US2553219A - Superregenerator - Google Patents

Description

y 1951 J. c. TELLIER 2,553,219

SUPERREGENERATOR Filed April 2, 1946 2 Sheets-Sheet 1 F. '&

INVENTOR. JQJf/"fi C. 7224/51? BY y 1951 J. c. TELLIER 2,553,219

SUPERREGENERATOR Filed April 2, 1946 2 Sheets-Sheet 2 F/cj. a.

INVENTOR. JOSE/ h C. TELL/E1? Patented May 15, T951 SUPERREGENERATOR Joseph C. Tellier, Penn Wynne, Pa., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application April 2, 1946, Serial No. 658,894.

1 Claim.

This invention relates to improved methods of and means for operating superregenerative receivers. Application of the principles and methods disclosed herein is made, for example, in connection with the radio ranging systems described and claimed in copending applications of William E. Bradley and of Wilson P. Boothroyd and Albert L. Free, Serial Number 651,398, filed March 1, 1946, now Patent No. 2,536,346, issued January 2, 1951, and Serial Number 651.888, filed March 4, 1946,, now Patent No. 2,536,488, issued January 2, 1951, respectively. It is, however, to be understood that the invention is not restricted to use in those particular systems, but is applicable to superregenerative receivers generally and may be used to effect a substantial improvement in their operation.

The principal object of the invention is to provide methods of and means for increasing the band width and sensitivity of superregenerative receivers. Another object of the invention is to provide a circuit capable of taking advantage of such improved band width and sensitivity by making it possible to obtain the maximum discrimination between the outputs of a superregenerative receiver in the presence and in the absence of an applied input signal. Other features and advantages of the invention will become apparent after consideration of the following description and the drawings in which? Figure 1 illustrates a superregenerative re ceiver adapted to operate in accordance with the principles of the invention.

Figures 2 and 3 are diagrams which will be referred to in explaining the principles and mode of operation of the invention.

Figure 4 is a schematic diagram of a superregenerative receiver which may be made to operate in accordance with the principles of theinvention by the application of an unquenching wave form of suitable shape, hereinafter to be defined.

Referring now to Figure 1', the superregenerative receiver shown comprises a triode l' and a resonant tank circuit 2 comprising inductor 3 and condenser 4. Tank circuit 2 may be tuned to any desired frequency (e. g., 60 megacycles' per second) and determines the frequency at which the superregenerator will oscillate. A portion ofinductor 3 is made common to both grid and plate circuits of triode I in order to provide the necessary mutual coupling required for oscillation. Received signals intercepted, by

antenna 5 are supplied to tank circuit 2 through the medium of mutual coupling between in,-

2. ductors 3 and 6. Also coupled to tank circuit 2 through inductor 1' is a damping circuit comprising serially and oppositely connected diodes 8 and 9'. Between the plates of these diodes and a center tap on inductor I is provided a connection including condenser 10 for by-pass-ing signal frequencies within the range of oscillation of the superregenerator. To the plates of diodes 8' and 9' are supplied periodically recurring negative unquenching pulses of the form shown at A in Figure 2. The duration of such pulses may be, for example, of the order of 35 [1. seconds and they may be recurrent at almost any desired frequency, the frequency of recurrence having no appreciable effect on the operation of the circuits in accordance with the invention. Diodes 8 and 9 may be biased, by the application of a voltage derived across resistor ll of a voltage divider comprising resistors II and l2, so as to cause them normally to conduct and introduce damping into tank circuit 2 of the, superregenerative oscillator. At the same time the magnitude of this bias, as compared with the magnitude of negative unquenching pulses,

should be such that upon the occurrence of an unquenching pulse, diodes 8 and 9 will cease to conduct. thereby removing the damping from tank circuit 2 and permitting oscillations to build up therein. Further limitations on the value of this bias in accordance with the present invention will be set forth hereinafter. The diode quenching arrangement shown is particularly advantageous since it avoids shock excitation of the oscillator tank circuit, inasmuch as surge currents flow from each end of damping inductor T and therefore tend to cancel. This circuit is described and claimed in copending application of William E; Bradley, Serial Number 660,037, filed April 6, 1947.

