US3416152A

US3416152A - Analog-to-digital converter

Info

Publication number: US3416152A
Application number: US361916A
Authority: US
Inventors: Theodore R Trilling
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-04-22
Filing date: 1964-04-22
Publication date: 1968-12-10
Anticipated expiration: 1985-12-10

Description

Dec. 10, 1968 T, R, TRILUNG 3,416,152

ANALOG -TO-DIGI'I'AL CONVERTER Filed April 22, 1964 2 Sheets-Sheet 2 J59 54 5a AMPLlFlER 2 55 VERTICAL ANALOG DEFLECTION SIGNAL SWEEP CLOCK VOLTAGE PULSE GENERATOR GENERATOR F' 3 l LOGIC GATE 74 v 71 1 L-' C OUTPUT I v ghifi ANALYZER b n n rl [3 n r1 64 73 c V dc} M e fl l'U"U'l f1: f "E Fig 5 Fig 6 B1 84 F lg. 4

SWEEP souRcE VOLTAGE PULSE l LOGIC GATE INVENTOR. F lg, 8 THEODORE R. TRILLING [WE/2A ATTORNEYS United States Patent 3,416,152 ANALOG-TO-DIGITAL CONVERTER Theodore R. Trilling, 15 Hunt Road, Levittown, Pa. 19056 Filed Apr. 22, 1964, Ser. No. 361,916 11 Claims. (Cl. 340347) ABSTRACT OF THE DISCLOSURE A cathode ray tube or solid state device is utilized in conjunction with any of a plurality of matrices on which a beam of carriers is impinged to thereby convert an analog signal to a series of digital outputs expressive of that analog signal depending upon the particular configuration of the matrix and the control circuitry utilized to deflect the beam of carriers.

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.

The present invention relates to analog-to-digital converters and more particularly to a cathode ray tube and solid state device utilizing a matrix on which a beam. of carriers is entrained to convert an analog signal to a series of digital outputs expressive of that analog signal.

It is desired in many applications to convert an analog signal of various kinds into a digital output of various kinds, for example, into a pulse train wherein either the width of the pulse, the height of the pulse, or the sequence of a series of pulses is indicative of the height of the analog signal at that instant. For example, it may be desired to convert a voice signal into a series of pulses trains for the purpose of coding. Or it may be desired to have a series of outputs, each output being indicative of a certain height of the incoming analog signal. Prior art devices in this cfield have shared the common failing of not being fast enough. For example, an attempt to break up a voice signal into a digital form may achieve only conversion of the low frequency components of the voice with substantial distortion of the voice signal or garbling of the message.

The present invention provides a very high speed means for converting an analog signal to a digital signal wherein the digital increments of signal comprise a small part of each cycle even at the highest frequencies present. To attain this, the invention provides a cathode ray tube wherein the analog signal is inserted on one or both of the deflecting means and a matrix of conducting spots are placed on the face of the tube and are connected to issue an output current upon incidence of a beam from the electron gun of the tube. The invention also provides a solid state device which is an equivalent of a cathode ray tube, in which a beam of carriers is issued through the solid state device to a matrix of collector spots on one face of the solid state device. The cathode ray tube and solid state device of the present invention have been discovered to be extremely versatile and are usfeul for a number of associated devices in addition to the translation of a voice signal into a pulse train. Others may be mentioned, such as a shaft encoder, phase comparator, delay line, multiplex discriminator, and other uses, as will appear.

Accordingly, it is an object of the present invention to provide a cathode ray tube with a matrix of conducting spots on the inside face of the tube with the digital output of the tube being a function of the analog input.

Another object of the invention is to provide a solid state device having therein a beam of carriers on the collector matrix thereof with the digital output of the Ice matrix being a function of an analog input into the device.

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

FIG. 1 shows a view in section of a cathode ray tube according to the invention;

FIG. 2 shows a view in section of a solid state device according to the present invention;

FIG. 3 shows a schematic diagram of an analog-todigital converter circuit of the present invention using either the cathode ray tube of FIG. 1 or the solid state device of FIG. 2;

FIG. 4 shows a detail of a matrix of an embodiment of the invention with an associated output amplifier;

FIG. 5 shows another embodiment of the invention comprising a pulse height analyzer;

FIG. 6 shows typical waveforms in the outputs of the embodiment of FIG. 5;

FIG. 7 shows another embodiment of the invention comprising a pulse delay line;

FIG. 8 shows a typical waveform in the output of the embodiment of FIG. 7;

FIG. 9 shows a further embodiment of the invention comprising a phase comparator;

FIG. 10 shows another embodiment of the invention comprising a multiplex discriminator;

FIG. 11 shows another embodiment of the invention comprising a shaft encoder for determining the angular position of a shaft and producing a digital output in response thereto;

FIG. 12 shows a shaft whose angular position is desired to be expressed in the shaft encoder of FIG. 11; and

FIG. 13 shows the construction of a matrix spot and lead of the cathode ray tube of FIG. 1.

