March 13, 1962 .J. E. DURKEE 3,025,394 'SUPER-REGENERATIVE TRANSISTOR DETECTOR Filed May 15, 1958

|n INVENTOR. JOHN E. DURKEE BY - amass nited States Patented Mar. 13, 1%32

1 2 3,025,394 pacitance of the transistor is used to provide the re SUPER-REGENERATIVE TRANSISTOR DETECTQR generative feedback path, but the strength of the signal John E. Durkee, Conesus, N.Y., assignor to General Dy is maintained ‘below the oscillatory level by the external namics Corporation, Rochester, N.Y., a corporation of capacitance which ‘bleeds off a portion of the feedback Delaware signal. Filed May 15, 1958, Ser. No. 735,611 In accordance with another aspect of the invention, 2 Claims. (Cl. 250-20) the regenerative detector circuit is made super-regenera tive by incorporating therein a relaxation type oscillator The present invention relates to radio receivers and it circuit to provide the quench frequency signal which relates more particularly to a new and improved detector 10 periodically causes the detector circuit to oscillate. Op circuit which is both ef?cient and reliable in operation eration of the detector in this manner thus greatly in and which utilizes relatively few components so as to be creases its gain and reduces the number of additional small in size, simple in construction, and inexpensive to stages of audio ampli?cation which are required for driv manufacture. - ing the speaker. Radio‘ receivers which are sufficiently small to ?t in 15 Many other objects and advantages of the present in one’s pocket or, perhaps, to be strapped to the wrist, have vention will become apparent from a consideration of many important uses such, for example, as a primary the following detailed description when taken in conjunc component in paging systems of the type presently used tion with the following drawing which is a schematic in industrial plants, hospitals and the like. Moreover, circuit diagram of a radio receiver embodying the present such receivers can be carried by ?remen during the ?ght 20 invention. ing of a ?re to provide direct communication between Referring now to the drawing, a radio receiver Jiii a number of ?remen and a central station from which comprises an antenna coil 11 which intercepts an ampli ?re ?ghting directions are given to the individual ?re tude modulated radio signal to develop therein a current men. In this latter application the receivers must be varying in accordance with the radio signal. A ?xed so small in size and light in weight as not to interfere, 25 capacitor 12 and an adjustable trimmer capacitor 13 are in any appreciable way, with the activities of the ?re connected in parallel across the antenna coil 11 to pro men, but they must also be extremely reliable in oper vide the usual tank circuit which is adjustably tunable ation to insure that the communication links between the to select a desired signal from the various radio frequency central station and the individual ?remen is maintained at all times. signals which are intercepted by the antenna coil 11. 30 Where the radio receiver 10 is designed for operation at In order to minimize the number and size of the circuit a single frequency, the capacitor 13 is not ordinarily ad~ components used in the receiver, it would be desirable justed during normal use of the receiver but should be to employ a super-regenerative detector circuit using a adjusted at the factory. transistor. The advantage of a super-regenerative de The receiver v10 is energized by a battery 14 having tector circuit is that a maximum gain is achieved with 35 the positive pole thereof connected to ground through a the smallest number of components, and the provision receiver on-otf switch 15. The switch 15 is a simple, of the transistor reduces the size of the receiver because single throw, single pole switch which is shown in the a transistor is considerably smaller than a comparable “off” position. Therefore, with the switch 15 in the tube, and a very small battery may be employed because “on” position, the antenna circuit is connected between of the relatively low power drain of the transistor. 40 the negative pole of the'battery 14 and the collector of Therefore, an object of the present invention is to pro a PNP junction transistor 16 whose base is connected to vide a new and improved radio receiver. the positive pole of the battery 14 through the ground Another object of the present invention is to provide connection. As shown, the antenna coil 11 is connected a new and improved radio'receiver which is operable in the UHF frequency band. 45 to the negative pole of the battery 14 through the primary winding of an audio frequency coupling transformer 17 A further object of the present invention is to pro and the base of the transistor 16 is connected to ground vide a new and improved super-regenerative detector cir cuit. through the parallel circuit comprising a capacitor 13 and 'a pair of resistors ‘19 and 20. If the receiver 10 is A further object of the present invention is to pro 50 to be used in a system employed in ?ghting ?res, it is vide a new and improved super-regenerative detector