US2222759A - Voltage doubling signal rectifier circuit - Google Patents

Description

NOV. 26, 1940. D, G. BURN5|DE 2,222,759

VOLTAGE DOUBLING SIGNAL RECTIFIER CIRCUITS Filed May 18, 1934 2 sheets-sheet 1 1;- INVENTOR DON G. BURNSIDE BY/l/y//Mrvl/L. ATTORNEY Nov. 26, 1940. D. G. BURNSIDE 2.222,759

VOLTAGE DOUBLING SIGNAL RECTIFIER CIRCUITS Filed May 18, 1934 2 sheets-sheet 2 70 .N6/VAL $00365 AMC.

INVENTOR DON G. u

SIDE +250 BY ATTORNEY Patented Nov. 26, 1940 PATENT OFFICE VOLTAGE DOUBLING SIGNAL RECTIFIER CIRCUIT Don G. Burnside, East Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 18, 1934, SerialrNo. 726,210

6 Claims.

My present invention relates to signal rectilication networks, and more particularly to circuits for using tubes in voltage doubling detector and` amplifier circuits.

One of the main objects of my present invention is to provide circuit arrangements whereby multi-element tubes of two diodes and a triode, screen grid or pentode may be utilized to serve the `purposes of full wave voltage doubling demodulation, furnishing doubled automatic gain control voltage and of dernodulation frequency voltage amplification.

Another important object is to provide voltage doubling rectifier systems, which may have associated with them amplifier sections where desired, the tubes being employed in such demodulation systems 4essentially comprising a pair of independent diode units arranged to develop across a load resistor voltage components for audio network utilization, or gain control regulation.

Still other objects of the invention are to improve generally the eiliciency and simplicity of demodulation systems, and to particularly provide a demodulation system which is` not only reliable in operation, but readily constructed and assembled in a radio receiver.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims. Thev invention itself, however, both as to its organization and method of operation, will ibest be understood by reference to the following description taken in connection with the drawings, in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into eifect.

In the drawings:

Fig. 1 shows a circuit embodying the present invention,

Fig. 2 shows a modification,

Fig. 3 shows still another modification of the invention, and,

Fig. 4 is a diagrammatic showing of a circuit construction in accordance with applicants invention wherein detector voltage doubling is obtained together with audio frequency amplification.

Referring now to the accompanying drawings, wherein like reference characters in the different figures represent similar circuit elements, there is shown in Fig. 1 in purely schematic fashion a radio receiving system of a type including a source of signals, which may be the usual signal collector, and which signalcollector may be a grounded antenna circuit or a loop antenna, or even a signal transmission line feeding the receiving system. The source ofsignals feeds a network I which is denoted in Fig. 1 as a signal amplifier network. This network'l may be, in

the case of a superheterodyne receiver, the intermediate frequency ampliiier following the frequency changer stage, and the source of signals I' can then represent the tuned radio frequency amplifier and frequency changer circuits ahead of the intermediate frequency amplier. Where the receiver is of the tuned radio frequency type the network I may represent a plurality of cas caded tunable radio frequency amplifiers. In any case, the numeral 3 denotes a tube of the 25Z5 type, a tube well known to those skilled in the art.

'I'he network including tube 3 is the `signal rectifier, or demodulator, network, and its tuned nput circuit 4 is shown coupled to the output of4 amplier network l, as at M1.` The tube 3 briefly comprises a pair of indirectly heated diodes disposed in a single tube envelope, the diode `anode 5 being connected to the high Voltage side A of the tuned input circuit 4, the indirectly heated cathode 6, associated with the other diode anode l, being connected by lead 8 to the point A. The indirectly heated cathode 9, associated with the diode anode 5, is connected through a condenser C2 to the low alternating i voltage side B of the input circuit 4.

The diode anode I is connected to the ungrounded sideof condenser C2 through a path which includes the lead ID and condenser C1. The anode side of condenser C1 is connected to ground, it being noted that cathode 9 is also con` nected to ground, through a path which includes lead Il and the load resistorRi. The point intermediate condensers C1 and C2, to which the low alternating voltage side of circuit 4 is connected, is denoted by the reference letter T.