Turning now to the drawings, FIG. 1 represents a cathode ray tube 21 which is conventional except for the target area. A cathode 22 emits a stream of electrons which is controlled by a grid 23 and focused by a focusing ring 24 on a plate 25 which in this case is the matrix of the invention. Cathode 22, grid 23 and focusing ring 24 comprise an electron gun issuing a beam of electrons 26 onto the plate 25. A voltage supply, not shown, is provided between the cathode 22 and the plate 25, placing plate 25 at a very high positive voltage relative to the cathode 22. The construction of the cathode ray tube is not shown in detail because cathode ray tubes are known in the art, and the construction of this cathode ray tube is well known in the art except for the plate comprising the matrix of the present invention. Also, are shown deflecting plates 27 across which a voltage is placed to deflect the beam in order to place it in the desired position on the matrix 25. Another pair of deflectirig plates may be placed perpendicularly to the shown pair 27 for horizontal as well as vertical deflection. It will be understood that although electrical deflection means are shown, electromagnetic deflection may also be used, which would constitute a pair of coils placed across the tube. The choice of electrical or electromagnetic deflection means will depend on the amount of precision and the amount of speed of the deflection which is desired. In general, the electrical means provides greater speed of response to an analog signal, while the electromagnetic means provides higher precision. For high frequency responses one would generally select electrical deflection means, but for precision work one would generally select electromagnetic deflection means.

In FIG. 2 is shown a solid state equivalent of the cathode ray tube. The device comprises an emitter 31,

base 32, intrinsic core 33 and collector spots 34. The emitter 31 is composed of a doped semiconductor material providing polarity in one direction, either N or P type material. The base 32 will be of the opposite polarity, as is understood by persons in the art. The core 33 is a pure intrinsic semiconductor material that is not doped either N or P type. The collector spots 34 will be doped into the face of the opposite end of the core 33 and will be of the same polarity as the emitter 31. A voltage supply 35 is connected between the collectors 34 and the emitter 31. A bias voltage 36 is provided between the base 32 and the emitter 3 1. The polarity of these voltage supplies will depend upon the polarity of the

semiconductor elements

31, 32 and 34, as will be understood by a person in the art. A stream of carriers will issue from the emitter through the base and through the intrinsic core to contact the collector matrix 34. This beam of carriers, which may be either holes or electrons, depending on the chosen polarity, may be focused by a focusing ring 37. The beam may also be deflected by a pair of deflecting plates 38. It will be understood that plates may be provided both horizontally and vertically for horizontal and vertical deflection. It will also be understood that cit-her electrical means or electromagnetic means may be provided as in the cathode ray tube of FIG. 1. The outputs from the collector spots 34 which form the matrix of the device, Will be led through a set of logic circuits with an output indicator indicated generally at 39. \This output indicator may either be a set of dials giving a digital expression of the signal or it may be in the form of a connection to another part of the circuit providing a pulse train expressing the digital signal. It will be seen that the solid state device of FIG. 2 is generally useable for all of the uses of the cathode ray tube of FIG. 1.

The operation of the converter may be illustrated by reference to MG. 3, in which is shown a matrix 51 on an end plate 52 of the converter. The analog signal 53 is fed into the vertical deflection means 54 which places a voltage proportional to the analog signal across the vertical plates 55 to deflect the beam up and down on the matrix 51 in accordance with the analog signal. A sweep voltage generator 56 causes a horizontal voltage on horizontal deflection plate 57 which causes the beam to pass across the tube at a relatively slow rate and then revert to the first side of the beam at a relatively fast rate in response to a pulse from a clock pulse gen erator 58. A voltage causing the beam to sweep horizontally across the tube may be either a sawtooth voltage or a staircase voltage depending upon the application. Because of the simultaneous application of the sweep voltage and the analog signal fed into the vertical deflection means, the position of the beam at various points in the matrix at various points in time will produce an output which is a pulse train or a series of pulse trains which are a reflection of the analog signal fed into the converter. These pulse trains may be fed into an amplifier 59 and the amplified signal fed to a logic gate 60 into which may be optionally fed also a series of clock pulses from clock pulse generator 58 for the purpose of sampling the pulse train. When used in this manner, the logic gate 60 wil be of the and gate type. "The output from logic gate 60 will be a sampled pulse train, the incidence of which is indicative of the analog signal.

