Патент USA US2135599код для вставки
Nov. 8, i938. H. o. PETERSON 2,135,599 AUTOMATIC VOLUME CONTROL CIRCUIT Filed Sept. 14, 1935 ti qniw k $17K \NN +w/lk " _v A‘“.1 < $5_1\0-$- “ _ / m m, h . \M4 INVENTOR M _ HAROLD o. PETERSON B Y "i QMW ATTO R N EY Patented Nov. 8, 1938 2,135,599 UNITED STATES PATENT OFFICE , v 2,135,599 AUTOMATIC VOLUME CONTROL CIRCUIT Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware‘ Application September 14, 1935, Serial No. 40,568 5 Claims. My present invention relates, in general to automatic gain regulation circuits adapted for use in connection with signal ampli?ers and radio receivers, and more particularly the invention 5 relates to automatic volume control ‘circuits uti lizing diodes as signal detectors and gain control devices. Diode recti?ers are often utilized at the present time as signal demodulators of radio receiving '10 systems. Such .diode‘ devices are, also, suitable for use as signal recti?ers in connection with automatic volume control circuits in order to maintain a substantially constant signal ampli tude at the demodulator input circuit. In the 15 ‘past a common diode device has been used both for the signal detection and automatic volume control recti?er functions. However, many of these past devices have been constructed so as torequire the diode anode to be maintained nor 20 - mally at a negative direct current potential with respect to the cathodes of the signal transmis 2 sion tubes whose gain was under control. According to one of the main objects of my present invention, a diode recti?er device is uti lized'to demodulate the received signal, and si dicated diagrammatically a circuit organization whereby my invention may be carried into effect. Referring now to the accompanying drawing, which shows the present invention embodied in a receiver of conventional construction, it will be observed that the numeral I designates a signal collector device. This device may be the usual grounded antenna, or it may be a loop antenna; dipole or even a radio frequency signal distribu tion line. The collected signals, which signals 10 may be in the broadcast range or any of the short , wave ranges, are impressed on the tunable input circuit 2 of the radio frequency ampli?er tube 3. The tube 3, shown as a screen grid tube of the indirectly heated cathode type, has its cathode 4 15 grounded, and it will be understood that the screen grid and plate of the tube are connected to suitable sources of positive direct current po tentials. Such sources are not shown, but those skilled in the art are-fully aware of the fact that 20 these sources may be of the battery type; or they may be embodied in the usual bleeder resistor connected across the ?lter output of a 60 cycle alternating current recti?er. ' A grounded electrostatic shield 5 is shown dis multaneously to rectify signal energy for the posed between the signal collector l and the input production of a gain control voltage which is used to decrease the gain of the signal ampli?ers as coil of the tunable circuit 2, and it will be under~ stood that the numeral 6 designates a tuning device which is used to tune the radio receiver the received signal amplitude increases, the diode at = (Cl. 250-20) 25 anode being normally maintained at a potential through the desired operating frequency range. which does not becomenegative, and which spe ci?cally is positive, in direct current potential with respect to the cathodes of the controlled The signal demodulator, or detector, is a triode of the indirectly heated cathode type, which may be, for example, a tube of the 37 type, and is des ignated by the numeral 1. To provide a diode detector device the grid and plate of tube 1 are 35 tubes. , Another important object of the present in vention may be said to reside in the provision of a'radio receiving system wherein a signal trans mission tube has its normal negative grid bias provided by the conjoint and opposing action of 40‘ negative and positive direct current voltage sources, and wherein the normal negative grid bias is increased, as the rec-eived'signal amplitude increases, by a diode signal recti?er whose anode is normally maintained positive with respect to 45 the cathode of the controlled tube. Still other objects of the invention are to im prove generally the simplicity and [efficiency of radio receivers utilizing automatic volume con trol, and more especially to provide such radio 50 receivers with diode signal detectors in such a manner that the receivers are not only reliable and efficient in operation, but economically manufactured and assembled. The novel features which I believe to be char 55 acteristic of my invention are set forth in par ticularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in 60. connection withthe drawing in which I have in strapped together, and the resulting diode out put electrode is connected to the cathode 8 through a path which includes the signal input coil 9, the coil ID, the condenser