The direct current voltage component developed across load resistor R1 is used for automatic gain control of one or more tubes preceding the tube 3, and for the purposes of illustration the lead A. V. C. is to be understood as denoting the automatic volume control connection from the negative side of resistor R1 to lone or more of the grid circuits of the amplifier tubes preceding the signal rectifier stage. The A. V. C. lead includes the usual lter elements F for suppressing the pulsating current components that may normally be fed to the A. V. C. connection. The audio frequency voltage component developed across the load resistor may be transferred to a ACTI lzo

succeedingy audio frequency amplifier network through the tap I2 and audio coupling condenser I3. Of course, any well known type of reproducer would be employed subsequent to the audio ampliiier.

Fig. 1 shows the simplest form of a voltage doubler signal rectification network. It will be observed that the tube 3 and its associated circuits serve the purpose of full wave voltage doubling demodulation, and furnish doubled automatic gain control voltage. The process of rectication, or demodulation, involved in the network including tube 3 will now be explained. It

will be understood, in connection with the construction of tube 3, that the cathodes `9 and Ii arev physically independent of .each other, and only have in common a joint heater, or rather two k heater sections connected in series as shown in the drawings. k

It will also be observed that the anode 'l is connected `to the Acathode Si through a suitable load resistor so that inthe rectication process a direct voltage is built up across the load resistor due tothe carrier, or high frequency, voltage, and that 'Ia variationin this voltage occurs at the rate of modulation of the carrier. During the half 'cycle that the point A is positive, the rectifier unit 5, 9 conducts and charges condenser C2, the charge having polarity as indicated by the minus and plus signs adjacent the condenser electrodes.

During the negative half cycle the rectifier unit 7, d conducts and charges condenser Ci. In this case, also, the polarities created by the charging step are indicated. The two condensers being tector sensitivity and automatic volume control is concerned, equivalent to a single rectier unit coupled to an ampli-fier having a voltage gain of two.

`It may be found that when the tube 3 is of the 25235 type a certain amount of hum may develop. Employing a l2 volt heater for the heater ele- Vment I4 appreciably reduces such hum. To substantially minimize the hum a 6 volt heater I4 may be used, and it will be found that when'the filament is grounded through the movable contact of a potentiometer, and adjustment is made for minimum hum, the results are very good. The

circuit arrangement shown in Fig. 1 does not provide audio frequency voltage amplicatiom but this may be readily furnished by utilizing an ,amplier unit in conjunction with the tube 3.

An arrangement for providing full wave voltage doubling demodulation, doubled automatic gain control voltage and amplified audio frequency voltage is shown lin Fig. 2. In this circuit arrangement tube 3' again includes the two diode rectifier units 5, 9 and "1,6, and the -diode rectifier electrodes are connected to the condensers C1 and C2, as well as the load resistor R1, as in the case of Fig. 1. However, in order to provide sufficient audio gain, and without the use of another tube, an amplier section is .incorporated in the same tube envelope which contains the two rectiiier units, the cathode of one of the rectifier units serving to supply electrons for the ampliiier unit. Thus, the cathode 9 is shown arranged to supply electrons to a control grid I4 and a plate I5, the

'through the coupling condenser Cs.

electron stream to the grid Irl and plate I5 being independent of the electron stream to the diode anode 5.

Voltage doubling occurs in the circuit of Fig. 2 exactly as in the case or Fig. l. The doubled direct current voltage developed across load resistor R1 is applied to the grids of the preceding amplier tubes .through the lter F to provide automatic control of the gain. The audio variation in the rectified voltage across resistor Ri is carried to the grid I4 of the amplier section of tube S The resistor R2 is connected between ground and grid III', and functions as a suitable grid leak for the amplifier unit. Bias voltage for the grid i4 is provided by the plate current flow through resistor R3, the latter being connected between the cathode side of load resistor R1 and ground, a by-pass condenser Cs being connected in shunt with the bias resistor R3. The plate I5 is connected to a source of direct current voltage B1 through a resistor Ri, and a` coupling condenser C5 'functions-to transfer the amplified audio voltage toa succeeding audioV network; the latter may comprise addi` tional ampliiier stages and/or a reproducer of any well known type.