Further in accordance with the invention the grid of triode l is grounded through grid leak resistor I 3 and diode l4, the latter being connected in the polarity shown. A connection, including an RC circuit comprising resistor l5 and condenser I6, is also provided between the common plates of diodes 8' and 5- and the plate of diode M. The purpose of these connections will be explained later in this specification. Output from tank circuit 2 during the unquenched intervals of the superregenerative oscillator may be derived by means of a counter circuit com-' prising condenser IT, diodes I8 and I9, condenser 2i! and resistor 2|. The mode of operation of this circuitwill be describedin detail hereinafter.

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I have discovered that in order to secure wide band operation in a superregenerative receiver, it is essential that the net conductance of the oscillator circuit be changed as rapidly as possible from a large positive value to a large negative value, in other words the change from complete quenching to complete unquenching of the oscillator tank circuit should be made in as short a time as possible. Assume for the moment that, in the circuit of Figure 1, the bias for diodesB and 9 is provided solely by the RC circuit comprising resistor II and condenser 22 (i. e. that resistor I2 of the voltage'dividerll, I2 is not connected to an external source of biasing volt- Assume further that the grid of triode I is connected directly to ground through grid leak l3 and that both diode I 4 and the connection,

comprising RC circuit I5, I6, between the plates of diodes 8 and 9 and the p ate of diode I4 is omitted. Exaggerating the imperfections inherent in the leading edge of the negative unquenching pulse shown at A in Figure 2, it may appear as shown in Figure 3. The leading edge will have a finite slope, and the upper and lower corners will be somewhat rounded as shown. Assuming the quenching wave form to vary from a value of 250 volts positive (corresponding to quenching) to a value of 180 volts positive (corresponding to unquenchin L'there will normally be deve oped across condenser 22 a biasing voltage of approximately +250 volts which will be applied to the cathodes of diodes 8 and 9 and will permit them normally to conduct and introduce damping into tank circuit- 2. As the quenching voltage fal s from 250 volts by an amount AE (which may be of the order of 5 volts), the change in the tank circuit from its quenched to its unquenched condition will take place during an interval AT, which owing to the gradual change in slope of the quench wave form as represented in Figure 3, may not be sufliciently short to yield the desired wide band-width. By applyin to the cathodes of diodes 8 and 9, through the medium of voltage divider I I, I2, a somewhat less positive bias (e. g. +245 volts), the change from the quenched to the unquenched condition, corresponding to the change AE, may be made to take place in an appreciably'shorter interval AT as illustrated in Figure 3. This diminution in the time required for unquenching will result from operating on the steeper portion of the quench wave form. Thus, by properly adjusting the bias on diodes 8 and 9, two objectives may be achieved; first, the unquenching of the superregen rator may be made to occur more rapidly, and secondly, the exact time of 'unquenching may be controlled within limits by varying the bias.

. The effect of changing the net conductance of the oscillator circuit from a large positive to a large negative value at the inception of the unquenched interval will be to cause oscillations to build up in the oscillator tank circuit more rapidly than they otherwise would, both in the presence as well as in the absence of signals applied to tank circuit 2 from an external source such as antenna 5. However, the rate of exponential buildup will also vary, depending upon the magnitude, if any, of such signal present in the tank circuit at the time of unquenching. In the absence of any such signal, oscillations in the tank circuit might build up to an amplitude 41 corresponding to tube overload during an interval T1 as illustrated at B in Figure 2. Oscillations in tank circuit 2 would then continue at this amplitude during the remainder of the unquenched in.'

terval T4. On the other hand, with some signal present in tank circuit 2 at the time of unquenching, buildup to tube overload would occur in a time substantially less than T1, as illustrated at C in Figure 2. In this instance likewise, once having built up to overload amplitude, oscillations would continue in the tank circuit throughout the unquench interval of duration T4.

The principal effect of permitting oscillations to continue in the tank circuit, after they have reached an amplitude sufiicient to produce overload in triode I, is to reduce the percentage difference between the envelopes of the oscillations in tank'circuit 2 corresponding respectively to absence and presence of signal in the tank circuit at the time of unquenching. This will be apparent from a comparison of B and C in Figure 2.