ll, resistor R2 and the visual indicating meter, or milliammeter 40 l2. The condenser l3, connected between the high alternating potential side of coil 9 and ground, tunes coil 9 to the operating signal fre quency which is to be detected. A heating bat tery A is connected across the heater element 14 45 of diode 1, and the positive terminal of the heat ing source A is connected to the ungrounded side of resistor R2 through the choke coil l5, which, of course, has ?nite resistance. The audio frequency utilizing network, which 50 may comprise one or more stages of audio fre quency ampli?cation followed by a reproducer or other signal indicator, has impressed upon it the demodulated signal energy through a path which includes the audio frequency transformer 55 [6. The primary winding ll of transformer 16 has one side thereof connected to the junction of coils 9 and ID through a path which includes coil l8. The resistor R6 is connected in shunt with winding H, the condenser (9 being con 60 2,135,599 ' 2 nected in series with winding I ‘I and resistor R6. The by-pass condenser 20 connects the resistor side of coil l8 to ground, and the side of resistor R6 adjacent condenser 19 is connected to ground through a path which includes resistor R4 and resistor R5. may be applied to any of the additional signal transmission tubes preceding theg?nal signal de modulator. Thos'eskilled in the. art will, in gen eral, understand the operation of the automatic volume control arrangement shown herein. Nor The junction of resistors R4 and R5- 4 mally,'and in the absence of received signals, the is connected to the positive terminal of heating automatic volume control arrangement is not source A through a path which includes resistor "functioning. ‘When the desired signals are re R1 and lead 2|. Coil l0 and condenser I l resonate - ceived, the AVG network begins to increase the 10 to the frequency of the carrier being recti?ed negative biason the signal grid 4’. As the signal 10 by the detector, This affords a low impedance amplitude increasesfthe gain control bias in path for the carrier frequency. The resistance Re I creases, and'in‘this way the gain of the signal is low compared to the primary impedance of ‘transmission tube 3 is decreased. In other words, transformer l6. Consequently, the alternating duringperiods when no signals are received the 15 and direct current impedances of the diode load circuit are substantially equal. This is a desirable condition for diode operation when signalshaving nearly 100% modulation are received. _ The gain control direct current voltage derived 20 from the recti?ed signal energy is impressed upon the signal input grid 4’ of ampli?er 3 through a path which includes the ?lter resistor R3 and lead 22. The lead 22 is denoted by the reference 4 letters AVC to designate that this is the auto 25 matic volume control circuit, and the network comprising resistor R3 and condenser 23 functions to suppress ?uctuating current components in the gain control voltage.v 30" ’ ‘ gain of the signal transmission tube 3 is a maxi 15 mum, and the receiver is in a highly sensitive condition. The cold electrode of the diode de tector ‘! is maintained normally;that is to say in the absence of desired signals, at a positive po tential with'respect to the grounded cathode 4'. This positive potential may be, for example, of. the order of 0.47 volt, and is supplied from the positive terminal of the heating’ source-A. The latter has a voltage of about 6 volts. This heat ing source not only supplies heating current to‘ the ?lament of the detector 1, but, also, impresses a potential-across the resistors R1 and R2. The approximate voltages at the'ungrounded sideof' , Signal energy is impressed between the signal grid 4' and cathode‘ 4 of ampli?er V3’by virtue of’ the connection of the signal grid 4' to the high alternatingpotential side of input circuit 2, and the signal byepass condenser 3’ connected between the low alternating potential side of in 353 put circuit 2 and ground. The desired signal energy-is transmitted to the tuned input‘circuit 9 of the diode demodulator I through the signal transmission network generally denoted by the numeral 30. Thisnetwork 30 may comprise one, or more, additional stagesv oftunable radio fre-, quency ampli?cation. In such case the tuning condenser 6, thetuning condenser l3, and the tuning condensers of the additional transmission stages may all be uni-controlled in the'wellknown 451; manner so that allsignal stages are simultane resistor R2, and at the junction ‘of resistors R1 and Rs'are shown in the drawing? Thus, the 30" junction of resistors R1 and 1251s at approximately 0.5 volt, and the ungrounded side of resistor R2 is at a potential of 1.5 volts. There is consider able voltagev drop across coil l5 due to its re ' sistance. Asa consequence of these potential relations, the AVG action does not, in the absence of desired signals’, maintain the signal grid 4' highly nega tive’;' on the