FIG. 4 illustrates a specific matrix which may be used in the converter as shown in FIG. 3. A matrix 61 is arranged in a code called a Gray code. This matric will be in the case of the cathode ray tube a printed layer on the inside of the face of the tube and in the case of the solid state device will be a continuous arrangement of doped collector material on the end of the intrinsic core with a layer of metallic material laid directly over the doped collector material. It will be seen that there will be a current out of the matrix when the beam of carriers either in the tube or solid State device contacts some conducting portion of the matrix. It will also be seen that as the beam sweeps across the matrix, the arrangement of conducting and nonconducting portions of the matrix at that level is unique to that level, so that the output train of square pulses will be a unique output for the particular level of the analog signal at that point. The Gray code shown provides code levels, and a matrix of 100 levels as shown would typically be reduced to a printed metal matrix on the inside face of the cathode ray tube approximately one inch high. In a cathode ray tube of approximately four inches by four inches operating area there Would be room for approximately 300 levels of signal. The matrix would be approximately one-tenth of an inch wide and across the face of the tube there would be room for approximately 30 successive matrices. One sweep of the voltage across the tube would, therefore, give 30 successive coded outputs of the analog signal. In this code it is important that the repetition of bits or code readings from the matrix be at least ten times the highest frequency of the analog signal desired to be analyzed. For an analog signal corresponding to a voice input where the highest frequency is approximately five kilocycles to ten kilocycles, a typical sampling rate would be 100,000 hits per second. Since a typical number of matrices on the face Of the tube might be 25, this requires a sweep frequency of 4,000 sweeps per second. These are examples, and for other uses other parameters would be chosen. In this embodiment all of the matrices would be tied together at their tops and a single output would be led out to an amplifier 59 which in this embodiment comprises a transistor 62 connected to a minus source of voltage, in which the output 63 appears across a load resistance 64. The output of this embodiment as shown would be in the form of a pulse width modulated train of pulses in which the width of the pulses and their position would determine the code level. LIf desired, the pulse width modulated code may be translated to a pulse code modulated code by the insertion of a clock pulse from clock pulse generator 58. There would be an inserted clock pulse during each occurrence of a square pulse or nonpulse on the matrix 61. This converts the pulses of variable width to a series of pulses of equal width with position of pulse only being indicative of the level of the signal. The Gray code selected and shown in RIG. 4 is one which provides a minimum number of changes of position from one level to the next. One may instead use a. binary code, or one may take a random code in order to provide a pulse train indicative of a voice signal which can only be translated back into a voice signal by one having a copy of that code. Another variation on this general theme would be a matrix arranged in the Morse code wherein the signal input is a series of voltage levels corresponding to various letters in which the output automatically translates the letter input into the corresponding dot-dash code.

FIG. 5 shows an embodiment of the invention which is known as a pulse height analyzer. In this embodiment, there is no sweep voltage. An analog signal 71 is placed on vertical deflection plates 72. A matrix comprising a single column of conducting spots 73a-f is placed on the converter and each of the spots is separately connected to an output analyzer 74. The analog signal will cause the beam to ride up and down on this single column 73 without moving horizontally. The result will be a number of outputs equal to the number of spots in the column, wherein the width of the pulse in each output is dependent upon the amount of time that the analog signal dwells in the vicinity of that spot. The outlay analyzer 74 may be a logic store or computer memory or an indicator, since the output is already pulse height analyzed. If the input is a switching address, the output will be a series of currents to a series of loads to be turned on and off in response to the address. In this embodiment, the tube is a switching tube. This can be extended to a two-dimensional matrix.

Although six spots are shown in the matrix of FIG. 5, it will be understood that potentially hundreds of separate levels may be set forth in a column on the face of a tube. It is important also to note that in this embodiment the spots on the face of the tube are not connected together as in the code matrix of FIG. 4, but each lead must be led separately out of the tube and into the analyzer. The manner in which this is done is shown in FIG. 13, to be described below.

