US2769137A - Single bias voltage curve shaping network - Google Patents

Description

Oct. 30, 1956 OUTPUT CURRENT (MN-UANPERES) Filed Nov. 13, 1953 -oo-o-M'EAsuREn CURVE COMPUTED CURVE 1 I l l l O 4 8 l2 I6 20 INPUT VOLTAGE (VOLTS) I INVENTOR. MELVTLLE c. CREUSERE ATTORNEYS United States Patent SINGLE BIAS VOLTAGE CURVE SHAPING NETWORK Melville C. Creusere, China Lake, Calif., assignor to the United States of America as represented by the Secretary of the Navy Application November 13, 1953, Serial No. 392,061

3 Claims. (Cl. 32374) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to curve shaping networks and in particular to a single bias voltage curve shaping network which produces an electrical current which is a predetermined nonlinear function of the input voltage.

Curve shaping networks are particularly useful in D. C. computing circuits of analogue computers for producing a D. C. current which is a predetermined function of the input voltage, or current.

Previously known curve shaping networks require the use of a plurality of different valued bias voltages, which are generally obtained by means of a bleeder string of resistors. The disadvantages in using a bleeder string of resistors to obtain the desired values of the bias voltages lie in the power requirements necessary to provide the necessary current flow through the string and in the problem of dissipating the heat developed by the bleeder string. Heat dissipation is a serious problem particularly in electrical equipment designed for use in aircraft.

It is, therefore, an object of this invention to provide a curve matching diode network that requires a single bias voltage.

It is a further object of this invention to provide a curve matching network which requires a single bias voltage and which produces a D. C. current which is substantially a predetermined nonlinear function of the input voltage.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. 1 is a wiring diagram of the invention;

Fig. 2 is a graph of the output current of the curve shaping network as a function of the input voltage.

In Fig. 1, input terminal of the curve shaping network is adapted to have applied to it a positive D. C. input voltage, Em. Ein is applied across a string of resistors 12, 14, 16, 18 which are connected in series. Terminal 20 of the string is connected to ground. Shaping branch 22 consists of resistor 24 and diode 26 connected in series, and has one terminal of the branch connected to terminal 28 between resistors 12, 14. Shaping branch 30 consists of resistor 32 and diode 34 connected in series and has one terminal of the branch connected to terminal 36 which is located between resistors 14 and 16. Shaping branch 38 consists of resistor 40 and diode 42 connected in series, and has one terminal of the branch connected to terminal 44 which is between resistors 16 and 18. The other terminal of each of the shaping branches 22, 30, 38 is connected to a common terminal 46. A Single source of bias potential 48, such as a battery, is also connected to terminal 46 in such a 2,769,137 Patented Oct. 30, 1956 manner that the potential of terminal 46 is above ground potential. Diodes 26, 34, 42 are connected to permit current to flow from terminals 28, 36 and 40, respectively, to terminal 46. Diodes 26, 34, 42 may be vacuum diodes or crystal diodes, and among crystal diodes there is a choice between point contact germanium diodes, junction germanium diodes, junction silicon diodes, etc.

The current flow iout, through resistor 18 can be made a predetermined function of the input voltage, Em, by the proper choice of the values of resistance of the resistors in the network and by the value of bias voltage Eb obtained from source 48.

Referring to Fig. 2, the dotted curve is a graph of Eq. 1. I

l out 2.2374 lOge 0.747 Ein computed from the above equation. The solid line is the graph of font vs. Em as obtained from the network of Fig. 1.

Assuming that diodes 26, 34, 42 have perfect characteristics; i. e., infinite back resistance and zero forward resistance, the current flow, l out, through resistor 18 is zero when input voltage Eln is zero. As Ein increases the current flow in resistor 18 is determined by the sum of the resistances of resistors 12, 14, 16 and 18. Initially the curve of iout vs. Em is a straight line having a slope determined by the resistance of the sum of resistors 12, 14, 16 and 18. This is true until the value of Ein reaches a magnitude at which the potential of terminal 28 equals Eb at which time diode 26 begins conducting a certain quantity of current around resistor 18, and causes font, to increase more slowly as Eln increases. The graph of l out. vs. Em for Em greater than that necessary to cause the potential at terminal 23 to exceed E1; is a straight line segment having a different slope from the initial straight line. The value of En at which diode 26 commences conducting is a break point of the curve. A second break point occurs when Em has obtained a magnitude which will raise the potential of terminal 36 to a point where it equals Eb, and a third break point occurs when Em has reached a still greater magnitude at which terminal 44 equals Eb. As each break point is reached the subsequent straight line segment of the curve has a different, and in this example, a lesser slope than the preceding segment.