other’ hand, it maintains the signal grid!’ at a relatively small negative potential with respect to‘ the grounded cathode 4, and rather close to zeroidirect current potential, with there sult‘that during periods ofitim'e'when‘no signals are impressed upon‘the collector 'Lthe signal ampli?ers are in condition to produce maximum ampli?cation of the received signals. This fol ously tuned to a desired signal frequency. . The receiver may be of the superheterodyne. type. In such a case the network 30 may com prise additional signal frequency ampli?er stages, 50 followed‘ by the usual ?rst detector and local oscillator circuits for the production of a de sired intermediate, frequency. The ?rst, detector lows by virtue of the fact that the cold electrode of the diode »'| is normally maintained at a posi-'-' tive potential with respect to the grounded oath-' ode 4. ' ' ' 503 That is to say, while the junction point of re: sistors R1 and Rs'is at approximately +0.5 volt, output will be followed by one, or more, stages the signal grids of the controlled ampli?ers are of intermediate frequency ampli?cation, A sec-' not positive by'this amount, but in fact are at a 55 ond converter can beused to change the ?rst small negative potential with respect to the I. F. (say 300 kc.) to a second I. F. (say 50 kc), grounded ‘cathodes of the controlled signal trans and the latter will be ampli?ed before detection. mission tubes. This is explained by the fact that In that case the demodulator 1 functions at inf when the cathodes of the signal transmission termediate frequency; Of course, the condenser tubes are heated to an electron emitting condi l3 in the case where the receiving system is of the tion, electrons leave the cathodes at such high superheterodyne type is ?xed in value to tune velocities that they impinge upon the signal con a the input circuit of the detector to the desired trol grids adjacent them. This causes a certain intermediate frequency. Reference is made to amount of recti?cation action, the recti?ed grid‘ 7 so the application'of J .~B. Moore, ?led December 8, 1933, and having application Serial No. 701,435, Patent No. 2,078,769, April 27, 1937, which shows a radio receiving system of the superheterodyne type with‘ which an automatic volume control “ arrangement of the present type may be em ployed. ~ While the present circuit diagram shows the AVG voltage applied to only‘ one of the signal transmission tubes of the receiving system, it will be clearly understood that the gain control biasv currents flowing through the path including re sistors R3, R4, R5 and then to ground. Normally, this recti?ed grid ‘current would maintain the signal grids of the controlled transmission tubes at a negative potential with respect to- their cathodes in the absence of received signals. This negative potential is reduced very slightly'b'y the 70 opposition of ‘the positive voltage of 0.5 volt ex isting at the junction of resistors R1 and B5. In this condition the control grid bias of these tubes assumes a value between _0.5 and -1‘.2 volts.- This assumed bias happens to be of a value 75 2,135,599 at which these tubes have approximately maxi mum gain.‘ As received signal strength is in creased irom zero, the junction of resistors R6 and R4 decreases in positive potential, goes through zero potential, and then increases in neg ative potential. The bias of the controlled tubes is practically unchanged until the potential of the junction of Re and R4 reaches a negative value 61 equal to the negative value assumed by those grids in the no-signal condition. As the signal strength is further increased the grid bias of the con trolled tubes will be the same negative potential , as that of junction Re and R4 since for such in creasingly negative values, no current will be drawn by the grids of the controlled tubes. From this point on, the gain is progressively decreased as the signal amplitude increases. In this way the signal amplitude at the input circuit of de tector l is maintained substantially uniform in spite of a wide range of signal amplitude variation at the collector I. It will be recognized that the action described above is a form of delayed AVC. The junction of resistors R6 and R4 is at positive potential for zero signal; and is at a negative potential for signals of such strength that the di rect current voltage drop in R4 is greater than the ?xed bias on R5. R3 is normally between ten times and one hundred times as great as R4 and R5. Also R3 is great compared to the internal 30 resistance between grid and cathode of the con trolled ampli?er tubes when the grids are oper ated at potentials such that grid current ?ows. For this reason the grids of the controlled stages V21 C11 become less negative only very slightly for changes in the potential of the junction of R6 and R4 as long as the potential of this junction is such that grid current will ?ow through R3. As soon as this junction becomes suf?ciently negative so that no grid current ?ows through R3 there 40 is no potential drop in R3, and, consequently, from then on to much more negative Values of the 3 to the grid of said transmission tube in a sense such that the said normal negative grid bias is increased as the received signal amplitude in creases. 