US2295816A - Signal-translating stage - Google Patents

Description

Sept. 15, 1942. J. c; WlLSON SIGNAL-TRANSLATING STAGE Filed Sept. 9, 1940 2 Sheets-Sheet l o. .m R wm am m J E... u WP M A m 4 5 f m R N m 0 T T .l A o m w 0 L P m x F O a B R -c m m P VE m 2.. F

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INVENTOR 0. WILSON OHN ATTORNEY Sept. 15, 1942.

FIG. 3.

J. C. WILSON SIGNAL-TRANSLATING STAGE F IG.4

FIG. 5.

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INVENTOR OHN 0. WILSON BY ATTORNEY Patented Sept. 15, 1942 SIGNAL-TRANSLATIN G STAGE John 0. Wilson, Bayaide, n.1,

aasignor to Hazeltine Corporation, a corporation oi Delaware Application September 9, 1940, Serial No. 355,942 9 Claims. (01. 179-171) This invention relates generally to a signaltranslating stage adapted to translate a signal input having a wide amplitude range and particularly to such a signal-translating stage in which the direct current component in the output circuit thereof does not vary appreciably as the gain of the stage is adjusted over a relatively wide range.

In some modulated-carrier signal-translating systems, the amplitude of the signal input to a signal-translating stage varies within very wide limits. This is true of the first signal-translating stage of a modulated-carrier wave-signal receiver under normal operating conditions. For weak signals it is desirable to maintain the transmission characteristic, or the response, of the preselector between the antenna and the first repeater stage of the receiver at a maximum in order to raise the received signal substantially above the noise level, thus to procure maximum useful sensitivity of the receiver. However, with a high gain in the preselector, as 'the strength of the desired received signal increases to such an extent that the grid swing ofthe first repeater stage includes a substantial nonlinear portion of the characteristic curve of the repeater, distortion of the desired signal-modulation envelope and cross modulation of the desired signal-carrier wave by strong undesired signals may result. This is particularly true in the case of receivers provided with automatic amplification control by which strong signals cause the grid of the first repeater stage to be biased toward that portion of its characteristic which is most nonlinear. signals, as well as desired signals, which reach the grid of the first repeater stage of the receiver have the effect of causing the grid to swing over such an amplitude range that these disturbing efl'ects result. It is well known that such envelope distortion and cross modulation are effects which cannot be filtered out by succeeding selector circuits of the receiver.

In general, the preselector of a receiver should be selective to pass a band of desired modulation frequencies sufilciently wide to provide the desired fidelity of reproduction. Generally speak n if an attempt is made to decrease the total desired and undesired signal input of the first repeater stage by discriminating against the undesired signals passed by the selector by adjusting its -band width, the fidelity of reproduction is impaired to an undesirable degree. Further, this does not remove the envelope distortion of abnormally strong desired signals.

Various expedients have heretofore been protenuating the input to the first repeater stage of a modulated-carrier signal receiver in order to eliminate the disturbing effects described above. In certain of these arrangements, adjustable impedanceelements, such as vacuum tubes, have While such arrangements provide generally satis- Undesired factory operation, they have usually required the use of one or more additional vacuum tubes, or other circuit complexities which tend to increase the cost of the receiver.

Another arrangement which has been utilized for the purpose is that described and claimed in the copending application of Arthur V. Loughren, Serial No. 335,238, filed May 15, 1940,

' now Patent No. 2,263,825, November 25, 1941, and

assigned to the same assignee as. the present application. While the arrangement of the said copending application is generally satisfactory, one characteristic of the system which is undesirable in certain applications is that the direct current component in the output circuit of the stage varies as the gain of the stage is varied.

- This characteristic is also found in the other prior posed for automatically and adjustably tart arrangements mentioned above.

In certain applications it is disadvantageous to utilize an adjustable-gain signal-translating stage the unidirectional component of the output current of which varies with the gain-of the stage. Thus, in a television video-frequency amplifier it is necessary to translate signal components of very low frequencies. If such a signal-translating stage having an adjustable gain is utilized in a television transmitter, any gain adjustment which is effected upon the stage usually has the eilfect of temporarily interrupting or adding spurious transients to the picture transmission for an appreciable interval, due to the time constants of the circuits utilized in the coupling system of the video-frequency amplifier. Such interruptions and spurious transients are highly undesirable and it is, therefore, desirable to provide a signaltranslating stage the gain of which may be adjusted within wide limits and the unidirectional component of the output current of which is not subject to an appreciable variation with the ain adjustment.

