The present invention relates to apparatus for simulating functions and, more particularly, to electronic circuitry having transfer characteristics adjustable to simulate any selected one of a wide variety of functions. The transfer characteristic of an electronic circuit can be represented as a curve derived by plotting the values of an output current o1' voltage representing the dependent variable along one axis, for example, the ordinate axis, against the values of an input current or voltage representing the independent variable along a second axis, for example, the abscissa.

It is well known that a curve may be approximated by a series of straight-line segments and that the resulting curve approaches the desired curve as the lengths of the straight-line segments are shortened. This technique has formed the basis for the design and construction of`a number of well known function simulators. However, equipment of this nature which is presently available commercially generally suffers from certain shortcomings and limitations. For some of these function simulators, it has been found difficult to precisely adjust the slopes and starting points in the straight-line segments. In others, the adjustments of the slope and starting points of one straight-line segment are not sufficiently independent of some of the other straight-line segments as to make possible simple and rapid adjustments. On the other hand, those equipments which solve these problems, either partially or fully, have been found to be relatively complex in construction and expensive to manufacture.

It is an object of the present invention to provide new and improved apparatus for simulating arbitrary functions.

It is another object of the present invention to provide electronic circuitry having adjustable transfer characteristics.

It is a further object of the present invention to provide apparatus of the character described which overcomes the limitations and shortcomings of presently known comparable equipment.

Basically, the circuitry of the present invention may be considered as a current-to-current converter which has a gain or transfer characteristic dependent upon the level of the input signal current and which delivers an output signal current which is a desired function of the input signal current. In accordance with one embodiment of the present invention, an input signal is coupled simultaneously to a plurality of shaping circuits each having a transfer characteristic represented by a straightline graph. The slopes and starting points of each of the straight-line graphs are adjustable and are so set that the composite of the individual graphs is a curve representative of a desired composite transfer characteristic. Accordingly, the output of the shaping circuits are cornbined by a summing amplifier provided with feedback. In one preferred form of the invention, the slopes of all the straight-line graphs are of the same sign and the proper polarities are assigned to the individual graphs through the use of a differential amplifier as the summing amplifier. For this arrangement, the desired polarities are assigned to the slopes by selectively coupling the outputs of the shaping circuits to either the positive or negative inputs of the differential amplifier, the selection of the input of the differential amplifier to which any shaping circuit is to be connected being dependent upon the desired polarity of the straight-line graph representing the transfer characteristic of that shaping circuit.

A feature of the present invention is that the shaping circuits may be so located as to respond directly to the input signal or they may be located in the feedback path of the summing amplifier. By providing these alternative locations of the shaping circuits, the range of functions which may be simulated is greatly increased.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description, taken in connection `with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings:

FIGURES 1A and 1B are circuit diagrams of one embodiment of the present invention; and

FIGURE 2 illustrates a typical curve which may be simulated by the circuitry of FIGURES 1A and 1B.

The circuits of FIGURES 1A and 1B are interconnected by the conductors having similar reference numerals in both figures. Referring to FIGURES 1A and 1B, the circuitry shown includes a plurality of shaping circuits 10a-10h, each shown within dotted lines, and all of identical construction and operation. Because of the similarity of the shaping circuits, the rdetails of

only circuits

10a and 10b have been shown. Each of the shaping circuits include an emitter-follower comprising a transistor 11a, 11b etc., an adjustable emitter load in the form 'of a

potentiometer

12a, 12b etc., and a

diode

13a, 13b etc., interposed between the transistor and one end of the potentiometer. The second end of each of the

potentiometers

12a, 12b etc., is connected to ground.

-Each of the shaping circuits 10a-10h. also include adjustable biasing means for individually biasing the emitter-followers at predetermined levels. The shaping circuit biasing means include potentiometers 14a, 14b etc., connected between sources of positive and negative potential. The wiper arms 15a, 15b etc., Iof the potentiometers 14a, 14b etc., are connected to the base electrodes of transistors 11a, 11b etc. The magnitude of the Voltage across the potentiometers 14a, 14b etc., and the positions of the wiper arms 15a, 15b etc., determine the bias levels of the respective emitter-followers.