In FIG. 7 is another embodiment of the invention identified as a pulse delay line. In this embodiment a sweep voltage 81 is applied across a pair of deflection plates 82. A matrix 83 on the face of the tube consists of a single row of spots 8341-7 and there will be an output from each as the beam sweeps across it. The sweep voltage 81 is triggered by a source pulse 84 which may also send the same pulse to a logic gate 85. One or more output pulses from matrix 83 may be selected by a selector switch 86 which sends the selected output pulse or pulses to the logic gate 85. In this embodiment, logic gate 85 is of the or type. The pulse delay line of this embodiment has a number of applications. It may be, for example, desired to have an input pulse followed by a certain period of time by a second pulse. This is commonly used in radar in connection with a ranging device. In another application one may have a series of voltage inverters in a stepped wave voltage output power supply, and it may be desirable to operate the voltages out of phase with each other by a predetermined amount. By connecting the inverters of the various voltage supplies to diflferent outputs from the matrix 83 and triggering the entire assembly by a single oscillator input to sweep voltage 81, it will be seen that there is provided a series of output pulse trains of the same frequency as the input and out of phase with each other by a predetermined amount dependent upon the separation of the spots in the matrix from each other. The timing of the pulse outputs may also be finely adjusted by varying the rate of rise of the sweep voltage 81. This provides a fine adjustment, whereas the selection of the particular outputs will provide a coarse adjustment. In another application one may wish to delay an input train of pulses by a certain amount in order to synchronize this train of pulses with another frequency. In this application, the source pulse would be fed to the sweep voltage 81 only and not to the logic gate 85. FIG. 8 shows a typical waveform from the delay line of FIG. 7 wherein 91 is the input pulse and 92 is the output pulse delayed from pulse 91 by delay time T FIG. 9 shows still another embodiment of the invention, this one comprising a phase comparator. Two sine waves 1; and f of the same frequency are desired to be compared to determine the relative phase angle between them. The two sine waves are placed across the pairs of

deflection plates

101 and 102, respectively. The matrix 103 of the embodiment includes a column of dots bisecting the center of the face. Extending horizontally on each side of each dot is a line of conducting material, and each dot and each line have separate outputs leading to output logic circuits and readout 104. The output logic circuits receiving the outputs from the various lines and dots on the face of the converter determine three significant values: A, the upper dot contacted by the beam, B the uppermost line contacted by the beam, and B, the lowermost line contacted by the beam. The logic circuits will also be capable of determining in what order these three values occur. The logic circuits in themselves are standard digital logic circuits and are not shown here. From the basic mathematical characteristics of an ellipse formed by two sine waves, the phase angle between the two sine waves may be calculated from the following relationship:

sin 0:B/A

If B is on the right side and B is on the left side, as shown, the readout will indicate an angle in the first or fourth quadrant. It is also known that if the order of the three values is counterclockwise, the angle is in the first quadrant. If the order of the values is clockwise, the angle is in the fourth quadrant. Likewise, if the angle may be in the second or third quadrants, it will be in the second quadrant if the order of the values is counterclockwise and in the third quadrant if the order of the values is clockwise. Readout 104, after making appropriate digital calculations, will express the calculated angle between the two sine waves. It will be understood that the number of levels on the face of the converter may be several hundred instead of the limited number shown in FIG. 9.

In FIG. 10 is shown another embodiment of the invention, this one comprising a multiplex discriminator. A multiplex signal 111 to be discriminated and a sweep voltage 112 are placed across the

deflection plates

113, 114, respectively, of the converter. A matrix 115 comprises a series of vertical channels, ae. Multiplex signal 111 will consist of bits of information taken consecutively from a number of sources, in this example five, and it is desired to separate the bits of information from the five sources and send them into five separate outputs. Sweep voltage 112, which in this case preferably will be a staircase voltage dwelling momentarily on each column, will be synchronized to return to column a at the completion of five steps so that it distributes bits of information consecutively across the columns a-e. Each channel ae will then represent the output from one source. All of the output lines are led separately out of the converter, and the output lines for each channel a-e are fed separately out to the selector 116 which sends each of these channel outputs to a separate recorder 117, which may be a logic store or computer memory. Each of these outputs is already pulse height analyzed, and available immediately for further use.