Thus, using a cycle counter of the sort shown in Figure 1 to distinguish between the outputs from the superregenerative oscillator in the presence and in the absence of received signal, it will be more difiicult to distinguish received signal from noise (i. e. the sensitivity of the receiver will be appreciably reduced). This reduction in sensitivity may be overcome by effectively reducing the duration of the unquenched interval of the superregenerator. I have found it desirable, for example, to make the unquench interval of the same order of magnitude as the time required for oscillations in the tank circuit to build up to the overload condition in the absence of any appreciable signal externally applied to the tank circuit. If, for example, the unquench interval is made equal to the time required for oscillations to build up to overload in the absence of received signal, the enve ope of oscillations in the tank circuit corresponding to no externally applied signal will be as represented at D in Figure 2. Similarly the envelope corresponding to the presence of externally applied signal at the time of unquenching will be as represented at E in Figure 2. Clearly the percentage difference in area under these two envelopes will be greater than in the instances represented at B and C. A cycle counter of the form shown in Figure 1 will be capable. of developing a much greater difierence in outputs for the two conditions.

Without reducing the actual duration of the negative unquenching pulses applied to the superregenerator of Figure 1, the effective duration of the unquenched interval can be reduced by the action of RC circuit I5, I6 and diode I4. While. the quenching wave form is at a value of 250 volts, diode I4 will conduct and a corresponding voltage will be developed across condenser I6. Triode I will be in a zero bias condition because of the fact that the lower end of grid leak I3 will be effectively connected directly to ground through the diode, and accordingly no grid bias will be developed inasmuch as oscillations are prevented by the damping applied to tank circuit 2. As the voltage applied to the plates of diodes Band 9 commences to decrease upon the inception of the unquench interval, the plate of diode l4, due to the action of RC circuit [5, l6 which has a relatively long time constant, will go negative by a corresponding amount so as to cut off diode HI. Initially there will be no change in the bias ap-- plied to the grid of triode I since, for small changes in applied bias introduced in series with an oscillator grid leak, the tube will tend to read just'itself by change in grid current to the preexisting bias condition. As the reduction in quenching voltage continues, diodes 8 and 9 will b 9 1C911 so as to rem v the dampin an 1 r the tank circuit is undamped, and I have found that the intervening interval is sufficient to .permit the reqired buildup of oscillations in the tank circuit. The duration of this interval can be controlled by varying the slope of the unquenching pulses, by varying tube characteristics and by adjustment of the biasing voltage applied to diodes 8 and 9 from voltage divider l I, I2. Thus, if desired, the interval may be made of the same order of magnitude as the time required for oscillations to build up in the tank circuit 2 in the absence of externally applied signal.

With the circuit as described operating at an oscillator frequency of 60 megacycles per second and with an effective unquench interval of 1 p. second duration, a bandwidth of 3 megacycles per second was achieved. Furthermore it was found that, because of the relatively short unquench interval, a higher plate voltage could be used without exceeding the permissible plate dissipation of the oscillator tube. With higher plate voltage, a larger negative conductance is obtainable which further tends to increase the band width.

Although, as illustrated in Figure 2, the interval, during which oscillations are permitted to build up and exist in tank circuit 2, is made equal to the time required for oscillations to build up to overload in the absence of signals impressed on the tank circuit from an external source, the duration of this interval may be varied appreciably while still retaining the advantages of operation in accordance with the invention. Thus, under certain circumstances, it may be found desirable to make the effective unquenched interval appreciably shorter, corresponding to time T2 as shown in Figure 2; while under other circumstances it may be desirable to make the interval somewhat longer, corresponding to time T3. In varying the duration of the interval, however, it should be borne in mind that permitting oscillations to continue after overload has been reached will, in general, tend to reduce the difference between the output in the presence and in the absence of externally applying signal. Furthermore, it may be noted that, if logarithmic output versus input is desired, the unquenching interval should be of duration at least suiiicient to permit oscillations to build up to overload in the presence of an externally applied signal of maximum amplitude.

