US2482973A - Frequency multiplier - Google Patents

Description

Sept. 27, 1949.

I. J. F. GORDON 2,482,973

FREQUENCY MULTIPLIER Filed April so, 1946 OSCILLATOR ,-I2 v o v- II 35 PULSE A4 A8 EidT? 34 20 R- F /l 1 VIDEO R. F. OUTPUT I5 I AMPLIFIER 7 AMPLIFIER l 24 DELAY CIRCUIT Fig. 1

l0 OSCILLATOR 29 H PULSE II PULS I GROUPS FORMINEG V OUTPUT cIRcuI'r AMPLIFIER M V x22 Hg. 2 l5 DELAY CIRCUIT 40 BLOCKING I 42 CIRCUIT 38 Jorhe F. Gordon Patented Sept. 27, 1949 FREQUENCY MULTIPLIER James F. Gordon, Towson, Md., assignor to Bendix Aviation Corporation, Towson, Md., a corporation of Delaware Application April 30, 1946, Serial No. 665,957

9 Claims. (01. 250-36) This invention relates to frequency multipliers and more particularly to multipliers adapted to the multiplication of narrow pulses at a stable repetition rate.

This application has been divided and a divisional application bearing Serial No. 758,960 was filed July 3, 1947.

In previous practice the multiplication of frequencies has been subject to various limitations and defects. Some methods are limited to doubling so that a large number of stages are needed to provide any extended factor of multiplication. When power requirements must be met by an amplifier used selectively as amplifier, doubler, or tripler, then methods of regulation must be added to provide the proper output for the selected condition of operation. In cases where power is not a requirement, other higher harmonics of an oscillator or amplifier may be selected and amplified, but then only of a somewhat limited order. In any such situation where harmonic distortion, selection, and amplification are used, the problem of isolation of the desired harmonic from the many spurious oscillations and unwanted harmonics is not an easy one nor is it usually favorably accomplished.

An object of this invention is to provide a means of frequency multiplication in which the desired factor of multiplication may be readily obtained without recourse to a large number of multiplying channels.

Another object of this invention is to provide a means of frequency multiplication by which a large number of available frequencies are readily selectable from one stable oscillator source.

A further object of this invention is to provide a means of frequency multiplication in which unwanted harmonics and spurious oscillations are not present to be amplified by the succeeding stage or stages.

Another object of this invention is to provide a means of frequency multiplication in which selection of pre-set frequency is readily accomplished, both in calibration and operation, with a minimum of adjustment and control devices.

. Still another object of this invention is to provide a means of frequency multiplication with an output of short pulses at a definite repetition rate, and which means of multiplication effectively lends itself to further control to provide an output of regular, successive groups of two or more pulses.

Other objects and advantages of the invention will become apparent from a consideration of the following specification when taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a block diagram showing a multiplying circuit embodying the invention, in relation to its input, output, and tuning means; and,

Fig. 2 is a block diagram showing a modified form of the circuit of Fig. l in which the multiplier lends itself to the control of a blocking oscillator to provide an output of regular groups of pulses.

In Fig. l the output of an oscillator II] is connected by a lead I2 to a pulse forming circuit I4 which combination supplies the pulse input energy required by the invention. The output of the pulse forming circuit I4, is connected by a lead It to the input of a video amplifier 20. The output of the amplifier 21! is fed by a lead 22 to a delay circuit 24, and from said delay circuit by a lead 26 back to the input of amplifier 20. Connected into the anode circuit of the amplifier 20 by two leads I8 is a current meter 30. Representing one use of this invention, the output from amplifier 20 is fed by connector 32 to drive and control a radio frequency amplifier 34, which is preferably a tuned, class C amplifier. The output tank circuit d2 of the amplifier 34 comprises a coil 46 and a variable condenser 44, which may be ganged for tuning purposes with variable condensers 52 and 5a which control the delay applied by the delay circuit 24. The ganging means is indicated by the dashed line 5!).

In operation, the oscillator H), which is preferably crystal controlled for stability, provides the fundamental operating frequency. To provide the pulsed output needed for the present means of frequency multiplication, the fundamental oscillation frequency having a wave-form indicated by the graph i I is fed to the pulse forming circuit 14, the output of which consists of very narrow pulses as shown by graph l5, having a regular repetition rate established by the oscillator l0. These pulses are fed to the video amplifier 20 and subsequently multiplied in a manner now to be described.