cir desirable that it operate in the UHF frequency range cuit using a transistor as the nonlinear impedance ele such as, for example, at a frequency of 41.6 megacycles ment. I which is the frequency'allotted by the Federal Com Another object of the present invention is to provide munications Commission ‘for this purpose. Accordingly, a new and improved quench circuit for use in conjunc it is necessary to select a transistor 16 which may be tion with a radio receiver employing a super-regenerative 55 detector. operated at this high frequency and it has been found that certain types of transistors such, for example, as Brie?y, the above and further objects are realized in the surface barrier transistors satisfy this requirement, accordance with the present invention by operating a but the internal capacitance between the collector and transistor detector at a su?iciently high frequency that 60 the emitter thereof, which is designated in the drawing the internal capacitance between the electrodes of the by the number 22, provides suf?cient feedback to cause transistor provides su?icient regenerative feedback to oscillation of the transistor 16. For voice transmission cause the transistor circuit to oscillate, and reducing the purposes, this is, of course, undesirable, and therefore, amplitude ofthe feedback‘ signal below the oscillatory it is necessary to prevent the transistor 16 and its as level by means of a capacitor connected between one of 65 sociated circuit components from continuously oscillat the electrodes and ground. In this way the internal ca ing at these high UHF frequencies. Consequently, and 3,025,894 4 3 components are very small in size and provide a low cur in accordance with the present invention, the variable rent drain on the battery. Consequently, a small, reli capacitor 24 is connected between ground and the emit able, and inexpensive radio receiver may be designed in ter of the transistor 16 thereby to bleed off an adjustable corporating the detector and quench circuit of the pres portion of the signal which is fed back from the collector ent invention. to the emitter through the internal capacitance 22. That By way of illustration only, and not by way of limiting is, capacitances 22 and 24 constitute a voltage divider this application thereto, the following component values and the carrier potential across capacitance 22, and hence have been found to give ef?cient operation in a particu the degree of carrier feedback, may be controlled by lar construction of the disclosed radio receiver. properly selecting the value of capacitance 24. A direct current path around the capacitor 24 is provided prefer 10 Transistor 16 ______SBl03. ably by a high inductance coil 24a. Continuous oscilla Transistor 30 ______2N l 32. tion of the detector circuit may thus be prevented by Resistor 19 ______. 2700 ohms. properly adjusting the capacitor 24. If it were desired Variable resistor ______1200 ohms maximum. to operate the detector circuit including the transistor Resistor 29 ______. 1 kilohm maximum. 16 as a regenerative detector, the value of the capacitor 15 Capacitor 12 ______. 62 micrornicrofarads. 24 would be adjusted such that the gain of the feedback Capacitor 13 ______»__-_ 5—25 micrornicrofarads. loop including the internal capacitance 22 were slightly Capacitor 18 ______. .005 microfarad. less than unity thereby to provide maximum gain without Capacitor 24 ______5-25 micromicrofarads. any oscillation. Capacitor 3‘1 ______.01 microfarad. While a substantial amount of ampli?cation may be 20 Capacitor 33 ______25 microfarads. provided by the detector 16 when it is operated regenera Capacitor in trap 28 ______. .01 rnicrofarad. tively in this manner, it would be desirable to further Conductor ‘in trap 28 ______10 millihenries. increase the ampli?cation thereof if such would reduce While there has been described what is at present the required number of audio stage ampli?cation. Con 25 considered to be a preferred embodiment of the inven sequen-tly, in accordance with the present invention the tion, it Will be understood that various modifications gain of the detector is substantially increased by operat may be made therein which are within the true spirit ing the transistor 16 super-regeneratively. and scope of the invention as de?ned in the appended In order to periodically render the detector circuit claims. oscillatory at a quench frequency which is substantially 30 What is claimed as new and desired to be secured by less than the signal frequency, a blocking type oscillator Letters Patent of the United States is: including the capacitor 18 is provided for periodically l. A super-regenerative detector circuit comprising varying the potential at the base of the transistor 16 be a transistor including base, collector, and emitter elec tween a value at which the detector oscillates and a trodes; an input circuit for modulated radio frequencies value at which it is stable. Considering the operation of 35 connected between said base and collector electrodes; the detector circuit of the present invention, assume that an output