Alternatively, the results achievable from the circuit of Figure 1, which are independent of the duration of applied negative unquenching pulses, may be obtained in accordance with the invention by applying, to any superregenerative receiver, negative unquenching pulses having leading edges of the desired steepness, and of duration equal to that required to effect the desired mode of operation. Thus, in order to secure the mode of operation represented at D and E of Figure 2, negative pulses corresponding to the one represented at F in Figure 2 might be applied to a superregenerative oscillator such as the one shown in Figure 4. This circuit differs from that of the schematic of Figure 1 only in the omission of diode l4 and RC circuit I5, l6 and in the use of self bias for diodes 8 and 9 derived from RC circuit 'l I, I! in lieu of bias from an external source.

unquenchin pulses may be obtained through the utilization of any conventional means external to the oscillator circuit. Thus, as set forth in the aforementioned copending applications, if unquenching pulses of longer duration and insufficient steepness are available, they may be shortened and steepened by differentiation to yield pulses of the desired duration and steepness.

Returning now to consideration 'of the cycle counter circuit shown in the schematic of Figure 1, for deriving an output signal from tankcircuit 2 of the superregenerative oscillator, this circuit operates to develop across condenser 20 an integrated unidirectional potential which increases with the number and amplitude of individual cycles of the signal appearing in the oscillator tank circuit. Its operation is briefly as follows:

During each positive oscillator cycle, condenser 20 is charged through condenser I1 and diode l9. If condenser 20 is made times as large as condenser [1, an increment equal to l/ 101 of the peak tank circuit voltage will be developed across condenser 2|] during each cycle. It will thus be apparent that the magnitude of condenser II should be small by comparison with that of condenser 20. On negative half cycles condenser I! will be discharged through diode [8. The voltage developed across condenser 20 will approach the peak tank circuit voltage after a sufiicient number of cycles. Thus, with a signal in the tank circuit of 1 a second duration, corresponding to that shown at E in Figure 2, there way be the equivalent of 60 complete half cylces at the oscillator frequency of 60 megacycles. This will result in the development, across condenser 20, of a voltage equal to 0.6 of the peak tank voltage. In the absence of any applied signal, on the other hand, the tank circuit signal may be equivalent to only five complete half cycles, and the voltage developed across condenser 20 will be 0.05 times the peak tank voltage. If the peak tank voltage is 10 volts, an increase of 6 volts will be developed in the presence of signal. The time constant of the circuit comprising condenser 20 and resistor 2| should be relatively long compared to the unquenched interval but short by comparison with the interval between unquenching pulses.

I claim:

An electrical circuit for detecting the energy content of successive pulses of oscillatory energy, said pulses having a predetermined maximum duration and a predetermined minimum timespacing therebetween, said circuit comprising: a pair of input terminals for said successive pulses of oscillatory energy; a charging condenser and a first unilateral conductive device serially connected between said input terminals; a series combination of a storage condenser and a second unilateral conductive device connected in parallel with said first unilateral conductive device, unlike elements of said first and second unilateral conductive devices respectively being connected together at the common connection of said charging condenser and said first unilateral conductive device, the capacity of said storage condenser being large compared to the capacity of said charging condenser; and a resistor connected in parallel with said storage condenser, the value of said resistor being such, in relation to the capacity of said storage condenser, that the time constant of said resistor and said storage condenser is longer than said maximum The proper duration and steepness of tent of corresponding oscillatory pulses supplied to said input terminals.

JCSEEH C. TELLIER.

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

8 UNITED STATES PATENTS Number Name Date 2,076,168 Turner Apr. 6, 1937 2,357,932 Crosby Sept. 12, 1944 2,403,557 Sanders July 9, 1946 2,403,615 Sanders 1 July 9, 1946 2,410,768 Worcester Nov. 5, 1946 2,412,710 Bradley Dec. 17, 1946 2,419,569 Labin Apr. 29, 1947 Miller May 11, 1948 I OTHER REFERENCES Frink, Basic Principles of Superregenerative Reception, Proceedings I. R. 152., vol 26, January, 15 1938.

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