Supply voltage for the emitter-followers is provided along a conductor 20 to which the collector electrodes of transistors 11a, 11b etc., `are connected. As shown in 3 FIGURE 1B, conductor 20 leads from the junction of a Zener diode 22 and a resistor 24 connected between the Zener diode and a source of positive potential. The Zener diode 22 serves to protect the transistors 11a, 11b etc., by limiting the voltage applied to the collector electrodes of the transistors.

The transfer characteristic of each of the shaping circuits a-10h corresponds to the gain of the shaping circuit and can be represented by a straight-line graph having a slope determined by the positions of wiper arms 16a, 16h etc., of

load potentiometers

12a, 12b etc. These potentiometers, therefore, will be referred to as the slope potentiometers.

The starting points of the straight-line graphs correspond to the input signal levels which will render the shaping circuits conductive and are determined by the positions of the wiper arms a, 15b etc., of bias potentiometers 14a, 1417 etc. These potentiometers, therefore, will be referred to as the starting point potentiometers.

A typical composite transfer characteristic is represented by the solid curve illustrated in FIGURE 2. This curve is derived by combining individual straight-line graphs such as the ones shown dotted in FIGURE 2. It will be noted, however, that for the particular circuitry employed in the shaping circuits in FIGURE lA, the output signals on the wiper arms 16a, 16b etc., of the

slope potentiometers

12a, 12b etc., are always positive so that the straight-line graphs which represent the gains and transfer characteristics of the shaping circuits have only positive slopes. In order to develop straight-line graphs having either positive or negative slopes, a differential amplifier 34 is employed as the summing component for combining the individual straightline graphs. The wiper arms 16a, 16h etc., of the

slope potentiometers

12a, 12b etc., are selectively coupled through a plurality of resistors 17a, 17b etc., and a plurality of switches 26a-26h to the positive and negative inputs of the differential amplifier 34. The selection of the input to which any shaping circuit is to be connected is dependent upon the desired sign of the straight-line graph representing the transfer characteristic of that shaping circuit. Where it is desired to have a transfer characteristic represented by a straight line having a positive slope, the respective shaping circuit is coupled to the positive input of the differential amplifier, while for characteristics represented by a straight line having a negative slope the respective shaping circuit is coupled to the negative input of the differential amplifier.

The switches 26a-26h are double-pole, double-throw, center-off switches. The

switch blades

27a and 28a of switch 26a move together between

switch contacts

29a, 30a and 31a, 32a, respectively. The remaining switches 26b-26h function similarly. The switch contacts 2911-2911 and 32a-32h are connected together and to the negative input of the differential amplifier 34. The switch contacts 30a-30h and 31a-31h are connected together and to the positive input of the differential amplifier. The arrangement is such that when one switch blade of any of the switches 26a-26h is connected to one input of the differential amplifier, the other switch blade of the switch is connected to the other input of the differential amplifier. In this way, the wiper arms 16a, 16h etc., of the slope potentiometers may be selectively coupled to either the positive or negative inputs of the differential amplifier 34. Resistors 17a, 17b etc., serve as the high resistance current summing resistors for the differential amplifier 34. The switch blades 28a-28h are connected to ground through resistors 18a, 18h etc. These resistors serve as dummy current summing resistors and ensure that the inputs of the ydifferential amplifier are balanced for any combination of connections between the shaping circuits and the inputs of the differential amplifier 34.

The differential amplifier 34 may be of conventional construction and operation. An input capacitor 35 connected between the positive input to the amplifier and ground and a feedback capacitor 36 serve as balancing filter capacitors. The output of the differential amplifier 34 is connected by means of a conductor 38 to an output amplifier 40 shown in FIGURE 1B. Amplifier 40 having ione or more stages of amplification, only one stage of amplification being shown in FIGURE 1B, serves to amplify the signals from the differential amplifier and to deliver an output signal at terminals 42a and 42b. A resistor 44 connected to the output of the differential amplifier 34 together with a potentiometer 46 connected between ground and a source of positive potential provide a bias voltage for the input stage of amplifier 40'.

The output terminal 42b is connected to ground through a conductor 48, a switch blade 501; of a six-pole, doublethrow switch 50, a conductor 52 and a resistor 54. A feedback signal is developed across resistor 54 which is applied to the negative input of the differential amplifier 34 through a resistor 56, a switch blade 50c of switch and a conductor 58. This feedback signal performs the usual function lof maintaining the potential across the input terminals of the differential amplifier 34 at virtually zero. Resistor 56 serves as a high resistance current summing resistor for this input to the differential amplifier 34.

