US2303184A - Rectifier system for carrier-signal receivers - Google Patents

Description

Patented Nov. 24, 1 942 FFICE RECTIFIER. SYSTEM FOR CARRIER-SIGNAL RECEIVERS Harold a. Wheeler, Great Neck, 'N. 1n, asslgnor to Hazeltinc Corporation,

ware

a corporation or Dela- Application June 15, 1940, Serial No. 340,647

7 9 Claims.

This invention relates to rectifier the type wherein periodic potentials are converted to unidirectional potentials, and to such systems of this general type which include arrangements for reducing the ripple voltage components which frequently appear in the developed unidirectional potential. While the' invention is of general application, it has parthe automatic amplification ticular utility in control system of television receivers in which synchronizing-signal components of a television signal are rectified to develop a unidirectional automatic amplification control bias. The invention, therefore, will be described in tion with a television receiver wherein the in 'vention is used to aid in attaining exceptionally fast-acting automatic amplification control.

Automatic amplification control is commonly accomplished in television receivers by peak rectification of the synchronizing components of a received signal and by the utilization of the rectified signal to control the amplification of the signal-translating channel of the receiver inversely in accordance with the strength of the received signal. In those receivers adapted to receive a carrier wave negatively-modulated with videorequency components and line-synwave form now in use, it is necessary that the peak-rectifier circuit have a time constant which is long with respect to the period of the field-synchronizing components in order to provide a relatively steady automatic amplification control bias which, when used to control the amplification of the signal-translating channel of the receiver, does not produce undesirable shading effects in the reproduced picture or undesirable irregularities at the field-scanning frequency in the operation of the automatic amplification control system. It is, therefore, customary to provide in such tion, control systems time constants of the order of many times the period of the relatively lowfrequency field-synchronizing components and this period, for the standard television signal now in use, is of a second so that a time constant of the order of one second is commonly used. Television receivers matic amplification control systems having such time constants have the characteristic that the automatic amplificaprovided with autoy systems of particularly automatic amplification controlsystem responds slowly to changes in the at amplitude of the received signal.

While, in general, automatic amplification control systems having long time constants of this nature operate satisfactorily in those installations which are relatively free from disturbing noise, their operation is greatly impaired in those installations subject to high noise levels. Received noise eifectively increases the amplitude of the received signal to a value which may be several times its normal unmodulated value, and is thus effective to reduce the amplification of the receiver to a relatively small value, the amplification being restored to normal only after an appreciable period or time dependent upon the time constant of the peak-rectifier circuit. Repeated noise components separated by a time less than the time constant of the. peak-rectifier circuit may thus eflectively completely paralyze the receiver by the action of the automatic amplification control system, while sporadic noise components may cause either a complete or partial paralysis for an objectionable period of time.

It is an object of the invention, therefore, to provide a television signal receiver comprising an improved automatic famplification control rectifier system which avoids one or more of the above-mentioned disadvantages of such receivers of the prior art.

It is a further'object of the invention to provide a television signal receiver comprising an automatic amplification control rectifier system which possesses extreme sensitivity and great rapidity of control action and which; therefore; materially reducesthe 'eifect of noise disturbances on the operation of the receiver.

' ceiver but, in addition,

It is an additionalobject of the invention to provide a television signal receiver having an automatic amplification control rectifiersystem which not only responds rapidly to control the amplification of the signal channel of the rehas little or no tendency during operation. to produce shading eflects or other irregularities in the reproduced image due to the presence o1; field-synchronizing or 1ine-' synchronizing components.

In accordance with a feature of the invention,

a rectifier system in a carrier-signalv receiver comprises an input circuit adapted tohave applied thereto periodic potentials to be rectified, an output circuit having circuit elements including a pair of energy-storage devices, and a pair of rectifying means individually coupling the input circuit to the devices to develop two pulsating unidirectional potentials. The devices and the circuit elements associated therewith are so proportioned that the ratio of the amplitudes of the unidirectional potentials is independent of amplitude variations of the periodic potentials and the unidirectional potentials are unequalin the output circuit while the undesired pulsation components of the unidirectional potentials are of the same order of magnitude in the output circuit. Means are included in the output circuit for combining the unidirectional potentials with opposite polarities to derive a difl'erential unidirectional potential substantially free of the undesired potential pulsation components.