Also in preattenuator circuits of the types described above, the direct current component of the adjustable-gain stage used in such stages varies widely with an adjustment of gain oi? the signal-translating stage, as described above. This is particularly true of adjustable-gain signal-translating stages utilizing a variable-mu tube of conventional type. The range of variation of the direct current component of such stages may be more than :1 and such a wide range of variation may tend to affect appreciably the voltage regulation of the supply source. It is, therefore, highlydesirable to provide an adjustable-gain signal-translating stage the gain of which may be varied over wide limits and the output current of which is substantially constant under any conditions of gain control.

It is an object of the present invention, therefore, to provide an improved signabtranslating stage which is not subject to one or more of the above-mentioned disadvantages of prior art arrangements.

It is a further object of the invention to provide an improved signal-translating stage the gain of which is adjustable over a wide range of values- It is still another object of the invention to provide a signal-translating stage the gain of' which is adjustable over a. wide range of values and the direct current output of which does not vary appreciably with adjustments of the gain of the signal-translating stage.

In accordance with the invention, a signaltranslating stage comprises a pair of signal-input terminals and a vacuum tube, including means for forming an electron beam the crosssection of which is limited in at least one dimension, and a control grid intersecting the electron beam and wide relative to the width of the beam in the limited dimension. The stage further includes means for coupling the control grid between the input terminals efiectively to comprise a voltage divider across its width and means for deflecting the electron beam in the direction of its limited dimension to control the gain of the stage by the action of the control grid.

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

In the accompanying drawings, Fig. 1 is a schematic circuit diagram of a complete television transmitting system including a signaltranslating stage in accordance with the invention; Figs. 2, 3, 4, and 5 illustrate details of the tube of the signal-translating stage of Fig. 1 incorporating the invention; while Fig. 6 is a circuit diagram, partly schematic, of a complete television receiving system embodying a signaltranslating stage in accordance with the invention as the first stage in the signal-translating channel of the receiver.

Referring now more particularly to Fig. 1 of the drawings, there is shown a schematic circuit diagram of a, television transmitting system comprising a video-frequency signal generator ll, which may include the usual cathoderay signal-generating tube and scanning and wave-shaping apparatus. Connected in cascade to the output circuit of the signal generator I3,

in the order named, are a first video-frequency amplifier II, a second video-frequency amplifier l2, a third video-frequency amplifier IS, a modulator I4 and an associated carrier-frequency oscillator l5, a power amplifier l8, and a radiating antenna system l1, Is. For the purpose of developing and transmitting a composite synchronizing signal and for synchronizing the scanning of the video-frequency generator Ill therewith, there is provided apparatus including a line-frequency generator 20 and a field-frequency generator 2| having their output circuits coupled to a mixing amplifier 22, the output circuit of which is, in turn, coupled to the videofrequency amplifier |3. Output circuits of linefrequency generator 20 and field-frequency generator 2| are also coupled to the video-frequency signal generator I0. timing-impulse generator 23 for the purpose of controlling the operation of line-frequency generator 20 and field-frequency generator 2|. The generator 23 is preferably stabilized by means of a connection 24 to a suitable source of periodic voltage, for example, to the power-supply circuit or to the synchronizing-voltage source of motion picture mechanism, where such is employed.

Neglecting for the moment the details of operation of the signal-translating stage l2, the system just described comprises the elements of a television transmitting system of conventional design and, since the various parts thereof with the exception of stage l2 may be of any wellknown construction, a detailed description of the general system and its operation is unnecessary. Briefly, the image of the scene to be transmitted is focused on the target in the signal generator l0 and a video-frequency voltage is developed thereby in the usual manner and is applied to the video-frequency amplifier wherein this voltage is amplified and from which it is transmitted through amplifier I2 to the video-frequency amplifier l3. The composite synchronizing signal developed by the mixing amplifier 22, as will presently be described in more detail, is also applied to the video-frequency amplifier L3 in which it is mixed with the video-frequency signal and further amplified. The amplified composite signal is supplied to the modulator I wherein it is so impressed upon the carrier wave generated by the oscillator [5 as to develop a modulated-carrier signal. This signal is delivered to the power amplifier l6 for amplification therein and is thereafter impressed upon the antenna system ll, l8 to be radiated.

