US2048100A - Combined detector-automatic volume control circuits - Google Patents

Description

July 21, 1936- I D. G. BURNSI,DE

COMBINED DETECTOR AUTOMATIC VOLUME CONTROL CIRCUITS Filed NOV. 25, 1952 DON G. BURNSIDE lfg/wv ATTORN EY- Patented July 21, 1936 COMBINED DETECTOR-AUTOMATIC VOLUME CONTROL CIRCUITS Don 'G. Burnside, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application November 25, 1932, Serial No. 644,149

' 11 Claims. (01. 250-20) My present invention relates to improvements in combined detector-automatic volume control circuits, and more particularly to circuits of this typev .whichutilize tubes of the duplex-diode triode type. V

. There is disclosed by T. M. Shrader in application Serial. No. 622,140, filed July 12, 1932, a multiple duty electron discharge tube known as a duplex diode-triode, and designated numerically as of the 55 type. In the said application there have also been disclosed various circuit arrangements for utilizing such a tube as a combined detector-automatic volume control tube; the said circuit arrangements are claimed in Shrader divisional application Serial No. 686,718,

filed August 25, 1933. Briefly, it may be stated that such a tube is capable of simultaneous use as a detector or demodulator, an amplifier, and also'urce of automatic volume control potential. In'generaLsuch a tube comprises one, or more.

. diodev sections and a triodesection, all disposed within a single tube envelope.

Summarizing the disclosures of the aforementionedapplicationait can be stated that there is provided a single electron discharge device which is mechanically. a unitary device, but, functionally, is an amplifying triode, and 2; rectifier having two anodes which are electrically independent of each other and of the amplifier. Such a device has many applications, and has very great flexibility for use with many different kinds, of. circuits because of the electrical independence or the diodes and the amplifier. The electrodes of the device 'are enclosed in a single envelope, and are combined in a single mount having a common cathode, with the grid and plate of the amplifier surrounding the cathode near one end, and the rectifier anodes mounted near the other end on independent leads.

' One of the main objects of the present invention is to provide a circuit including half wave diode rectification for detection and automatic volume control, the rectification further furnishing the self-bias of the grid of the triode section of 'atube of the duplex diode-triode type.

And still another object of the present invention is to provide a circuit and tube combination, the tube being of the duplex diode-triode type, embodying delayed automatic volume control in order that the ordinary noises present in the receiver may not be reproduced in the absence of the carrier.

And still other objects of the invention are'to improve generally the simplicity and efiiciency of receivers employing combined detector-auto-' matic volume control-audio frequency amplifier stages, and to particularly provide a receiver of this kind which is not only reliable in operation, but economically manufactured and assembled.

The novel features which I believe to. be characteristic of my invention are set forth in particularity 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 20 connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect. 1 1

In the drawing,

Fig. 1 diagrammatically showsa superheterodyne receiver employing a multiple duty tube embodying one form of the'present invention;

Fig. 2 shows a portion of the receiver in Fig. 1 embodying a modified form of the invention; and,

Fig. 3 shows a further modification of the invention.

Referring now to the accompanying drawing wherein like reference characters in the different figures designate similar circuit elements, Fig. 1 diagrammatically showsa'receiver of the superheterodyne type, wherein the second detector stage includes a circuit and tube combination employing the present invention; Thus, in Fig. 1, there is shown preceding the multiple duty tube I the conventional superheterodyne receiver stages. As is well known in the art, such a receiver usually embodies a radio frequency amplifier which is tunable, a local oscillator, a first detector and an intermediate frequency amplifier of one, or more, stages. The output of the intermediate frequency amplifier is. impressed upon the, second detector, and the audio frequency output of the second detector is supplied to an audio frequency amplifier, and finally a reproducer.

Thetube I is of the 55 type, that is a duplex diode-triode tube, and includes a plurality of electrodes arrangedin the manner described in the aforementioned Shrader application Serial No. 622,140. 7 Such a tube includes a pair of diode sections and a triode section which are independent of each other. The triode section includes an 0 electron emission electrode 2, such as a unipotential cathode. This cathode preferably comprises a sleeve extending lengthwise of the tube envelope, and contains a heater 3 which is connected to the usual alternating current heating source. The control grid 4 of the triode section is disposed between the cathode 2 andthe main anode 5, and in actual construction these three electrodes are co-axial cylinders. The cathode sleeve is longerthan the triode assembly; it projects beyond the grid and main anode, and this projecting portion of the cathode sleeve is the cathode of the rectifier or double diode. This has been diagrammatically represented in Fig. 1. V

Thus, the diode anode D1'is disposed adjacent one portion of the cathode surface, and the other diode anode D2 is disposed adjacent another portion ofthe cathode surface. .Both of thesecathode portions areindependent of the cathode surface whichfurnishes the electron stream which flows through the grid 4150 the main anode 5. The tube I may be said to embody a cathode which is common to both the triode and the. two diode anodes, but the diode anodes are positioned outside'the electron. stream to .the triode grid and anode. In actual construction, the diode anodes D1 and D2 are disposed adjacent the aforementionedprojecting end of the cathode sleeve, and

' are electrically independent of each other-and of the triode section.