Alsoin accordance with a feature of the invention, a television receiver adapted to receive a television signal having video-signal components and periodic synchronizing-signal components has included therein an automatic control rectifier system comprising an output circuit including. a pair of time-constant circuits, and means responsive to the amplitude of the synchronizing-signa.l components for developing in '-each of the timewonstant circuits a pulsating unidirectional potential. The circuit element of the output circuit and the amplitude-responsive means are soproportioned that the ratio of the amplitudes of the developed potentials is indel pendent of amplitude variations of the periodic components and the unidirectional potentials vary unequally and proportionally with the amplitude of the received signal and independently of it vision-signal components while .the undesiredpotential pulsation'components of the developed unidirectional potentials are of the same order of magnitude. means for combining the developed unidirection- .al potentials with opposite polarities to derive a together with other and further objects thereof,

reference is had to the following description taken in connection with the. accompanying drawing and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a circuit diagram, partly schematic, of a complete television receiving apparatus embodying the invention; and Fig. 2 is a graph illustrating the wave forms of periodic voltage waves developed at different points in the system of Fig. l and isused as an aid in explaining the operation of the invention.

Referring now more particularly to Fig. 1 of the drawing, there is represented schematically a complete television signal receiver of a conventional design embodying the present invention in a preferred form. In general, the re- The output circuit includesceiver includes a tunable radio-frequency amplifier in having its input circuit connected to an antenna system II, 12, and having it output circuit connected to a tunable oscillator-modulator l3. Connected in cascade with the oscillator-modulator l3, in the order named, are an intermediate-frequency amplifier I4 of one or more stages, a detector IS, a video-frequency amplifier l6, and an image-reproducing device l1, preferably of the cathode-ray tube type. A linescanning'generator l8 and a field-scanning generator l9 are also coupled to the output of detector I5 by way of suitable synchronizing-signal separating apparatus 20, the output of the scanning generators I8 and I9 being coupled to the respective line-scanning and field-scannin elements of the image-reproducing device i1. Connected also to the output of the oscillator-modulator I3 is a sound-signal translating apparatus 2| which may include, in the order named, a sound-signal intermediate-frequency amplifier, a' detector, an audio-frequency amplifier, and a sound reproducer 22.

The stages or units Ill -22, inclusive, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are unnecessary herein. Referring briefly, however, to the operation of the system described above, television signals and their accompanying sound signals are intercepted by the antenna system ll, [2 and are selected and amplified in radio-frequency amplifier Ill and applied to the oscillator-modulator l3, wherein they are converted to intermediate-frequency vision signals and intermediate-frequency sound signals.

Th intermediate-frequency sound signals are applied to the sound-signal translating apparatus 2|, wherein they are amplified, detected, amplified at audio frequency, and applied to the sound-reproducing device 22 for reproduction.

The intermediate-frequency vision signals are applied to the intermediate-frequency amplifier ll for further amplification and are thereaiflter applied to the detector I 5 to derive the videofrequency modulation components of the vision signal. The modulation components are amplified by the video-frequency amplifier l6 and are applied in th usual manner to a brightness-control electrode of the image-reproducing device II. The intensity of the electron beam of tube I1 is thus modulated or controlled in accordance with the video-frequency voltages impressed on its control electrode in the usual manner.