2. A radio receiving system including a con trolled electronic transmission stage, a diode de tector with its anode and cathode both normally at positive potentials with respect to the cathode of the controlled electronic transmission stage, a load circuit and network connected to the diode so as to obtain modulation frequency output as Well as direct current output, the direct current output being connected in series with a ?xed source of positive direct current potential and a series resistor between the grid of the con trolled electronic transmission stage and the cathode of the latter whereby the grid of said stage will normally assume a substantially con stant potential negative with respect to the oath ode of said stage until the received signal reaches such a value that the negative direct current out put of the diode exceeds the above mentioned series ?xed source of positive potential. 3. In a signaling system having at least one signal transmission tube, a diode, means for nor- a, mally establishing the anode and cathode of the diode at positive potentials with respect to the transmission tube cathode, means for deriving from'the recti?ed output of the diode a direct current voltage, means including a source of 30 substantially constant positive potential and a source of negative potential in circuit with the transmission tube grid circuit for establishing a normal negative bias on said transmission tube, said direct voltage deriving means being con nected to the transmission tube grid circuit in such a manner that said normal negative bias value is increased when the magnitude of the derived voltage exceeds that of the positive poten tial. 4. In combination with a signal transmission 40 junction it will be found that the grids have the tube, means including opposed positive and nega same potential as the junction of Re and R4. tive direct current voltage sources for establish ing a normal negative bias on the signal input electrode of said transmission tube with respect 45 to the cathode thereof, said sources being inde pendent, and the negative source comprising a network included in circuit with said input elec trode and through which network current ?ows for signals below a predetermined amplitude, a The voltage supplied at the junction of coil l5 and R2 could be supplied by a tap on a bleeder resistance across a recti?er output deriving power from the main supply. Likewise, the usual alternating current power supply bleeder resistor may be used to supply the positive potential in dicated at the junction of R1 and R5. While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my inven tion is by no means limited to the particular or 55 ganization shown and described, but that many modi?cations may be made without departing from the scope of my invention,-as set forth in the appended claims. What I claim is: 1. A radio receiving system of the type includ ing a signal transmission tube followed by a sig nal recti?er of the diode type, means for estab lishing a normal negative grid bias for said trans 60' mission tube by the conjoint and opposing action of'indep'endent negative and positive direct cur rent voltage sources, said negative voltage source comprising a circuit in the grid circuit of the transmission tube and through which grid cur rent ?ows in the absence of signals of a desired 70 amplitude, means for preventing the recti?er anode from assuming a direct current potential which is negative with respect to the cathode of said transmission tube, and means for applying the direct current voltage output of said recti?er diode signal recti?er, means electrically associat~ ed with the?rst said means for preventing the diode anode from assuming a negative potential with respect to the transmission tube cathode, and additional means for applying the direct cur rent voltage output of said recti?er to the input 50 55 electrode of said transmission tube in a sense to increase said normal negative bias as signal am plitude increases. 5. In combination with a signal ampli?er of a 60 radio receiving tube, a diode recti?er for the out put of said signal ampli?er, means coupled to said recti?er for utilizing the modulation component of the recti?er output, means for deriving a direct current voltage from the recti?ed output of said recti?er, means for normally maintaining the 65 diode anode and cathode at a direct current po tential which is positive with respect to the oath ode of said ampli?er, and additional means for applying said direct current voltage output of the recti?er to the input electrodes of said ampli?er in a sense to decrease the gain of the ampli?er as the received signal amplitude increases. HAROLD O. PETERSON.