These rectifier anodes may be very much smallerfthan: .those of the rectifying tubes generally used in receiving sets, since :very small currents 'Shrader disclosure is considered a portion of the develop sufiicient rectified voltage to give the de-. siredresults; The aforegoing description of the tube l. is believed suificient for the purposes of the present application-inasmuch as, as statedfheretofore, the above Shrader application Serial No. 622,140 describes the said tube in great detail, and it is to be clearly understood that this said present. disclosure. I

The signal voltage E0, which signal voltage in Fig. 1 isthe amplified output of. the intermediate frequencyamplifier, is shown supplied from the.

carrieryoltageEc is applied to thestransformer M1. 1. i Q U R.adiofrequency components are by-passed by the condenser C1, while the filter R2*C2 permits the passage of-the direct. current voltageto the path designatedA. :V. C. (meaning automatic volume control) without a substantial amount of. was frequency voltage. The audio frequency component developed across the resistor R1 is supplied to thegrid 4 of the triode section of" tube l, in proportion" to the voltage E0 and to its degree of modulation] This audio frequency component is amplified, and repeated 1-11 the cathode-anode circuit of the triode section of tube l-. Theamplified audio frequency component flowing through the resistance in the circuit of anode 5, which resistor R is in series with the +3 terminal of .the anode potential sourcejproducesfa:voltage drop across the resistor R which is supplied to the audio frequency amplifier of the receiver.

The grid 4 is connected to-the negative side of the resistor R1, and this connection is made through a lead 1 thereto. Preferably, the lead I is terminated by an adjustable tap8. The tap functions as a manual volume control to vary the intensity of audio frequency component delivered Rectification. for detector .and automatic volume control purposes occurs between the diode plates and the cathode under the influenceof a signal modulated alternating voltage. The rectified current flowing through the resistor RiJnot only produces the audio frequency signal for the receiver, but further furnishes the automatic.

volume control bias which is supplied tothe radio 1 frequency amplifier the firstdetector and intermediate frequency amplifier stages through the network including the filterR2-0z and the lead 9. It is not necessaryto describe the. manner in which the negative bias supplied through the automatic volume control network is utilized for; automatically. controlling the gain'of each of 9 the controlled stages, it beingbelieved well known to those skilledin the art how this is iaccomplished.

It is only necessary to point out that thisiis usually arranged so that thesignal intensity leveldelivered to the transformer M1 is'maintained substantially uniformras long as signal is being received. r r

. .In Fig. 2 the signal voltage E0 is applied directlyonly to the diode plate D1 withthe result that the signal is rectified, and applied, as in Fig. 1, tothe grid of the triode section by means of. coupling condenser C3. A desired amount of fixed bias may be applied to the triode gridby means of the source of negative; potential E3. Thediode anode D1 is eectrostatically, coupled to the diode anode D2 by means of condenser C2 whereby the incoming signal is additionally supplied to the second diode circuit. This signal, when rectified, flows. through the resistor R z, and produces a negative voltage at the righthand'end thereof; the negative side of theresistorR'a being connected by a lead 9 to the automatic volume con- By. biasing the anodeDi negatively with respectv to the cathode, the bias source being indicated conventionally as E1, there is no rectification of the signal until it attains a desired predetermined. threshold value. p This eliminates most of. the ordinary noises present in the receiver which are not desired to be reproduced in the absence of a signal carrier. The source ofpotential E2; is so arranged as to bias the plate D2 negatively-by a predetermined, amount; this amount necessitat ing a, peak value of signal Eo. greater than the value of the bias furnished'by source E2 before volume control voltage action. can start. This produces delayed automatic volume control action. I 9

It will, therefore, be seen that in Fig. 2 there is shown a method or using .two rectifier anode plates separately, one being; employed for de--v modulation andthe otherfor automatic volume; control. The signal is supplied directlytoflthe. plate D1. 7 Duringthe positive half cyclerectified current flows through'the resistor R; by virtue of rectification. A voltage drop occurs across the resistor R1, the latter being by-passed by condenser C1 to afford a low impedance path for the radio or intermediate frequencies. The audio component of rectified voltage across resistor R1 is'impressed on the control grid of tube I through the coupling condenser C3.