The modulation components of the vision signal are also applied to the synchronizing-signal separating apparatus 20 wherein the synchronizing components are separated from the vision-signal components and the line-synchronizing components and field sy'nchronizing components are separated from each other and applied, respectively, to the line-scanning generator 18 and fieldscanning generator l9. Saw-tooth current or voltage scanning waves are generated in the linescanning and field-scanning generators l8 and II, respectively, in synchronism with the synchronizing components applied to the generators and the scanning waves so generated are applied to the scanning elements of the cathode-ray tube H to produce electric scanning fields, thereby to deflect the electron beam of the tube in two directions normal to each other so as to trace a rectilinear scanning pattern on the screen of the tube to reconstruct the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1 embodying the present invention, for the purpose of developing a controlbias voltage proportional to the amplitude of the received television signal and independent. of its vision-signal components, there is provided an automatic amplification control rectifier system 23 preferably coupled to that output circuit of the synchronizing-signal separating apparatus 20 to which the line-scanning generator I 8 is connected to derive only line-synchronizing components therefrom; The automatic amplification control system 23 comprises an input circuit adapted to have applied thereto periodic potentials to be rectified. The input circuit includes a transformer 24 having a primary winding 25 connected, as previously stated, to the output of the synchronizing-signal separating apparatus 20, and having a secondary winding 26 across the terminals of ,which is connected a first rectifier system. This system comprises a diode rectifier 21 and an energy-storage device which may be a condenser 29. A resistor 28 is connected in parallel with the condenser 29 to provide a discharge path for the latter. A portion a-b of the transformer secondary winding 28 also constitutes the coupling to a second rectifier system comprising a diode rectifier 30, a resistor 3|, and an energystorage device comprising a condenser 32. The condensers 29 and 32 and their respective parallel connected resistors 28 and 3| form two time- constant load circuits 28, 29 and 3|, 32 one for each of the described rectifying systems. The load circuits are effectively connected in series opposition, one terminal being grounded and the other being connected to the A. V. C. circuit of the receiver through a filter network 33, comprising series- resistor arms 34, 35 and an interposed to vary the amplification of shunt condenser arm 36. The automatic ampllfication control or A. V. C. circuit is connected to the control grids of one or more of the tubes of the oscillator-modulator [3, the radio-frequency amplifier I 0, and the intermediate-frequency amplifier M. The time constants of the time- constant circuits 28, 29, 3|, 32, and the filter network 33 are preferably of the order of several periods of the line-synchronizing components, for example, five to twenty line periods.

In considering the operationof the portion of the transformer secondary winding 26 are rectified by the diode rectifier 30 to develop in the time-constant circuit 3|, 32 a pulsating unidirectional potential represented by the curve f 01' Fig. 2, this potential with respect to ground. If either of the developed potentials e or f of Fig. 2 were alone applied through the filter network 33 to the. automatic amplification control or A. V. C. circuit of the receiver to control the amplification thereof, the pulsations of saw-tooth wave form occurring in these potentials would so change the instantaneous amplification that undesirable shading effects would occur in the reproduced image, thereby impairing the quality of the image. However, by combining these potentials with opposing polarity, the pulsations occurring in one of the unidirectional potentials opposes the pulsations occurring in the other and the differential unidirectional potential developed between the point 0 and ground is relatively free of undula tions, if thetime-constant circuits are properly proportioned in a manner presently to be considered, and' varies in magnitude with the strength of the received signal and independently of its vision-signal components. This differential potential is applied through the filter network 33 the units l8, |3,and l4 inversely in accordance with the amplitude of the received signal and independently of its vision-signal components.

The time constants of the time- constant circuits 28, 29, 3|, 32, and of the filter network 33 are less than the field-scanning period, being of the order of several line-scanning periods, so

that the effect of received noise disturbances is at most only to reduce the amplification of the receiver during the occurrence of the noise disturbthe television system constituting thepresent inv vention, it will be assumed that there is being received a television signal of the standard wave form nowin general use, that is, a carrier wave negatively-modulated with vision-signal components and periodic line-synchronizing and fieldsynchronizing components of the amplitude range outside the amplitude range of the vision-signal components. The demodulation components of the received television signal are derived in the,

detector I5 and are applied to the synchronizingsignal separating apparatus 20. Here, the periodic synchronizing-signal components are separated from the vision-signal components and the line-synchronizing components thereof are separated from the field-synchronizing components and are applied to the transformer 24 as periodic pulses having the wave form, illustrated by the curve d of Fig. 2.