Should the normal amplifier unit bias be of the same magnitude as that of the radio frequency amplifier tubes preceding the rectier network, then the drop across bias resistor R3 may be used as the bias for the radio frequency amplifier tubes. In such case the radio amplier tube cathodes can be connected direct vto ground thereby eliminating one or ymore bias resistors and their bypass condensers. y

Merely by way of example, and not by way of limitation, it is pointed out that the following constants may be employed'for the circuit vshown in Fig. 2:

C1=C2=500 micro microfarads 06:1.0 microfarads R3 depends on 'bias required, and plate current of tube. f

Since in a tube of the type denoted by the reference numeral 3 in Fig. 2 one cathode is common to one rectier unit and to a triode unit, and one plate and the other cathode are connected together, a 'baseihaving six pins can be used when a grid cap is used, or a seven pin base would provide al1 the necessary terminals. Of course, the multi-function tube 3', which uses two diodes and a triode, may use a screen grid section or a pentode section in place of the triode section. Again, the amplifier section of tube 3 can be used for radio frequency amplification prior to thev full wave voltage doubling Ydemodulation function.

In receiving circuits using automatic volume control it is often desirable to provide a certain degree of delay action in the automatic gain' control network. Accordingly, in Fig. 3 there is shown a modification of the full wave voltage doubling signal rectiiication network, wherein delayed automatic volume control is accomplished. The multi-function tube in this case is of the 12A'7 type. This tube briefly comprises a pentode amplifier section anda diode rectifier unit disposed within a single tube envelope. The pentode section comprises ananode D2, a cathode 26, and three interposed grids. The grid G1 is disposed l involves the use of a pentode tube of the 57 type within the regumion grid G2 and the cathode zu.

The grid G3 is connected to the cathode 20. The diode rectifier unit of the tube comprises the anode D1 and the cathode 2|. For the purposes of the present application it is suiiicient to point out that the cathodes 20 and 2| utilize a single heater as in the 25Z5 type. Since the specific construction of the 12A7 type tube is not a part of the present invention, it is believed that this explanation of its physical construction is suiricient.

The circuit connections to the cathodes 2| and 20, as well as to the anodes D1 and D2 are precisely the same as in the case of Figs. 1 and 2. In other words, the cathode 20 and anode D2 function as a diode unit. For this reason the reference characters used in connection with the circuit elements in the demodulator input circuit of Figs. 1 and 2 are again employed. The rectification secured in a voltage doubling dernodulation network using a 12A7 tube is somewhat critically dependent on the presence of a positive voltage on the screen grid G2 of the pentode section of the tube. With the screen at zero potential, with respect to the cathode, rectified current through the load resistor R1 was found to be almost completely absent with moderate values of applied input voltage, whereas a positive voltage of even l or 2 volts permitted a considerable current to iiow.

The practicability of maintaining the screen grid G2 at zero potential until a fairly large carrier voltage was applied, and then making the screen positive, provides a means of furnishing delayed automatic volume control. The advantage of such a system is the abruptncss with which control voltage may be developed, and provides a characteristic that more nearly approaches what is referred to as the ideal automatic volume control curve. The specific manner of controlling the positive voltage on the screen grid G2 which is biased beyond plate current cut-01T. The delay action is mostly determined by the bias cutoi. The 57 type tube is chosen because it has a relatively sharp cut-olf, and gives a more precipitate increase in screen voltage of the screen G2, but it is to be clearly understood that any other tubes of suitable construction and characteristics may be employed in place of the 12A7 and 57 type tubes.

As has been stated, one diode unit D1, 2| is the regular rectifier unit and the other diode unit is the cathode to plate path in the pentode section of the rectifier tube. The positive screen voltage is the drop across the resistor R2, disposed in the grounded cathode circuit of the 57 type tube, when the carrier voltage applied to the control grid 30 through the condenser C'z exceeds its biasshown as the voltage E02. This bias voltage is developed across a portion of the bleeder circuit P, connected between the terminals +B' and -B, and is applied between ground and the grid 3D of the 57 type tube through the grid leak resistor R'a. It will be noted that the condenser C3 is connected to the point A of the signal input circuit 4 through a path which includes lead 34, the latter connecting additionally to cathode 2| and anode D2.