If a very narrow pulse is fed to the video amplifier 2B, the amplified pulse will be fed to the delay circuit 24 and again to the input I3 of said amplifier, where the delayed pulse will again be amplified and will follow the initial pulse by an interval equal to the delay time of the delay circuit 24. The second pulse will again be fed to the delay circuit 20 and back to the input 18 of the amplifier 20 where it will be amplified and will follow the other two pulses by an interval 3 equal to the delay interval between the first two pulses. Such action is started by each pulse from the pulse forming circuit [4.

If the delay circuit 24 is set So that the delay time is 90 of the frequency cycle time of the output of oscillator Ill, then three pulses will follow the initial pulse through the video amplifier 58 before the arrival of the next pulse from the pulse forming circuit M. This pulse will occur in step and identify itself with the fourth fedback pulse which is 360 behind the initial pulse to pass the amplifier 2c. The output of amplifier. will now have a wave-form such as indicated by the graph 33.

Under these conditions it can be seen that the output of said video amplifier consists of four times as many pulses per second; as are present in the pulse source from the pulse forming circuit 14. If the delay circuit 25 were set for a relay of 120 of the fundamental frequency cycle, then the pulse frequency at the output of the video amplifier would be three times that of the initial frequency from the pulse formin circuit. If the delay \vere'set at 45, then the fre-- quency at the output of the'video amplifier would be eight times the initial frequency. Such multiplication could continue up to the limits of the pulse width and the capabilities of thedelay circuit 24.

With a current meter 39 inserted. in the plate circuit of the video amplifier 29, proper adjustment of the pulse delay interval can readily be discerned by the occurrence-of a dip in the meter readin as the delay interval becomes an integral sub-multiple of the original pulse interval. the delay circuit were set for. a value of 95 delay instead of a desired 99 behind the preceding pulse, the fourth pulse fed-back by the delay circuit would not coincide with the next recurrent fundamental frequency pulse. In a short time, due to this discrepancy, the video amplifier output would consist of a. great many random components all of which would addworking time to the video amplifier. and would be indicated'by the meter because of added current. Should the delay circuit be adjusted so that the delay time would be the desired 90- instead of 95, then the definite dip shown by the plate current meter would indicate that the Video amplifier would be working the minimum time of four pulses per fundamental frequency cycle.

With such a plate current indicatin device dips would occur with delay time settings of 189, 12.0", 96, '72", 60, 45, or of any other delay time union will constitute an integral submultiple of the pulse interval of the output of the. pulse forming circuit 24. As stated above the pulse width and the capabilities of the delay. circuit provide a limit to frequency multiplication which may be attained.

In using a multiplier constructed. in accordance with this invention to. drive a class 03' radio frequency amplifier. such as 34; the anode circuit of said F. amplifier is tuned'to a resonant frequency comparable to the repetition rate of the multiplied pulses driving its grid. Radio frequency energy of controlled frequency is then available in the anode circuit of the class C amplifier indicated by the graph The anode tunin of this amplifier 35 and the delay time adjustment of the delay circuit 24. can be mechanically coupled as indicated at 58, to provide a controlled output of a great number of multiples of. the frequency of" the sourceoscil lator 40.

iii)

The pulsed output of the multiplier can be used to provide precision markers for a time base, since the oscillator H) can be very stable and the delay conditions may be readily and accurately determined by use of the anode current meter 30.

The circuit illustrated in Fig. 2 differs from that of Fig.1 in that a blocking circuit 40 is inserted between the pulse formin circuit M and the delay circuit 24. The output of the pulse forming circuit I4 is fed to the blocking circuit 4.0.: through lead 42 and the blocking circuit is connected to the delay circuit 24 by lead 38 in a manner to render the feed-back circuit, of which the delay circuit is a part, inoperative during the blocking interval. The blocking circuit may be any one of a number of well known trigger circuits or synchronized multivibrator circuits;

In the operation of the embodiment illustrated inv Fig. 2 the blocking circuit 40 opcratestc render the feed- back circuit 22, 24, 23 inoperative for acontrollable period of time during each pulse interval of the output of the pulse formin circuiti i.4.. By this means puls groups of two or more pulses can be produced such as indicated by the graph 3?. Variations of pulse groupingv can be obtained by proper control: of theoperating. interval of the blocking circuit 40;