The composite transfer characteristic represented by the solid curve of FIGURE 2 is derived by -combining the six straight-line graphs a' through f. Graph a has a positive slope, while graphs b through j have negative slopes. Accordingly, the switches 26a-26h at the outputs of the shaping circuits are arranged to connect the output of one of the shaping circuits to the positive input of the differential amplifier 34 and to connect the outputs of five of the shaping circuits to the negative input of the differential amplifier. The switches at the outputs of two of the shaping circuits are placed in center-off positions since their respective shaping circuits are not needed in the development of this composite transfer characteristic.

Shaping circuit 10a is selected for the development of graph a, while shaping circuits 10b 10f are selected for the development of graphs b through j, respectively. Accordingly, the

slope potentiometers

12a, 12b etc., of shaping circuits 10a-10j are set to establish the proper transfer characteristics for these shaping circuits.

The points SPa-SP on the abscissa axis in FIGURE 2 indicate the starting points of the straight-line graphs and correspond to the input signal levels which will render the shaping circuits conductive. Accordingly, the starting point potentiometers 14a, 141; etc., of shaping circuits 10a-10f are set to bias these shaping circuits at cut-off levels corresponding to the points SPa-SP.

An input signal IIN is supplied at a pair of input terminals 60a and 60h, terminal 60h being connected to ground. The input signal is applied to the shaping circuits through a switch blade 50a of switch S0, a conductor 62, a conductor 98 and an amplifier 64. Amplifier 64 is designed to have unity gain and serves as a buffer to prevent loading at the input terminals 60a and 60h by the shaping circuits. Connected between the positive input of amplifier 64 and ground are a pair of

diodes

66 and 68 and a resistor 70. Resistor is a precision scaling resistor which establishes the span of the input voltage to the buffer amplifier 64. The

diodes

66 and 68 are semiconductor devices which provide temperature compensation. As the temperature varies, the resistance of the

diodes

66 and 68 varies accordingly. The changes in resistance of the

diodes

66 and 68 cause corresponding changes in the amplitude of the input signal to the buffer amplifier 64.

The output of the buffer amplifier 64 is connected to ground through a resistor 72. and is also connected through a translating circuit 74, to be considered in more detail hereinafter, to all the starting point potentiometers 14a, 14b etc. If the amplitude of the signal from the buffer amplifier 64 is sufficient to overcome the cut-off bias of any of the shaping circuits 10a-10h, the emitterfollowers in those circuits in which the cut-off bias has been overcome are rendered conductive.

If the amplitude of the input signal to the shaping circuits is greater than SPa, which may or may not be zero, but less than SPb, the emitter-follower in shaping circuit a is rendered conductive. The graph a defines the relationship between the amplitude of the output signal from shaping circuit 10a to the amplitude of the input signal. The slope of graph a is determined by the position of the wiper arm 16a of the slope potentiometer 12a. So long as the amplitude of the input signal to the shaping circuits is less than SPb, the emitter-followers in the remaining shaping circuits remain nonconductive. Under these conditions, the composite transfer characteristic of the shaping circuits corresponds to the individual transfer characteristic of shaping circuit 10a which is represented by graph a.

=If the amplitude of the input signal to the shaping circuits is greater than SP1, but less than SPC, the emitterfollowers in shaping

circuits

10a and 10b are rendered conductive. Graph a again defines the relationship between the amplitude of the output signal from shaping circuit 10a to the amplitude of the input signal. The mirror image of graph b about the abscissa axis defines the relationship between the amplitude of the output signal from shaping circuit 10b to the amplitude of the input signal. The slope of graph b is determined by the position of wiper arm 16b of slope potentiometer 12b. So long as the amplitude of the input signal to the shaping circuits is less than SPC, the emitter-followers in shaping circuits 10c-10h remain non-conductive. By having the switch blade 27b in contact with switch contact 29b, the output of shaping circuit 1Gb is connected to the negative input of the differential amplifier 34. This connection is effective in assigning a negative slope to graph b. Under these conditions, the composite transfer characteristic of the shaping circuits corresponds to the difference between the individual transfer characteristics of shaping

circuits

10a and 10b. This difference is represented by graphs a-b.