It is apparent that the bias E22 mainly determines the point at which gain control starts, the gain control voltage being a direct current voltage developed across the rectifier load resistor R1. In addition to the control the screen grid G2 of the 12A7 tube has on rectification,

there is some influence exerted by the grid G1 on the rectication process, although this latter control is less than the one due to the screen grid. The grid G1 is connected by lead 40 to a point on the bleeder P which is of a potential En less than the potential EQ2. It will be observed that the grid G1 is given a fixed negative bias, the selection of which depends to some extent on the delay bias chosen for the 57 tube. The effect of a suitable bias on the 12A7 tube is to permit a more abrupt increase in the rectified voltage just as the carrier reaches a value sufficient to cause the screen grid voltage of grid G2 to become positive.

Another effect of a negative bias on the 12A7 type tube is to prevent any current flow through the load resistor R1 except that due to signal. A xed bias of the order of l to 2 Volts is usually suitable for this purpose. So far as rectification is concerned, however, this-.bias would be higher than that indicated because of the usual requirements ofthe delay bias on the grid of the 57 type tube. In connection with the construction of the circuit of Fig. 3, the following circuit constants are given, it being clearly understood, however, that these constants are given merely by way of illustration and are not to be considered limiting.

R1 :0.5 mg. R2 :0.25 mg. R3 :1.0 mg.

E61 -4.5 Volts Ecz -45 volts In Fig. 4 is shown a modified circuit using the 12A7 type tube of Fig. 3 for full wave voltage doubling for A. V. C.; detection; and arnpliiied audio, To an extent the circuit is similar to that shown in Fig. 2. Its main point-of interest resides in the fact that the screen is maintained at a xed positive potential and used as the audio output electrode. and will be understood from the preceding eX- planations. Constants that may be used, although not limiting in nature, are:

C1 :50o uur' C10 =0.05 microfarads R10 :1.0 megohms R1=0.5 megohms R11 :0.1 vmegohms 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 modications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

l, In a radio receiver, the combination 'with a carrier wave amplier, of a tube provided with at least two diode units and an amplifying unit, said latter unit comprising the cathode of one of the diode units, an anode and a control electrode, an input circuit for said tube upon which the carrier wave output of said amplifier is impressed, said input circuit being connected between the cathode and anode of one of said diode units and including, in series, a carrier wave coupling circuit and a condenser, a second input The circuit is believed clear,

circuit forsaid tube upon which the carrier wave output of said amplifier is impressed, said second input circuit being connected between the cathode and anode of the other diode unit and including, in series,` the carrier wave coupling circuit and a second condenser, a load impedance connected between the anode of said other diode unit and the cathode of the first diode unit, an audio frequency input circuit connected between the control electrode of the amplifier unit and a point of said load impedance, means for biasing said control electrode to secure amplification of audio frequency Variations impressed thereon, an audio frequency output circuit connected to the anode of the amplifierunit, a direct current circuit including said load impedance, connected between the cathode of the first named diode unit Aand the carrier wave amplifier for automatically varying the gain of said carrier wave amplifier as a function of the rectified voltage developed across the load impedance.

2. In a radio receiver, the combination with a carrier wave amplifier of a tube provided with at least two, rectier units, the first thereof comprising an anode, a cathode and at least one control electrode, the second unit comprising an anode and a cathode, an input circuit for said tube upon which the carrier wave output of said amplifier is impressed, said input circuit being connected between the cathode and anode of said first unit and including, in series, a carrier wave coupling circuit and a condenser, a second input circuit for said tube upon which the carrier wave output of said amplifier is impressed, said second input circuit being connected between the cathode and anode of the second unit and including, in series, the carrier wave coupling circuit and a second condenser, a resistance element connected between the anode of the second named rectifier unit and the cathode of the first rectifier unit, a direct current circuit including said resistance element connected between the cathode of the first-named rectifier unit and the carrier wave amplifier for automatically Varying the gain of said carrier wave amplifier as a function of the rectified voltage developed across the resistor element, a second tube provided with an anode, a cathode and a signal grid, a connection between the anode and cathode of said second tube including a source of anode current and a resistor device in series, means for coupling the carrier wave amplifier to said signal grid to thereby impress a carrier wave voltage on said signal grid, means for biasing said last-named signal grid beyond anode-current cut-off, the bias voltage impressed on the signal grid having a value such that anode current starts to fiow through the resistor device when the carrier voltage applied to the grid is in excess of a predetermined value, means for applying a positive potential upon the control grid of the first rectifier unit with respect to the cathode thereof comprising a direct current path between the cathode and control grid of said first-named unit including the resistor device, whereby a positive potential is impressed upon the control electrode only when the anode current flows through said resistor device, said first-named tube becoming operative to Vary the gain of said carrier wave amplifier When the control electrode of said first unit is positive with respect to the cathode thereof.