Timing pulses developed by the generator 23 are applied to the generators 20 and 2| to lock the same in synchronism. An output voltage of each of the generators 20 and 2| is applied to the mixing amplifier 22 in order to generate the required composite synchronizing signal for transmission. Output voltages of generators 20 and 2| are also supplied to the video-frequency signal generator l0 to synchronize the operation thereof.

Referring now more particularly to the ap- There is also provided a and ii. The tube structure is illustrated in more detail in the partially sectionalized perspective drawing of Fig. 2. The tube is provided with control grids It and 31 which intersect the beams II and II, respectively, the control grids being wide relative to the widths of the beams in the above-mentioned limited dimension. Conductor II and conductor II are effective individually to couple the grids I! and 31 between the input terminals 3|, 8|, effectively to cause the grids to comprise voltage dividers across the width of the grids. Focusing plates ll, 42, maintained near the potential of the cathode 43 of the tube, are provided for generating the beams 34 and II which are limited to a ribbon shape, as described above. The tube is also provided with an anode It, the cathode l3 and the anode It effectively comprising concentric cylinders surrounded by the envelope of the tube. In order to deflect the electron beams 34 and 35 in the direction of the limited dimensions of the beam, that is, circumferentialiy within the tube 32, to control the gain of the stage II; there is provided a suitable beam-deflecting means, such as a winding ll. surrounding the tube 32 andadapted to be excited by direct current from a source it through a voltage divider ll having an adjustable tap ii. The voltage divider BI and the adjustable tap ll therefore are included in a means for adjusting the amount of deflection of the electron beams 34 and 35 to adjust the gain of the stage to any desired value within relatively wide limits by the action of the control grids 38 and 31. The use of such a magnetic beam-deflecting means rather than an electrostatic deflecting means facilitates the desired deflection without affecting the mean anode current of the tube. A cathode-biasing resistor 52 is provided for tube 32, by-passed for currents of signal condenser I8.

Reference is made to Figs. 3, 4, and 5 for a more detailed description of the construction of the grids of the tube of the signal-translating stage it. Each of the grids ll and if! is constructed effectively to comprise a voltage divider coupled between terminals 30, II, as indicated schematically in Fig. 3. where the vertical members 54 represent the wires of the grid which are parallel to the cathode 43 of the tube. The grid is so constructed as effectively to provide resistors 5! coupling adjacent ends of conductors 54, as illustrated in Fig. 3. The control grid therefore effectively comprises across its width electron-controlling conductors effectively spaced by resistors. The grid may be construct ed, for instance, as illustrated in Fig. 4, where mica discs 5., it are utilized to support the grid wires 54. A conductive material, for instance, some sputtered resistive coating on discs 56, is utilized effectively to form the resistors 55 of Fig. 3. A morev complete detail of this construction is illustrated in Fig. 5, wherein the resistive coating is designated by the reference numeral I.

In considering the operation of the signaltranslating stage I! of Fig. 1, it will be seen that, due to the voltage-dividing properties of grids 3t, 31, substantially the entire signal voltage is available for utilization to control the intensity of beams 34 and 35 when deflected to the position shown. since the beams intersect the grids near their high signal-potential terminals. Thus, under this condition of operation, the siglating stage II effectively has a relafrequency by means of a tively high gain. However, if the tap Ii on voltage divider II is adjusted .to change the current in winding 48, thereby to deflect the beams 34 and I in a counterclockwise direction, the beams then intersect portions of the voltage-dividing grids which are at an appreciablylower signal potential. Therefore, under these conditions, the gain of the stage is materially reduced. However. it will be noted that the unidirectional bias provided for the grids 3t and I! by the cathode resistor 82 is not changed by this adjustment and, inasmuch as the control grids It and 31 are homogeneous, that is, they have the same spacing for all equivalent circumferential. portions, the direct space current of the tube does not vary with the gain adjustment. The cathode resistor 52 therefore is included in the means for uniformly biasing the control grid. 3

Therefore, it is seen that the signal-translating stage I: is one adapted to have its gain adjusted over a wide range and in which the direct current component in the signal-output circuit of the stage does not vary appreciably with the gain adjustment, thus providing the advantages mentioned in the preliminary portion of the specification.