FIG. 11 shows still another embodiment of the invention comprising a shaft encoder. It is desired to find the angle by which a shaft 121 shown in FIG. 12, such as the azimuth bearing of a radar transmitter, varies from a zero reference level. Electromagnetic means, not shown, may be attached to the shaft itself to give a pair of signals proportional to the sine and cosine of the angle to be detected. These are applied as shown in FIG. 11 to deflecting

plates

122 and 123, respectively. A matrix 124 comprises in this embodimeint a circular series of pieshaped segments around the center of the face. Each pieshaped segment has a line leading separately to a readout comprising typically a lamp and an output signal to other circuits. When the sine and cosine of the desired phase angle are applied to the vertical and horizontal deflection plates, the electron beam will be deflected to contact one segment or possibly two. This will cause a lighting of the appropriate light in the readout circuit 125 and a signal on the appropriate line out.

The construction of the spots on the inside of the face of the cathode ray tube is shown in FIG. 13. A spout 131 of metal in the form of a thin film is deposited on the inside of the glass face 132 of the tube and a line 133 is extended out of the tube directly through the face of the tube. Before the metal spots are deposited, however, a high resistance film 134 is deposited on the inside of the glass face. The purpose of this is to provide a leakage path for any electrons which do not contact a conducting part of the matrix. This material is of carbon or tin oxide or various other high resistance films. It will be understood that this material is not regarded as a conducting material. Its resistance per unit length is in the order of thousands of times the resistance of the conducting spots. Its purpose is to prevent a build-up of electrons on the inside face of the glass which, if continued for a long enough time, would result in a high negative potential on the face of the tube and would stop the operation of the tube altogether. The leakage of the electrons on the face of the tube will be to the nearest metal conducting spot. This will cause a small level of noise on the output signal but this is so slight compared to the positive signals on the conducting spot upon incidence of the beam that no serious problem is encountered. It will be understood that the spots 131 may be in the form of circles, squares, lines or pieshaped segments, as shown in the various figures. It will also be understood that, although the cathode ray tube has been shown as constructed of glass, it may be constructed of ceramic material or, for that matter, it may be constructed of metal up to the face of the tube. Inasmuch as there is no visual output from the tube it is completely unnecessary to make the outer material of the tube transparent.

The construction of the solid state device may be made in a number of ways. A common method of making the device shown in FIG. 2 is to hollow out of one end of an intrinsic core a cylindrical shaft which is partly filled with semiconducting material of one polarity forming a base and then filled in over that with semiconducting material of the opposite polarity forming an emitter. Room is left for a leadout from the base and emitter. The collector spots on the opposite end of the intrinsic core may be deposited on the face of the core or may simply be doped into isolated areas of the face of the core itself. It is advisable to back the collector spots with metal and attach the outputs to the metal backing. This prevents a situation in which a carrier beam incident upon a collector spot might have to go a substantial distance through semiconductor material before contacting a low resistance path out. Such an occurrence would cause a substantial reduction in the output current and a loss of the sensitivity of the instrument.

It will be understood that the embodiments shown comprise only a few of the many uses for the tube or solid state device of the present invention. It will also be understood that various changes of the details, materials, steps and arrangement of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. A signal conversion apparatus comprising:

a means for providing a beam of carriers, said means including a solid state conversion device having an emitter composed of semiconducting material of one polarity, a base connected to said emitter composed of semiconducting material of the opposite polarity to said emitter and a carrier transit means composed of intrinsic semiconductor material connected to said base at one end;

a matrix means for receiving said beam of carriers and issuing an output current in response to incidence of said beam, said matrix including a collector of predetermined configurations of semiconducting material of the same polarity as said emitter and attached to said carrier transit means at the end opposite said base; and

a deflecting means for controlling the position of said beam on said matrix.

2. Apparatus as recited in claim 1 wherein:

said matrix means comprises a matrix of spots of conducting material, each of said spots being adapted to receive said beam and to conduct a current therefrom upon incidence from said beam; and

said deflecting means comprises first means to deflect said beam in response to an input signal to cause a spot in said matrix to conduct whereby the position of said conducting spot is a function of the amplitude of said input signal.

3. Apparatus as recited in claim 2 further comprising:

second means to deflect said beam in a direction perpendicular to said first means in response to a second input signal whereby the position of said conducting spot is a function of the amplitudes of both of said input signals.

4. Apparatus as recited in claim 3 wherein:

said matrix means is a code matrix comprising a conductive portion in a code pattern and a substantially nonconductive portion surrounding said pattern capable of drawing ofl electrons incident thereon;

said second means is an analog signal to be converted to a digital signal according to said code; and

said matrix means conducts an output current only during the time the beam contacts a conducting portion of said matrix.