These periodic pulses appear in the secondary winding 28 of the transformer and are rectified by the diode rectifier 21 to develop across the time-constant circuit 28, 29 a pulsating unidirectional potential represented by the curve e of Fig. 2, which is shown as having a negative polarity with respect to ground. Similarly, the potential pulses appearing in the portion (1-!) of ances and for a relatively short interval, for example, ten line-scanning periods, after the noise disturbances have passed.

The proper proportioning of the time- constant circuits 28, 29 and 3|, 32 with relation to each other and to the potentials applied to the diode rectiflers 21 and 30 is important. Since the periodic line-synchronizing components have the rectangular wave form represented by the curve d of Fig. 2, and since the time constants of the time- constant circuits 28, 29 and 3|, 32 are several line-scanning periods, the pulsations occurring in the unidirectional potentials developed in the time- constant circuits 28, 29 and 3|, 32 have a saw-tooth Wave form as represented by the curves tion of portions g with interposed relatively longer exponential portions h. Similarly, the saw-tooth pulsations of curve f have relatively short exponential portions 1' longer exponential portions in. If the slopes of the exponential portions merically equal but of opposite senses to the respective slopes of the exponential portions 2' an'd'k of curve I, the pulsations exactly oppose when the developed potentials of the time-constant cir-.

cuits 28, 29 and 3| 32 are combined with opposing polarities, the unidirectional differential potential appearing between point e and ground being, therefore, substantiallyfree of any pulsation.

having a positive polarity e and f of Fig. 2. Each saw-tooth pulsathe curve e has relatively short exponential with interposed relatively g and h of curve e are nu- E=the amplitude of the applied periodic potential;

C:the capacitance of the time constant circuit;

and

R=the resistance of the time-constant circuit,

and the subscripts I'and 2 refer to the time- constant circuits 28, 29 and 3|, 32, respectively.

It is evident from Equation 1 that the time constants of the rectifier circuit elements should bear the same ratio to each other as the ratio of the voltages applied to their respective rectifiers in order that the ripple voltage components of the rectified voltages shall be equal. In this connection, it may be pointed out that this type of ripple compensation is approximately independent of the frequencies of the ripple voltage components of the rectified voltages, this fact making it possible to compensate ripple voltages of sawtooth .wave form which have a large number of frequency components.

In practice, the transformer secondary winding 26 may be center tapped so that the periodic voltage applied to the diode rectifier 21 is twice that applied to the diode rectifier 30. In this event, either the two condensers 29 and 32 may be equal or the two resistors 28 and 3| may be equal, as desired; in either case the time constant of the resistor 28 and condenser 29 being twice the time constant of the resistor 3| and condenser 32.

It will be apparent from the description above that the input circuit of the control system comprises means for applying the line synchronizingsignal-components to the rectifying systems wherein they are peak-rectified. The rectifiers 27, 30 and the input circuit thus comprise means responsive to the amplitude of the synchronizingsignal components for developing a pulsating unidirectional potential in each of the time- constant load circuits 28, 29 and 3|, 32. The time-constant circuits are connected in series opposition to form means included in the output circuit of the automatic control rectifier system for combining the .developed unidirectional potentials. The circuit elements of the output circuit and the amplitude-responsive means are so proportioned that the ratio of the amplitudes of the developed unidirectional potentials is independent of amplitude variations of the periodic synchronizingsignal components and the unidirectional poten-.

tials vary unequally and proportionally with the amplitude of the received signal but independently of its vision-signal components. Their proportioning is also suchthat the undesired potential pulsation components of the unidirectional potentials are of the same order of magnitude in the output circuit, whereby the derived differential unidirectional potential is substantially free of undesired potential pulsation components.