Referring now more particularly to Fig. 6 of the drawings, there is illustrated a superheterodyne receiver including a signal-translating stage in accordance with the invention as the first stage in the signal-translating channel of the receiver. This receiver comprises, coupled in cascade with an antenna-ground circuit I, H, a radio-frequency amplifier l2 coupled to antenna circuit 6|, I through a selective circuit I1, 63, it, a frequency changer or oscillator-modulator I, an intermediate-frequency amplifier it of one or more stages, a detector and A. V. 0. supply 61, an audio-frequency amplifier ll of one or more stages, and a sound reproducer es. Automatic amplification control is secured in a well-known manner by applying a unidirectional voltage derived from A. V. C. supply 61 to the control electrodes of one or more of the tubes included in the oscillator-modulator i5 and intermediate-frequency amplifier it.

A novel type of automatic amplification control is also provided within the signal-translating stage II, the constructional details of which are generally similar to those of stage I! of Fig. 1 and circuit elements which are similar in the two figures have identical reference numerals. The signal-translating stage I! differs from that of stage I! of Fig. 1 primarily in the means provided for supplying direct current to the winding 48 to. control the gain of the stage. In the circuit of Fig. 6 the voltage provided by the A. V. C. supply 61 is amplified in an A. V. C. amplifier H, the output of which is utilized to provide the direct current for winding 48. The general operation of the superheterodyne receiver of this figure is entirely conventional and need not be described in detail.

It is believed that the operation of the signaltranslating stage I! of Fig. 6 will be readily apparent from the description which has been given above of the operation of the signal-translating stage it, the only difference in the operation being that the gain control is effected in the circuit of Fig. 6 by the direct current supplied by amplifier ll rather than by the direct current supplied by the battery 4!. Therefore, the gain of signaltranslating stage I 2' may be varied within very wide limits with substantially no effect upon the source of supply or the, unidirectional operating voltages provided for the tubes of the receiver.

and modifications as fall within the true spirit,

and scope of the invention.

What is claimed is: r g

1. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a control grid intersecting said-- beam and wide relative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals effectively to comprise a voltage divider across its width, and means for deflecting said electron beam in the direction 01 its limited dimension to control the gain of said stage by the action of said control grid.

2. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a homogeneou control grid intersecting said beam and widerelative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals eflectively to comprise a voltage divider across its width, and means for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action of said control grid.

3. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a control grid intersecting said beam and wide relative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals effectively to comprise a voltage divider across its width, means for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action of said control grid, and means for uniformly biasing said control grid.

4. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a homogeneous control grid intersecting said beam and wide relative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals effectively to comprise a voltage divider across its width, means for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action of said control grid, and means for uniiormly biasing said control grid.

5. A signal-translating stage comprising, :a pair the operation of of signal-input-terminals, a vacuum tube including means for forming an electron beam of ribbon shape in said tube whereby the cross-section is limited in one dimension and a control grid been described what are at intersecting said beam and wide relative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals eflectively to comprise a voltage divider across its width, and means for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action of said control grid.

6. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for formin cross-sectionoi which limited in at least one dimension and a control grid intersecting said beam which is wide relative to the width oi said beam in its limited dimension and which eilectively comprises across its width electron-controlling conductors effectively spaced by resistors, means for coupling said grid between said input-terminals efiectively to comprise a voltage divider across its width, and means for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action of said control grid.

7. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a control grid intersecting said beam and wide relative to the width or said beam in said limited dimension, means for coupling said grid between said input terminals eil'ectively to comprise a voltage divider across its width, and magnetic means for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action or said control grid.

8. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a control grid intersecting said beam and wide relative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals eflectively to comprise a voltage divider across its width, and a winding surrounding said tube and adapted to be energized by a unidirectional current for deflecting said electron beam in the direction of its limited dimension to control the gain of said stage by the action of said control grid.

9. A signal-translating stage comprising, a pair of signal-input terminals, a vacuum tube including means for forming an electron beam the cross-section of which is limited in at least one dimension and a control grid intersecting said beam and wide relative to the width of said beam in said limited dimension, means for coupling said grid between said input terminals eflectively to comprise a voltage divider across its width, means for deflecting said electron beam in the direction of its limited dimension, and means for adjusting the amount of deflection to adjust the gain of said stage by the action of said grid to any desired value within relatively wide limits.

JOHN C. WILSON.

an electron beam the,

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