5. Apparatus as recited in claim 3 comprising:

means to apply to said first deflecting means a signal proportional to a first sine wave;

means to apply to said second deflecting means a signal proportional to a second sine wave of frequency equal to said first sine wave;

said matrix including a center column of conducting spots each having an individual output line, said column bisecting the collector of said solid state conversion device and aligned with one of said deflecting means;

a pair of columns of conducting lines on each side of said center column and parallel therewith, the lines of each column extending perpendicularly to said center column and each line having an individual output line; and

logic means connected to all of said output lines to detect the spots and lines contacted by said beam and to express the phase angle between the two input sine waves as a function of said matrix outputs.

6. Apparatus as recited in claim 3 in combination with an azimuth bearing whose angular position is desired to be known comprising:

means to apply to said first deflecting means a signal proportional to the cosine of said angular position;

means to apply to said second deflecting means a signal proportional to the sine of said angular position;

said matrix comprising a series of radially extending lines around a center point of the collector of said solid state conversion device, one of which is contacted by said beam so as to be conducting; and

means to detect that line which is conducting and express it as the angular position of said bearing.

7. Apparatus as recited in claim 3 wherein:

said matrix comprises a succession of columns of spots, each column representing a single channel output;

said first means comprises a sweep voltage adapted to cause the beam to contact each channel in succession recurrently; and

said second means receives a multiplexed input signal comprising a series of bits taken in succession recurrently from a number of sources equal to the number of channels in said matrix;

whereby the output of each channel corresponds to the signal from one of said sources.

8. Apparatus as recited in claim 2 wherein:

said input signal is a variable sweep voltage adapted to cause the beam to pass recurrently across the collector of said solid state device;

said input signal being operable by an input pulse to cause the beam to return to a predetermined side of said matrix from which it sweeps across the matrix;

said matrix comprising a row of spots of conducting material successively contacted by said beam;

whereby the output from each spot is a pulse delayed in time from the input pulse by the time necessary for the beam to travel across the matrix from said predetermined side; and

means to select one of said outputs as a delay output pulse.

9. Apparatus as recited in claim 1 wherein said deflecting means comprises:

sweep voltage means to deflect said beam across said matrix recurrently in response to an input sweep signal; and

deflecting means aligned perpendicularly to said sweep means and adapted to deflect said beam in response to an analog input signal;

whereby the output of said matrix is a function of said input sweep signal and said analog input signal.

10. A signal conversion device comprising:

a cathode ray tube having a target face and an electron gun positioned at one end thereof for providing a beam of carriers;

first and second deflecting means for deflecting said beam of carriers;

a matrix means for receiving said beam of carriers and issuing an output current in response to incidence of said beam, said matrix means including a center column of conducting spots each having an individual output line, said column bisecting said tube face and aligned with one of said deflecting means, and a pair of columns of conducting lines on each side of said center column and parallel therewith, the lines of each column extending perpendicularly to said center column and each line having an individual output line;

means to apply to said second deflecting means a signal proportional to a second sine wave of frequency equal to said first sine wave; and

logic means connected to all of said output lines to detcct the spots and lines contacted by said beam and to express the phase angle between the two input sine waves as a function of said matrix outputs.

11. A signal conversion device comprising:

a matrix means for receiving said beam of carriers and issuing an output current in response to incidence of said beam, said matrix including a succession of columns of spots, each column representing a single channel output;

deflecting means including a first means having a sweep voltage adapted to cause the beam to contact each channel in succession recurrently and a second means for receiving a multiplexed input signal comprising a series of bits taken in succession recurrently from a number of sources equal to the number of channels in said matrix;

References Cited UNITED STATES PATENTS 2,417,450 3/1947 Sea-rs 3158.5 2,498,081 2/1950 Joel et a1 3158.5 2,517,712 8/1950 Riggen 315-8.5 2,534,372 12/1950 Ring 3158.5 2,616,060 10/1952 Goodall 315-8.5 2,916,660 12/1959 Ketchledge 315-85 2,934,673 4/1960 MacGriif 3158.5 2,991,459 7/1961 Darois 340347 X 3,095,517 6/1963 Fyler 315-8.5

MAYNARD R. WILBUR, Primary Examiner.

G. EDWARDS, Assistant Examiner.

US. Cl. X.R.

313 94, 346; 31s-s.s