It.- will. be. evident from the foregoing. that the invention is not. limited: to the specific circuits and arrangements of parts shown and. disclosed herein for illustration but that the underlying concept and principle of the invention are susceptiblev of numerous. variations. and modificationseoining within the broader. scope and spirit thereof. as definedby the. appended. claims. The specification and. drawings are accordingiy to be regarded in an; illustrative rather than a limiting sense;

What is. claimed is:

l. A frequency multiplying system comprising means. generating a uniform train of energy pulses;v means amplifying the output of saidgencrating means; means feeding back energy from the output of saidv amplifying means to-the input thereof, saidfeed-back means comprising means delaying said energy. by an. integral sub-multiple ofthe-pulse interval of said. train, an amplifying circuit connected to amplify the output of said amplifying means, said amplifying circuit having a tuned output circuit resonant at the pulse repetition rate of said amplifying means; and ganged means for simultaneously tuning said resonant output circuit and varying the delay of said delay means, whereby said resonant output circuit is maintained tuned to the pulse repetition rate of said amplifying means,

2; A frequency multiplying system in. accordance with claim 1; said system comprising means for indicating when said delay means is delaying the energy f d-back to the. input of said amplifying means by an integral sub-multiple of the pulse interval of said train, said indicating means comprising a current meter connected to measure the output current of said amplifying means, whereby a dip in the reading of said meter indicates thatthe delay introduced by said delay means is an integral fraction of said pulse interval.

3. A frequency multiplying system comprising means generating a uniform train of energy pulses; means amplifying the output of said generating. means; means feeding back energy from the outputiiofsaid amplifying meansto the-in put thereof, said feed-back means comprising means delaying said energy by an integral submultiple of the pulse interval of said train; and an amplifying circuit connected to amplify the output of said amplifying means, said amplifying circuit having a tuned output circuit resonant at the pulse repetition rate of said amplifying means.

4. A frequency multiplying system comprising means generating a uniform train of energy pulses; means amplifying the output of said generating means, and means feeding back energy from the output of said amplifying means to the input thereof, said feed-back means comprising means delaying said energy by an integral sub-multiple of the pulse interval of said train.

5. A frequency multiplying system comprising means generating a uniform train of energy pulses; means amplifying the output of said generating means, means fe'ding back energy from the output of said amplifying means to the input thereof, said feed-back means comprising means delaying said energy by an integral submultiple of the pulse interval of said train and means measuring the output current of said amplifying means.

6. A frequency multiplying system comprising a stable pulse oscillator, a video amplifier connected to amplify the output thereof, a feedback circuit feeding energy from the output of said amplifier to the input thereof, a delay circuit forming a part of said feed-back circuit and operable to delay the energy fed-back thereby, by an integral sub-multiple of the pulse interval of said oscillator output, a current meter connected to indicate the output current of said amplifier, and a tuned radio frequency amplifier connected to amplify the output of said video amplifier.

7. A frequency multiplying system in accordance with claim 6, said system comprising means for varying the delay interposed on said fed-back energy by said delay circuit, means for varying the tuning of said tuned amplifier and means connecting said delay varying means and said tuning means for simultaneous operation,

8. The method of multiplying the frequency of an energy wave which comprises forming said wave into a uniform train of energy pulses, amplifying said pulses, extracting energy from each of said pulses after said amplification and inserting it into the portion of said train not yet amplified, said insertion being delayed by an integral sub-multiple of the pulse interval of said train, and converting said amplified train into an oscillatory wave corresponding in frequency thereto.

9. The method of multiplying the frequency of an energy Wave which comprises forming said wave into a uniform train of energy pulses, amplifying said pulses, extracting energy from each of said pulses after said amplification, inserting it after a delay into the portion of said train not yet amplified, regulating said delay to an amount such that a condition of minimum current flow exists in said amplified train, and converting said amplified train into an oscillatory Wave corresponding in frequency thereto.

JAMES F. GORDON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,442,781 Nichols Jan. 16, 1923 2,212,173 Wheeler Aug. 20, 1940 2,411,166 Olson Nov. 19, 1946 2,414,541 Madsen Jan. 21, 1947 2,416,089 Jones Feb. 18, 1947 2,429,227 Herbst Oct, 21, 1947

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