In a like manner, the emitter-followers in the remaining shaping circuits 10c-10h become conductive for greater amplitudes of the input signals applied to the shaping circuits. The composite transfer characteristic of the shaping circuits for any particular input signal level is dependent upon which emitter-followers have been rendered conductive, the settings of the wiper arms of the slope potentiometers and to which of the two inputs of the differential amplifier 34 the shaping circuits are connected. The composite curve in FIGURE 2 is seen to be composed of a series of straight-line segments which result from the combination of straight-line graphs a through f. The shorter the straight-line segments, the closer the composite curve approximates the desired curve. A switch blade 94a movable between a pair of switch contacts 94h and 94e is provided to select whether four or eight straight-line segments are to be used in approximating the desired curve. The closer the starting points of the individual straight-line graphs and the more graphs employed, the closer the approximation of the desired curve. With switch blade 94a in contact with switch contact 94b as illustrated, up to eight straight-line segments may be developed. For simpler functions, the last four shaping circuits may be omitted. In this event, switch blade 94a is placed in contact with switch contact 94C, and the source of negative potential previously applied to the starting point potentiometers in shaping circuits 10e-10h is transferred to a resistor 93, connected between switch contact 94c and the sour-ce of positive potential, thus serving to maintain the load across the bias voltage supply constant.

The

diodes

13a, 13b etc., in the shaping circuits serve to prevent reverse current ow. This ensures smooth transitions in the development of one straight-line segment after another.

Also connected to the positive input to the differential amplifier 34 is a translating circuit 80 which serves to shift the composite solid curve in FIGURE 2 vertically. Translating circuit includes a plurality of resistors 82a-82e connected between a plurality of switch contacts 84a-84f. Switch contacts 84a and 84]c are connected to sources of positive and negative potential, respectively. A pair of switch blades 86a and 86h, ganged together, may be moved between pairs of contacts 84a-84f. Connected between switch blades 86a and 8617 is a potentiometer 88 having its wiper arm 88a connected to a resistor 89. The other end of resistor 89 is connected to the positive input to the differential amplifier 34 through a switch blade 50d of switch 50 and

conductors

90 and 92. Resistor 89 serves as a high resistance current summing resistor for this input to the differential amplifier.

The translating circuit 80 provides a D-C signal to the differential amplifier 34 which shifts the level of the output signal accordingly. The effect of this D-C signal is to shift the position of the composite curve of FIGURE 2. The amount of the shift and the direction of the shift is dependent upon the positions of switch blades `86a and 86b and the wiper arm 88a of potentiometer 88.

The translating circuit 74 at the output of buffer amplifier 64 may be of generally similar construction and operation t0 the translating circuit 80. Translating circuit 74, however, serves to shift the composite solid curve of FIGURE 2 horizontally. This is accomplished by adding a D-C signal to the input signal to the shaping circuits with the result that the starting points of graphs a through f are reached for either smaller amplitudes or greater amplitudes of the input signals dependent upon whether the added D-C component is positive or negative.

As previously mentioned, a feature of the present invention is that the shaping circuits 10a-10h may be so located as to respond directly to the input signal or they may be located in the feedback path leading from the output terminal 42b to the input of the differential amplifier 34. This feature greatly increases the range of curves which may be simulated. In general, the shaping circuits are located to respond directly to the input signal for the simulation of curves which can be considered concave. On the other hand, the shaping circuits are located in the feedback path for the simulation of curves which can be considered convex. The six-pole switch 50 serves to locate the shaping circuits. For the positions of the switch blades 50a-501c shown in FIGURE 1A, the shaping circuits are located, as previously described, to respond directly to the input signal. With the switch blades 50a-501 in their alternate positions, the shaping circuits are located in the feedback path leading from output terminal 42b to the input to the differential amplifier 34.

Assuming the switch blades 50a-507c are moved to their alternate positions, the input signal at input terminals 60a and 6017 -is coupled through switch blade 50a and is applied across the resistor 54, previously identified as the feedback resistor. The input signal is conducted through conductor 96, resistor 56, switch blade 50c and conductor 92 to the positive input to differential amplifier 34. The output terminal 42b is connected to the positive input of buffer amplifier 64 through conductor 48, switch contact 50h and

conductors

97 and 98. The output terminal 42b is thus connected to ground through

diodes

66 and 68 and resistor 70, previously identified as the precision scaling resistor. It is seen that

resistors

54 and 70 have switched locations and functions. The output of buffer amplifier 64 is coupled to the inputs of the shaping circuits 10a-10h and the outputs of the shaping circuits are connected to the inputs of the differential amplier 34 through switches 26a-26h.