If desired, the direct connection shown in Fig. 1 may be utilized. By biasing the plate D1 negatively with respect to the cathode, the more or less constant tube and circuit noise voltage may be eliminated or reduced. The bias value of source E1 may be such that it is just above the noise level on the demodulator plate D1- This, then, serves as a noise suppressor device which functions to render the receiver demodulator inoperative until a predetermined ratio of signal to noise voltage is exceeded.

The capacitor C2 is of such a magnitude that it passes to the rectifier anode D2 the signal on plate D1 with but little attenuation. The section including plate D2 thus becomes an independent rectifier so far as direct current is concerned. The resistor R2, being the external resistor for this rectifier, has current flowing through it when the plate D2 is positive, This direct current component of rectified voltage across resistor R2 is employed for automatic volume control. Thegeneration of automatic volume control voltage may be delayed to any desired extent by application of the negative voltage from source E2 to the plate D2. In this event the peak value of signal must exceed the negative bias on plate D2 before any volume control action can be initiated.

The source E2, therefore, represents a device for securing delayed automatic volume control, and is' a device which functions independently of the noise suppressor device which governs the point at which demodulation can commence. Instead of a resistor B being disposed in the circuit of the main anode of tube I, there is shown an auto-transformer L, the drop across which is employed for audio frequency amplification.

Of course, this auto-transformer may also be the primary of a transformer of the well known type.

Another modification of the invention is shown in Fig. 3 wherein the signal transmitted through the transformer M1, this signal either being at radio or intermediate frequency, is amplified prior to rectification, which is contrary to the procedure disclosed in Figs. 1 and 2. The'high frequency voltage, amplified by the triode section of tube I, is impressed on the rectifier anodes D1 and D2 by means of the capacitor Cfi, which capacitor is connected between the main anode 5 and the diode anodes D1 and D2. The capacitor U1 is of such a size that while its impedance to the high frequency currents is low, it has a relatively high impedance to audio frequencies. Of course, in place of U1 there can be used any other type coupling as an rj. or if. transformer. A form of shunt feed for the triode plate 5 is used, the radio frequency choke L1 preventing loss of high frequency voltage, and, at the same time, permitting direct current voltage to be supplied to the plate.

The amplified radio frequency or intermediate frequency voltage is impressed on plates D1 and D2 together, or separately in case independent use of each is desired; this causes rectification to occur. The .resulting potential drop across resistor R'1 is used, in the case of the direct componentof rectified voltage, for automatic volume control through a suitable filter, and in the case of audio component of the rectie fied voltage, the potential drop across .resistor R1 may be used for further voltage amplification, or for power amplification. The automatic volume control voltage may be taken from the point indicated, that is at the negative end of the resistor R1, and the audio voltage E1 may be taken from across the resistor Ri or any desired part thereof.

It will, therefore, be seen that the circuits of tube l in Fig. 3 are so arranged that the incoming signal is applied directly between the cathode and grid of the triode section, the source E4 furnishing negative grid bias for the grid of tube I when this is desired. The amplified voltage from the main plate circuit is delivered through the condenser C1 to the diode plates D1 and D2 in parallel, the direct current flowing through the resistor R'1 under the influence of the signal voltage producing a difference of potential. The direct current component of the potential drop across R'1 is led ofi to the automatic volume control circuit, as employed above, and the audio component may be taken off across the resistor R'1 in the usual manner.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

l. The combination with an electron discharge tube comprising an envelope enclosing an electron discharge section including at least a cathode, grid and plate, and a rectifier having two independent anodes, of an oscillatory circuit having one side thereof connected for radio frequencies to both said anodes, and its other side connected to said cathode, a resistor disposed in said other side, a connection between the grid of said tube and a point of said resistor, a fixed bias source connected between said grid and said cathode, an automatic volume control path connected to one of said anodes, and a volume control bias resistor connected between said path and said cathode.

2. The combination with an electron discharge tube comprising an envelope enclosing an electron discharge section including at least a cathode, grid and plate, and a rectifier having two independent anodes, of an oscillatory circuit having one side thereof connected for radio frequencies to both said anodes, and its other side connected to said cathode, a resistor disposed in said other side, a connection between the grid of said tube and a point of said resistor, a fixed bias source connected between said grid and said cathode, an automatic volume-control path connected to one of said anodes, a volume control bias resistor connected between said path and said cathode, and means connected to theother of said anodes for preventing demodulation whenever little or no signal carrier is impressed on said oscillatory circuit.