Since the derived values of font and Em at the break points are known, and the slopes of the line segments forming the curve are also known, as well as the potentials at the nodes 28, 36, 44, when the shaping branches connected to the respetcive terminals begin to conduct, it is possible by straight forward electrical circuit theory to determine the values of the resistors in the network. As the number of line segments, or the number of shaping branches, is increased the accuracy with which a given curve can be matched is improved.

In the above discussion it was assumed that diodes 26, 34, 42 had an infinite back resistance and a Zero forward resistance, and on that basis the curve of font Vs. Em for the network would consist of a series of connected straight line segments. A different curve but still one which consists of a series of straight line segments will result if both the forward and back resistance characteristics of the diodes are considered to be finite values greater than zero. However, since the resistance characteristics of the diodes are actually nonlinear in both the forward and back direction, the out vs. Em curve will consist of segments which are curved to an extent dependent on the relative magnitudes of the forward and back resistances of the diodes as compared to the network resistances. The effect of diode nonlinearity is to round off the corners of the segments of the curve and actually aids in obtaining a curve that is closer to the desired curve. In synthesizing the values of the components of the circuit the values of the forward and back impedance of the diodes must be considered in order to obtain. accurate results.

The solid curve of Fig. 2 is agraphof. the output current iout as a function of the input voltage Em for the circuit of Fig; lin which the components of the circuit are as follows:

Resistor 12-, 6K ohms- Resistor 14, 45K ohms Resistor'16, 1.5K ohms- Resistor 18, 6K ohms Resistor 2.4, 5.5K ohms Resistor 32, 5.0K ohms Resistor 40', 3 5K ohms Diodes 26, 34, 42, G. E. 4JA1A1 junction diodes Bin, to 18 volts El), 3 volts The maximum error between the theoretical. values and the actual values as determined from the circuit has a maximum error of 5% and an average error of approximately 1% over an input range of Em of from 3.5 to 17.5 volts.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, tobe understood that within the scope of the appended claims the invention. may be practiced otherwise than as specifically described.

What is claimed. is:

l. A curve matching network comprising a plurality of resistors connected in series to form a string, said string adapted to have applied thereacross a D. C. input voltage, a plurality of shaping. branches connected in the network, each branch having two terminals, each branch being comprised of a precision resistor of calculated value and current rectifying means connected in series, one terminal of each branch connected to but a single terminal between resistors of said string, the other terminal of each branch being connected to a common terminal, a source of D. C. bias potential directly connected to said common terminal, said current rectifying means in each branch connected so as to permit current to flow only in the same direction in each of the branches, the values of said resistors being such that the magnitude of the D. C. current through one of the resistors of said string is substantially a predetermined. nonlinear function of the input voltage.

2. A curve matching network comprising a plurality of resistors connected in series to form a string and having two terminals, said string adapted to have a D. C. input voltage applied to one of the terminals of the string, the other terminal adapted to be grounded, shaping branches, the number of shaping branches being one less than the number of resistors in said string, each of said shaping branches having two terminals and: comprising a resistor and current rectifying means connected in series, one terminal of each branch being connected to different terminals between pairs of resistors in said string, the other terminal" of each branch being connected to a common terminal, a source of substantially constant D. C. bias potential connected between said common terminal and ground, said current rectifying means in each branch connected to permit current to flow toward. said common terminal, said sources of, D. C- potential connected to keep said common terminal at a potential above ground, the values of the resistors in said network being such that the D. C. current through the resistor of said string nearest tothe ground terminal of said string is substantially a predetermined function of the input voltage.

3 A curve matching network comprising a plurality of resistors connected in series to form a string and having two terminals, said string adapted to have a D. C- input voltage applied to one of the terminals, the other terminal adapted to be grounded, shaping branches, the number of shaping branches being one less than the number of resistors in said string, each of said shaping branches having two terminals and comprising a resistor and current rectifying means connected in series, one terminal oi each branch being connected to d-ilierent terminals between pairs of resistors in said string, the other terminal of each branch being connected to a common terminal, a source of substantiaily constant D. C. bias potential connected between said common terminal and a ground terminal, said current rectifying means in each branch connected so as to permit current to flow only in the same direction in each of the branches, the values of the resistors in said network being such that the D. C. current through the resistors of said string nearest to the ground terminal of saidstring is substantially a predetermined function of the input voltage.

References Cited in the file of this patent UNITED STATES PATENTS 2,104,336 Tuttle inn. 4, 1933 2,680,230 Garrison ct ai. June 1., l54 2,697,201 Harder Dec. 14-, 1954

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