With switch 50 in its alternate position, another input is supplied to the differential amplifier 34. The junction of diode 68 and resistor 70, at which the output signal from terminal 42b appears, is connected to a resistor 95 which, in turn, is connected through switch blade 50e to the negative input of the differential amplifier. Resistor 95 serves as a high resistance current summing resistor for this input to the differential amplifier. The purpose of this input to the differential amplifier is to develop a ninth straight-line graph of calibrated slope which provides negative feedback at all times when switch S is in its alternate position. In the absence of resistor 95 and with all the shaping circuits nonconductive, the gain of the system corresponds to the open loop gain of the amplifier 34. This would result in the development of the steepest slope possible for the overall system. The inclusion of resistor 95 limits the maximum single segment slope to a more useful and calibrated value. A resistor 99 connected between switch blade 56j and ground serves as a balancing resistor at the positive input of the differential amplifier for the resistor 95.

It should also be noted that with switch 50 in its alternate position, translating circuit 8i) shifts the composite curve horizontally, while translating circuit 74 shifts the composite curve vertically. This is due to the fact that now the D-C component from translating circuit 80 is added to the input signal IIN to which the differential amplifier 34 responds directly, while the D-C component from translating circuit 74 is added to the output signal IOUT, or a portion thereof, as it is fed back to the differential ampliiier. Translating circuit l80 is switched between the two inputs of the differential amplifier for the two modes of operation, simply for the purpose of balancing.

Experience has indicated the need to limit the magnitude of the output current IOUT with respect to both its minimum and maximum magnitudes. Moreover, the output limiting means should be arranged to hold the output current, as distinguished from the output voltage, within a desired range, because the output load rnay be anything up to 600 ohms, and voltage limiting would give different results for different loads. This feature of output current limiting is provided by the circuit elements now to be described.

The current through a load, represented by a resistor 130, is controlled by comparing the voltage at output terminal 42b with two reference voltages. The two reference voltages are developed by an adjustable voltage supply 141) shown within dotted lines in FIGURE 1B. Supply 140 includes a Zener diode 142 connected to a resistor 144 which, in turn, is connected to a source of positive potential. A rst diode 146 and a first potentiometer 148 form a rst branch connected in parallel with Zener diode 142, while a second potentiometer 150 and a second diode 152 form a second branch connected in parallel with the Zener diode. The voltage on wiper arm 148g of potentiometer 148 serves as one reference' voltage and controls the upper limit of the output current, while the voltage on wiper arm th: of potentiometer 150 serves as the second reference voltage and controls the lower limit of the output current.

The circuitry for controlling the upper and lower limits of the output current is shown Within the dotted lines 110 in FIGURE 1B. This circuitry includes three

transistors

112, 114 and 116. A resistor 118 is interposed between the base electrode of transistor 112 and the emitter electrode of transistor 114. The emitter electrode of transistor 114 is connected to the output terminal 42b by means of a conductor 120. The collector electrodes of

transistors

112 and 116 are connected together and connected to resistor 132 in the output amplifier 40 by means of a conductor 122. The emitter electrode of transistor 112 is connected to wiper arm 148:1 by means of a conductor 124, while the base electrode of transistor 114 is connected through a resistor 126 to wiper arm 150:1.

So long as the reference voltage on wiper arm 148a is more positive than the voltage at output terminal 42b, transistor 112 is back biased and nonconductive. When the voltage at output terminal 42b exceeds the reference voltage at wiper arm 145er, as when the output current in- Cir Cal

creases beyond a prescribed level, transistor 112 is rendered conductive and current is drawn through conductor 122 to transistor 112. This action prevents the voltage across resistor 132 from increasing, thus limiting the output current from amplifier 46. The wiper arm 148a is set to a position which will result in the desired upper limit of the output current.