circuit connected to said collector electrode; the switch 15 has been open for some time and is at this a regenerative circuit coupling said collector and emitter time initially closed. The capacitor 18 is discharged and electrodes and consisting solely of the internal capacitance the base of the transistor 16 is, therefore, at a negative po of said transistor; ?rst capacitive means connected be tential determined by the values of the resistors 19, 20, and 40 tween said base electrode and reference ground and 26. The signal received by the antenna system is sup with means for controlling the bias on said base electrode; plied to the emitter of the transistor 16 and is detected resistance means connected to said emitter electrode, said to develop the audio modulation voltage across the pri resistance means and the base-to-emitter path of said mary winding of the transformer 17. Because of the transistor providing a discharge path for said ?rst capaci base of the transistor 16 is more positive than the col tive means, the time constant of said resistance means lector, the detector does not immediately go into oscil and said ?rst capacitive means substantially determin lation. However, as the capacitor 18 charges up, the ing the quench frequency of said detector circuit; and potential of the base increases in a negative direction second capacitive means shunting said resistance means until the value is reached at which the detector 16 oscil to by-pass the signal supplied to said emitter electrode by lates. When it does, the emitter-to-base current flows 50 said regenerative circuit, and a third capacitive means which quickly discharges the capacitor 18 thereby to in connected directly in series with said emitter electrode crease the potential of the base above the value at which and with the inherent collector-to-ernitter capacity of oscillation takes place. Oscillation is thus terminated said transistor to control regenerative feedback from and the capacitor again is gradually charged up to a said emitter electrode to said collector electrode. value at which oscillation again occurs. 2. A super-regenerative detector circuit comprising a Because the capacitor 18 discharges ‘through the emit transistor including a ?rst, a second and a third elec ter circuit to ground during oscillation of the transistor trode, an input circuit for modulated radio frequencies 16, an adjustable resistance 29 may be connected between connected between said ?rst and said second electrodes, ground and the emitter of the transistor 16 Ito control an output circuit connected to said second electrode; a re the quench frequency. The resistor 29 must, of course, 60 generative circuit coupling said second and said third be bypassed by a pair of capacitors ‘31 and 33 to con electrodes ‘and consisting solely of the internal capaci nect the bottom of the capacitor 24 substantially at tance of said transistor; ?rst capacitive means connected ground potential for bleeding off a portion of the UHF between said ?rst electrode and reference ground and feedback signal. with means for controlling the bias on said ?rst elec The detected signal which, together with the received 65 trode; resistance means connected to said third elec UHF signal appears in the collector circuit, is coupled trode, said resistance means and the ?rsteto-third electrode through the transformer 17 and an LC resonant circuit path of said transistor providing a discharge path for 28 to an audio ampli?er comprising a transistor 30 in the said ?rst capacitive means, the time constant of said re collector circuit of which is connected the voice coil 31 sistance means and said ?rst capacitive means substan of a loud-speaker 32. The loud-speaker 32 is preferably 70 tially determining the quench frequency of said detector contained in an ear plug to minimzie the power require circuit; and second capacitive means shunting said re sistance means to by-pass the signal supplied to said ments of the receiver. The present invention thus provides a super-regenera third electrode by said regenerative circuit, and a third tive detector circuit employing a transistor thereby to capacitive means connected directly in series with said provide high gain with a minimum of components, which 75 third electrode and with the inherent second-to-third 3,025,394 5 6 electrode capacity of said transistor to control regenera 2,821,625 Price ______Jan. 28, 1958 tive feedback from said third electrode to said second electrode. 2,863,995 Chow ______Dec. 9, 1958 2,922,032 Hass et a1. ______Jan. 19, 1960 References Cited in the ?le of this patent OTHER REFERENCES UNITED STATES PATENTS Pub. 2-Eleotron-ics, August 1953, pages 170-173, I unotion Transistor Applications, by Sulzer. 2,576,642 Richman ______Nov' 27, 1951 Pub. 1——Transaotions of The Institute of Radio Engi 2,751,447 Duncan ______June 14, 1956 neers, Professional Group on Electronic Devices, vol. 2,789,214 Seatgeant ______Apr. 16, 1957 0 ED~1, No. 2, pages 43-52, April 1954; A Point Contact 2,792,494 Suran et a1. ______May 14, 1957 Transistor VHF FM Transmitter, by D. E. Thomas.