3. In a radio receiver, the combination with a carrier wave amplifier of a tube provided with at lleast two rectifier units, an input circuit for the tube upon which the carrier wave output of said amplifier is impressed, said input circuit being connected between the cathode and anode of each of said rectifier units, each connection including respectively, a series condenser, the two condensers being connected in series between the `anode of one of the rectifier units and the cathode of the other thereof, a resistor element shunted across the two series condensers, a direct current connection including at least a part of said resistor element between said tube and the carrier wave amplifier for automatically varying the gain of said amplifier as a function of the rectified voltage developed across the resistor, means for maintaining said tube normally inoperative, a second tube provided with an input circuit and an output circuit, means for impressing carrier wave energy upon said input circuit, means connecting said output circuit to said firstnamed tube and means including said lastnamed means for rendering the first tube opera tive when the carrier wave voltage impressed upon the input circuit of the Second tube exceeds a predetermined value.

4. In a radio receiver, the combination with a carrier wave amplifier of a delayed 'automatic volume control circuitcomprising a grid controlled rectifier unit having input terminals and output terminals, means for impressing the carrier wave amplifier output across the input terminals of the rectifier unit, a load impedance across the output terminals of the rectifier unit, a direct current connection including the load impedance between the rectifier unit and the carrier wave amplifier for` automatically varying the gain of said amplifier Vas a function of the rectified Voltage developed across the load impedance, means for normally biasing the grid of the rectifier unit so as to maintain the rectifier unit inoperative and thereby prevent variations in the gain of said amplifier, an electronic tube having an input circuit and an output circuit, means for connecting the grid of the rectifier unit to said output circuit, means for transferring carrier wave energy to said input circuit, said electronic tube being biased beyond anodecurrent cut-off and means acting when the potential of the carrier wave impressed upon the input circuit of the electronic tube exceeds the bias potential applied to the tube for acting upon the rectifier unit to render said unit operative to control the gain ofthe carrier wave amplifier.

5. In a radio receiver, the combination with a carrier wave amplifier of a tube provided with at least two rectifier units each thereof being provided with an anode and a cathode, and an amplifying unit, said amplifying unit comprising the cathode of one of the rectifier units, a signal grid and an auxiliarygrid, said signal grid and auxiliary grid being interposed between the cathode and anode of the last-named rectifier unit, said auxiliary grid being utilized as the anode of the amplifying unit, an input circuit for the tube upon which the carrier wave output of the amplifier is impressed, said input kcircuit being connected between the cathode and anode of said last-named rectifier unit and including in series, a carrier wave coupling circuit and a condenser, a second input circuit for said tube upon which the carrier wave output of said ampiner is impressed, said second input circuit being connected between the cathode and anode of the other rectifier unit and including in series, the carrier Wave coupling circuit, a second condenser and a load impedance, an audio frequency output circuit connected to said auxiliary grid electrode, means for connecting a point of said load impedance to the signal grid of said amplifier unit, means for biasing said signal grid to secure amplication of audio frequency variations impressed thereon, a direct current circuit, including the load impedance, connected between a cathode of the first-named rectier unit and the carrier wave amplifier for automatically varying the gain of the carrier Wave amplier as a function of the rectified voltage developed across the load impedance.

6. In a radio receiver, the combination with a carrier Wave amplifier of a delayed automatic volume control circuit comprising a grid controlled rectifier having input terminals and output terminals, means for impressing at least a part of the carrier wave amplifier output across the input terminals of the rectifier, a load impedance across the output terminals of the rectiiier, a direct current connection including' the load impedance between the rectifier and the carrier Wave amplifier for automatically varying the gain of said amplifier as a function of the rectified voltage developed across the load irnpedance, means for normally biasing the grid of the rectier unit to maintain the rectifier unit inoperative and thereby prevent variations in the gain of the amplifier when the carrier Wave amplifier output voltage is below a predetermined value and means for changing the biasing on said grid so as to render the recter unit operative when the said output voltage exceeds the predetermined value to thereby cause the gain of said amplifier to be Varied as a function of the rectified output of the rectifier.

DONh G. BURNSIDE.

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