So long as the voltage at output terminal 42b is more positive than the reference voltage on wiper arm 150a, transistor 114 is back biased and nonconductive. Therefore, no voltage drop is developed across a resistor 127 connected to the collector electrode of transistor 114. The voltage across resistor 127 serves as the bias voltage for transistor 116. When the voltage across resistor 127 is zero7 transistor` 116 is nonconductive. W'hen the voltage at output terminal 42b is less than the reference voltage at wiper arm 15051 as when the output current decreases to a point below a prescribed level, transistor 114 is rendered conductive. A voltage drop is then developed across resistor 127 which causes transistor 116 to conduct and supply current to resistor 132. This action prevents the voltage across resistor 132 from decreasing thus maintaining the output current from amplifier 40 above the prescribed limit. The wiper arm 1S0a is set to a position which will result in the desired lower limit of the output current.

Capacitors

128 and 129 are included in circuit to prevent high frequency oscillations.

Among the advantageous features of the disclosed apparatus is the ease with which the adjustments may be set to simulate a desired function. In setting the slope and starting point potentiometers for a particular segment of the desired function, the adjustments do not affect previously set segments. Thus, back-and-forth adjustments and calibrations, a common problem of some presently available function simulators, are avoided.

It should also be noted that the present invention is not limited lo simulating functions having only one change in slope such as in the curve illustrated in FIGURE 2. Rather, the present invention has such versatility and flexibility as to render it capable of developing transfer characteristics having two or more changes in slope, such as in S curves and the like.

Although the graphs representing the transfer characteristics of the shaping circuits are illustrated as straight lines throughout their entire lengths, in practice, the initial portions are slightly curved due to the nonlinearity of the transistors in the shaping circuits. As a result, the individual segments of the' transfer characteristics actually join one another with a smooth, rounded transition, rather than with a sharp, angled transition as shown in the drawing. This smooth transition is advantageous in that the simulated transfer characteristic generally more nearly approximates the desired characteristic.

While there have been described what are at present considered to be the preferred embodiments of this invention it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed to cover all such changes and modifications as fall within the true' spirit and scope of the invention.

What is claimed is:

1. Circuitry having an adjustable transfer characteristic comprising:

means for supplying an input signal;

a plurality of shaping circuits each having a transfer characteristic represented by a straight-line graph, the slope and starting point of which are adjustable and the slopes of all said straight-line graphs being of the same sign;

a differential amplifier;

means for selectively coupling the outputs of said shaping circuits to the two inputs of said differential amplifier to combine said transfer characteristics, the selection of the' input of said differential amplifier to which any shaping circuit is to be connected being dependent upon the desired sign of the straight-line graph of that shaping circuit;

means coupled to the output of said differential amplifier for developing a feedback signal;

and means for switching the' inputs of said shaping circuits between said input signal means and said feedback signal means, said switching means coupling said feedback signal to one of said inputs of said differential amplifier when said inputs of said shaping circuits are switched to said input signal means and said switching means coupling said input signal to one of said inputs of said differential amplifier when said inputs of said shaping circuits are switched to said feedback signal means.

2. Circuitry having an adjustable transfer characteristic comprising:

means for supplying an input signal;

a differential amplifier;

means for selectively coupling the outputs of said shaping circuits to the two inputs of said differential amplifier to combine said transfer characteristics, the selection of the input of said differential amplifier to which any shaping circuit is to be connected being dependent upon the desired sign of the straight-line graph of that shaping circuit;

means coupled to the output of said differential amplifier for developing a feedback signal and for coupling said feedback signal to one of said inputs of said differential amplifier;

and means -for coupling said input signal simultaneously to the inputs of all said shaping circuits.

3. Circuitry having an adjustable transfer characteristic comprising:

means for supplying an input signal;

a plurality of shaping circuits each having a transfer characteritsic represented by a straight-line graph, the slope and starting point of which are adjustable and the slopes of all said straight-line graphs being of the same sign;

a differential amplifier;

means for selectively coupling the outputs of said shaping circuits to the two inputs of said differential amplifier to combine said transfer characteristics, thfl selection of the input of said differential amplifie. to which any shaping circuit is to be connected being dependent upon the desired sign of the straight-line graph of that shaping circuit;

means coupled to the output of said differential amplifier for developing a feedback signal and for coupling said feedback signal simultaneously to the inputs of all said shaping circuits;

and means for coupling said input signal to one of said inputs of said differential amplifier.