3. The combination with an electron discharge tube comprising an envelope enclosingan electron discharge section including at least a cathode;

grid and plate, and a rectifier having two indeside, a connection betweenthe grid .of said .tube if latory circuit attains a predetermined threshold value.

4: The combination with an electron discharge tube comprising an envelope enclosing an electron discharge section including at least a cathode, grid-and plate, and a rectifier having twoindependent anodes, 01 an oscillatory circuit having one side thereof connected for radio frequenciesto both said anodes, and its other side connected to said cathode, a resistor disposed in saidother side, a connection between the grid of said tube anda point of said resistor, a fixed bias source connected between saidgrid and said cathode, an automatic volume control path connected to one of said'anodes, a volume control bias resistor connected'between said path and said cathode,

meansconnected to the other of said anodes for preventing demodulation whenever little or'no signal carrier is impressed on said oscillatory circuit, and means'connected to'said'volume control path and anode for delaying the automatic volume control action until the signal carrier impressed on said oscillatory circuit attains a predetermined threshold value. V a t In combination with a'source of signal modulated radio frequencyo carrier energy, a multiple function tube including a cathode, a signal grid, main anode and a diode anode, a signal input circuit coupling said source to saiddiode anode and cathode, an impedance in said input circuit across which the said carrier energy develops an audio frequency potential, a connection from said grid to said impedance, an audio frequency networkcoupled to said main anode, signal level controlmeans independent of the circuit including said impedanceresponsive to signals impressed on said input circuit, for producing solely a direct current potential varying in magnitude with sig- I nal amplitude, and'means connected to said input circuit for maintaining the diode anode negative 'with. respect to the cathode until the impressed 50;

carrierenergy increases above aipredetermined intensity level.

6, In combination with a source of signal modulated radioofrequency carrier energy, a multiple function tube including a cathode, a signal grid, main anode and a diode anode, a signal input circuit coupling said source to said diode anode and cathode, a diode rectifier network coupled to said input circuit, said network including an impedance, and an automatic gain control-connection connected to a point'on said impedance,

an impedance in said input circuit across which the said carrier energy develops an audio frequency potential, a connection from said grid to said last impedance, an audio frequency network tol'said input circuit for maintaining the diode anode negative with respect to the cathode until the impressed carrier energy predetermined intensity level.

7;;In a radio receiver, a multiple duty tube provided with at least a cathode, a signal grid, a main anode,"and two diode anodes, a signal input circuit connected between one of the diode anodes and said cathode, said other diode anode being connected to said input circuit, a resistor in said increases above' a inputcircuit, a second'resistor connected between V the cathode and the said other diode anode, a direct current connection to a point of negative potential-'on-said second resistor, a connection between said grid and a point on "saidfirst resistor, a load circuit; connected to said main anode, and :means for biasing said diode anodes V negatively with respect to said cathode, 7

8. In a radio receiver, a multiple duty'tube provided with at least a cathode, a signal grid, a' main anode, and two diode anodes, a signal input circuit connected between one of the diode anodes and said cathode, said other diode anode being connectedto said input circuit, a resistor in said input circuit, a secondresistor connected between the cathode and the said other diode anoda a direct current connection to a point" of negative potential on said second resistor, a connection between said grid'and a pointon said first reanodes and said cathode, said other diode anode n V being connected to'saidinput circuit, a resistor in said input circuit, a second resistor connected between the cathode and the said other diode anode, a direct point of negative potential on said second resistor, a connection betweensaid grid and a point on said first resistor; a load circuit connected to said main anode, means for biasing the'gridi'negatively with respect to said'cathode, and means for biasing said diode anodes negatively with respect to saidcathode. v I

10. In a radio receiver, a multiple duty tube provided withat least a cathode, a signal grid, a main anode, andtwo diode anodes, said diode anodes being outside the electron stream to said grid and main anode, a signal input circuit conF I nected between one of the diode anodes and said current connection to a circuit connected to said main anode, and means 7 for biasing saiddiode anodes negatively with respect to said cathode;

11. In combination with an electron discharge tube of a type including at least a cathode and two anodes and said cathode providing independent electron streams to said anodes, a source of modulated" radiofrequeney carrier energy, can input circuit, tuned to the carrier frequency, con-f nected between said cathode andone of the anodes, an impedance in said circuit with said input circuit whereby a signal detector network is provided a second impedance in circuit with said cathode and the second anode and providing a carrierenergy rectifier network, an automatic gain control connection to a point'on said second impedance, means operatively associated with the detector network for preventing detection until a predetermined'carrier amplitude is attained; and means operatively associated with the recti'- fier network for delaying the gain control action amplitude is attained.

until a desired carrier DON G. BURN SIDE'.

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