From the foregoing description of the invention and its operation, it will be evident that the important considerations are that the unidirectional potentials developed across th resistors 28 and 3| shall be unequal and that the time constants of the rectifier systems shall bear a predetermined relation to each other and to the amplitudes of the applied periodic potentials. When the circuit elements of the output circuit and the rectifying systems are proportioned in the manner outlined, the ratio of the amplitudes of the unidirectional potentials developed across the resistors 28 and 3| are independent of amplitude variations of the applied periodic potentials.

Further, the unidirectional potentials vary unequally and proportionally with the amplitude of the television signal and independently of its vision-signal components, while the undesired periodic potential pulsations of the developed unidirectional potentials are of the same order of magnitude. The differential unidirectional potential is thus free of any undesirable pulsations of line-scanning or field-scanning frequency.

1. In a carrier-signal receiver, a rectifier system comprising, an input circuit adapted to have applied thereto periodic potentials to be rectified, an output circuit havingcircuit elements including a pair of energy-storage devices, and a pair of rectifying means individually coupling said input circuit to said devices to develop two pulsating unidirectional potentials, said devices and the circuit elements associated therewith being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent of amplitude variations of said periodic potentials and saidunidirectional potentials are unequal in said output circuit while the undesired pulsation components of said unidirectional potentials are of the same order of magnitude in said output circuit, said output circuit including means for combining said unidirectional potentials with opposite polarities to derive a differential unidirectional potential substantially free of said undesired potential pulsation components.

2. In a television receiver adapted to receive a television signal including vision-signal components and periodic synchronizing-signal components, an automatic control rectifier system comprising, an output circuit including a pair of time-constant circuits, and means responsive to the amplitude of said synchronizing-signal components for developing in each of said time constant circuits a pulsating unidirectional potential, the circuit elements of said output circuit and said means being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent of amplitude variations of said periodic components and said potentials vary unequally and proportionally with the amplitude of said received signal and independently of its vision-signal components while the undesired potential pulsation components of said unidirectional potentials are of the same order of magnitude, said output circuit including means for combining said unidirectional potentials with opposite polarities to derive a differential unidirectional potential substantially free of said undesired potential pulsation components.

3. In a television receiver adapted to receive a r 8,808,! "television signal including vision-signal comtude variations of said periodic components and magnitude, and an output circuit including means for combining said unidirectional potentials with opposite polarities to derive a differential unidirectional potential substantially free of said A;

undesired potential pulsation components.

6. In a television receiver adapted to receive a television signal including vlsion-signalcomponents and periodic synchronizing-signal components, an automatic control rectifier system comprising, an output circuit including a pair of time-constant circuits each having a time constant equal toseveral periods of'said synchrosaid potentials vary unequally and proportionally 1 with the amplitude of said received signal and independently of its video-signal components while the undesired potential pulsation components of said unidirectional potentials are of the same nizing-signal components, and means responsive to the amplitude ofsaid synchronizing-signal order of magnitude, said output circuit including means for combining said unidirectional potentials with opposite polarities to derive a differential unidirectional potential substantially free of said undesired potential pulsation components.

4. In a television receiver adapted to receive a television signal including vision-signal components and periodic synchronizing-signal components, an automatic control rectifier system comprising, a pair of rectifying systems each having a time-constant load circuit, means for said time-constant load circuits a pulsating u'mdirectional potential, the circuit elements of said rectifying systems and said means being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent of amplitude variations of said periodic components and said potentials vary unequally and proportionally with the amplitude of said received signal and independently of its vision-signal components while the undesired potential pulsation components of said unidirectional potentials are of the same order of magnitude, and an output circuit including means for connecting said load circuits in series with opposite polarity so that said potential pulsation components are of opposite phase, whereby said unidirectional potentials arecombined to derive in said output circuit a diiierential unidirectional potential substantially free ,of said undesired potential pulsation components.