4. Circuitry having an adjustable transfer characteristc comprising:

means for supplying an input signal;

a plurality of shaping circuits each having a transfer characteristic represented by a straight-line graph, the slope and starting point of which are adjustable;

means for adding together the outputs of said shaping circuits to combine said transfer characteristics;

means coupled to the output of said adding means for developing a feedback signal;

and means for switching the inputs of said shaping circuits between said input signal means and said feedback means, said switching means coupling said feedback signal to the input of said adding means when said inputs of said shaping circuits are switched to said input signal means and said switching means coupling said input signal to said adding means when said inputs of said shaping circuits are switched to said feedback means.

5. Electronic apparatus providing an adjustable transfer characteristic, comprising:

a plurality of shaping circuits connected in parallel to receive an input signal and each 'having an operating transfer characteristic represented by a straight-line graph;

means forming part 0f each shaping circuit providing an adjustment of the slope and starting point of the corresponding straight-line graph;

a high-gain amplifier having a negative feedback circuit and serving to produce an output signal representing the sum of all signals supplied to the input of the amplifier; and

circuit means coupling the outputs of said shaping circuits to the input of said amplifier to produce an output signal refiecting the combination of said transfer characteristics, said circuit means including means selectively settable for combining each shaping circuit output either additively or subtractively.

6. Apparatus as claimed in claim 5, wherein said amplifier comprises a differential amplifier having two input terminals; said settable means including switch means selectively operable to connect the output of any shaping circuit to either of said two input terminals, whereby to combine the corresponding signal either additively or subtractively.

7. Apparatus as claimed in claim y6, wherein the switch means includes means to connect balancing impedances to said amplifier input terminals to match any selected set of connections from said shaping circuits and maintain an overall balance between the two input terminals.

8. Apparatus as claimed in claim 5, including adjustable signal-producing means for producing a steady signal of adjustable magnitude; and means connecting said signalproducing means to the operating circuits of said apparatus to shift the combined transfer characteristic curve, as a unit, to a desired location with respect to reference coordinates.

9. Apparatus as claimed in claim 8, wherein the output of said signal-producing means is connected to the input of said amplifier.

10. Apparatus as claimed in claim 8, wherein the output of said signal-producing means is connected to the inputs of said shaping circuits.

11. Electronic apparatus providing an adjustable transfer characteristic, comprising:

a high-gain amplifier;

a plurality of shaping circuits connected in parallel between the output and input of said amplifier to provide a negative feedback signal responsive to the combined transfer characteristics of all of said shaping circuits, each shaping circuit having a transfer characteristic represented by a straight-line graph;

means forming part of each shaping circuit providing an adjustment of the slope and starting point of the corresponding straight line graph; and

means for supplying an input signal to the input of said amplifier so as to produce a corresponding output signal refiecting the combined transfer characteristics of said shaping circuits.

12. Apparatus as claimed in claim 11, including selectively settable means for coupling the outputs of said shaping circuits individually either additively or subtractively with respect to the other shaping circuit outputs, so as to provide the desired effect on the overall transfer characteristic.

13. Apparatus as claimed in claim 11, including a resistive negative feedback circuit forsaid amplifier, whereby to limit the maximum single segment slope to a useful calibrated value.

14. Apparatus as claimed in claim 11, including a-djustable signal-producing means for producing a steady 11 signal of adjustable magnitude; and means connecting said signal-producing means to the operating circuits of said apparatus to shift the combined transfer characteristic curve, as a unit, to a desired location with respect to reference coordinates.

15. Apparatus as claimed in claim 141, wherein the ouptut of said signal-producing means is connected to the input of said amplifier.

16, Apparatus as claimed in claim 14, wherein the output of said signal-producing means is connected to the inputs of said shaping circuits.

17. Electronic apparatus responsive to an input signal for producing an output signal in accordance with an adjustable non-linear transfer characteristic, comprising:

a high-gain amplier; a plurality of shaping circuits each having a transfer characteristic represented by a straight-line graph;

switch means operable between rst and second conditions;

said switch means in said first condition serving to direct said input signal to the inputs of said shaping circuits and to couple the combined outputs of sai-d shaping circuits to the input of said amplifier;

said switch means in said second condition serving to connect all of said shaping circuits between the output and input of the amplifier, to provide a negative feedback circuit with the selected non-linear transfer characteristics, and also serving to direct said input signal to the input of said amplifier together with the negative feedback signal.

References Cited UNlT ED STATES PATENTS 2,683,807 7/1954 Paxson 328-182 JOHN S. HEYMAN, Primary Examiner B. P. DAVIS, Assistant Examiner