5. In a television receiver adapted to receive a I television signal including vision-signal components and periodic synchronizing-signal components, an automatic control rectifier system comprising, a pair of rectifying systems each having a time-constant load circuit, thetime constant of one of said load circuits beinggreater than that of the other, means for applying said synchronizing-signal components to said rectifying systems to develop in each of said time-constant load circuits a pulsating unidirectional potential, the magnitude of the synchronizingsignal components applied tothe one of said rectifying systems having said one load circuit being larger than that applied to the other and the circuit elements of said time-constant load circuits and said means being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent of amplitude variations of said periodic components and said potentials vary unequally and proportionally with the amol its vision-signal components while the undesired potential pulsation components of said uniof its vision-signal components .while the unidirectional potentials are 'of the same order applying said synchronizing-signal components to said rectifying systemsvto develop .in each of components for developing in each of said timeconstant circuits a pulsating unidirectional potential, the circuit elements of said output circuitand said means being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent of amplitude variations of said periodic components and said potentials vary unequally and proportionallywith the amplitude of said received signal and independently undesired potential pulsation components of said of magnitude, said output circuit including means for combining said unidirectional potentials with opposite polarities to derive a diil'erential unidirectional potential substantially free of said a undesired potential pulsation components.

7. In a television receiver adapted to receive a television signal including vision-signal components and periodic synchronizing-signal coi'nponents consisting of line-frequency and fieldfrequency synchronizing pulses, an automatic control rectifier system comprising, an output circuit including a pair of time-constant circuits each having ra time constant greater than the line-frequency periods but less than the fieldi'requency periods of said synchronizing-signal components, and means responsive to the amplitude of said synchronizing-signal components fordeveloping in each of said time-constant circuits a pulsating unidirectional potential, the circuit elements of said output circuit and said means being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent 'of amplitude variations of said periodic compo-' nents and said potentials vary unequally and proportionally with the amplitude of said received signal and independently of its vision-signal oomponents while the undesired potential pulsation components of said unidirectional potentials are of the same order of magnitude, said output cir-- cuit including means for combining said unidirectional potentials with opposite polarities to derive a differential unidirectional potential substantially free of said undesired potential pulsation components. a

8. In a television receiver adapted to receive a television signal including vision-signal components and periodic line-synchronizing-signal components. an automatic control rectifier system comprising, an output circuit including a pair of time-constant circuits, and means for peakrectifying said line-synchronizing-signal components to develop in each of said time-constant plitude of said received signal and independently circuits a pulsating unidirectional potential, the circuit elements of said output circuit and said means being so proportioned that the ratio of the amplitudes of said unidirectional potentials is independent of amplitude variations of said directional potentials are of the same order of {I periodic components and said potentials vary unequally and proportionally with the amplitude of said received signal and independently of its vision-signal components while the undesired potential pulsation components of said unidirectional potentials are of the same order of magnitude, said output circuit including means for combining said unidirectional potentials with oppositepolarities to derive a diflerential unidirectional potential substantially free of said undesiredpotential pulsation components.

9. In a television receiver adapted to receive a television signal including vision-signal components and periodic synchronizing-signal components, an automatic control rectifier system comprising, a pair of time-constant circuits, one

of which comprises resistance R1 and capacitance C1 and the other of which comprises resistance R2 and capacitance C2, means responsive to a potential E1 proportional to the amplitude of said synchronizing-signal com nts for developing in said one time-constant circuit a pulsating unidirectional potential, means responsive to a potential E2 proportional to the amplitude of said synchronizing-signal components for developing in said other of said time-constant circuits a pulsating unidirectional potential, the ratio of the amplitudes of said potentials E1 and E2 being independent of amplitude variations of said components and the circuit elements of said timeconstant circuits being proportioned in accordance with the expression and an output circuit including means for combining said unidirectional potentials with opposite polarities to derive a difierential unidirectional potential substantially free of said potential pulsation components.

HAROLD A. WHEELER.

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