US2106207A

US2106207A - Automatic volume control system

Info

Publication number: US2106207A
Application number: US33118A
Authority: US
Inventors: Crossley Alfred; Herbert E Meinema
Original assignee: Johnson Laboratories Inc
Current assignee: Johnson Laboratories Inc
Priority date: 1935-07-25
Filing date: 1935-07-25
Publication date: 1938-01-25
Anticipated expiration: 1955-01-25

Description

Jan. 25, 193s,-

all

ACROSSLEY i-:r AL' AUTOMr-'IICl VOLME CONTROL SYSTEM Filed July 25,' 1935 Qns:

f ,du-"PED Cpo SL EEBBEQETE E/NEWA,

. ATTORNEY.

30 modulator substantially constant in'spite of wide requirements are objectionable in any receiver; 30

45 eral different sets of conditions; and

' 5o Vacuum-tube amplifiers of the type herein con- The simplest forms of automatic amplication 50 Patented Jan. 25V, 1938 I I l I UNITED STATES lPATENTA ol-Fica 2.106.207 i AU'roMA'rIc vomlun CONTROL SYSTEM Alfred .Crossley and Herbert E. Meinema, Chicago,

Illa assignors to Johnson Laboratories, Inc., Chicago, Ill., a lcorporation of Illinois a Application July z5, 1935, serlal No. 33,113

8 claims. (cl. 25o- 20) This invention relates to improvements in vachigh-frequency signals for the transmission of uum-tube amplifying systems. More specifically, intelligence.v Although the-arrangements of the this invention relates to improvements ,in the present invention are applicable to vacuum-tube means for automatically regulating the ampliamplifiers-of all types, they are Iof especial advancation of a vacuum-tube amplifying system. 'tage in the high-frequency amplifiers of radio re- 5. An object of thisinvention is to provide animceivers. In this case, it is usually desirable that proved method of amplification control which au-v the output signal level remain substantially contomatically maintains the output level of a vacstant in spite of wide variations in the input signalv uum-tube amplifier substantially .constant in voltage due to fading or to the. Widely different 10 spite of wide variations in the input voltage. signal strengths whichare encountered in tuning 10 Another object of the present invention is to from one signal to another from a diierent source. provide a system of automatic amplification con- The usual radio receiver consists of a high-fretrol which is responsive to relatively small changes quencyamplifying system, a demodulator, and a in the voltage at tire output of` a vacuum-tube low-frequency amplifier. Since the demodulator 15 amplier. performs most satisfactorily within a relatively A further object of this invention is to provide narrow range of signal levels, it is the usual pracmeans whereby the control of amplification which tice toregulate the amplification of the highis automatically applied to a vacuum-tube amfrequency amplifying system either manually or pliiler is'self-increasing. automatically, in such a'way as to maintain the Still another object of the present invention is signal at the demodulator substantially constant to provide an amplified control voltage for the despite large variations in the strength of the inautomatic regulation of the amplification of a coming signal. Ifthis operation is performed yvacuum-tubo amplifier, without the use of addimanually, constant attention on the part of the tional vacuum tubes other than a demodulator. user is vrequired to compensate for the relatively An additional object of this invention is to rapid changes in the incoming signal strengtln 25 provide an automatic amplification control system Furthermore, whenever the receiver is adjusted to which may be satisfactorily employed in conjuncreceive a different station the manual amplication with the high-frequency amplifier of a radio tion control must be re-adjusted to produce the receiver, to maintain the signal level at the dedesired output level from the new signal. These variations in the .input signal voltage. and are especially disadvantageous in the case of Still a further object of the present invention is 'receivers intended for mobile use, as in automoto provide an automatic amplification control sysbiles or motor boats. tem which has a desirable input vs. output char- Various arrangements have been employed in acteristic, but which does not prevent the full the past to Aautomatically vary the amplification utilization of the amplification of a vacuum-tube of the high-frequency amplifying system of a. amplifying system. radio receiver in accordance with changes in the Although a discussion of the principles underinput signal level. These arrangements are lying our invention is necessary to a full underusually operated by rectifying a portion of thestanding thereof, certain portions of this specificaoutput voltage, and applying the rectified volt-T40 tion will be bestunderstood when taken in con- 'age to a control electrode of one ormore of the ynection with the drawing, in which high-frequency amplifying vacuum tubes, there Fig. 1 is a graph showing the usual automatic by regulating the amplification of the system in amplification control characteristics under sevapproximate accordance with the amplitude of n the input signal. In somel cases, the control is Fig. 2 is a schematic wiring diagram of a porapplied also t a-low-frequency amplifying vaction of a radio receiving apparatus incorporating uum tube, the aim being to supplement the reguour invention and serving as an illustrative emlation of amplification which is obtained in the bodiment thereof. l high-frequency portion of the receiver.

templated are used in both low-frequency and control systems decrease the amplification as soon high-frequency communication systems. Lowas any output signal is present, the degree of frequency amplifiers are commonly employed in reduction increasing as the output signal increases l telephone systems. High-frequency ampliers -in amplitude. These arrangements prevent the are widely used in systems employing modulated full utilization of the high-frequency ampliflca- 55 level.

tion of the receiver, since the amplification is reduced by any signal at the output. `Furthermore, the reduction in amplification does not keep pace with the increasing input signal voltage, with the result that the output level inbe introduced by suitable means. In 'either case,

delaying the action of the 'automatic control permits the full sensitivity of the receiver to be utilized.

The problem of decreasing the amplification at a sufficiently high rate to keep pace with an increasing input signal is especially acute in the case of small receivers having only a limited number of high-frequency amplifying vacuum tubes to which the control voltage may be applied. The number of stages which, may be controlled is further limited by the fact that a vacuum tube which drives a' diode rectifier should .preferably be operated at a fixed bias voltage.

With only a limited number of vacuum tubes to be controlled, therefore, the only alternative is to amplify tlie output voltage from the rectifier before applying it to the control electrodes of one or more high-frequency amplifying vacuum tubes.

Amplification of the control voltage has, prior to the present invention, required either an additional vacuum tube or a substantial sacrifice in the effective plate potential available for the controlled amplifying Y vacuum tubes, or both. The arrangements of the present invention, however, provide for the amplification of the control voltage without the necessity for an additional vacuum tube and without an appreciable sacrifice in effective plate potential on the controlled amplifying vacuum tubes. The advantage of such an arrangement is obvious in any receiver, and this is especially the case in receivers intended fo'r mobile service, where extreme compactness, wide-range automatic amplification control and economical operation are essential features of a satisfactory receiver. Furthermore, the arrangement of the present invention includes provision for obtaining a desirable delayed operation of the automatic amplification control, permitting the full sensitivity of the receiver to be efficiently utilized.

'I'he performance characteristics of various forms of automatic amplification control systems are shown graphically in Fig. 1. Curve A represents the ideal form, the output rising rapidly to the normal level and thence remaining constant atthis level. This characteristic is not attained in any simple arrangement. Curve B shows the performance of a simple control system in which a portion of the output signal is rectified and used to control the amplification of one or more preceding amplifying tubes. is required to produce normal outputand normal output is reached very graduallyas the inputincreases. Curve C represents the performance of a system similar to that of curve B, except that a delay effect has been introduced to prevent the automatic controi-v from4 operating i until the. output almost reaches its normal level. From this.

A very large input-epoint on, however, the output increases appreciably as the input increases. Curve D is the charaeteristic of a system according to the presentl invention, 'in which provision Vis made for both delaying and amplifying the control voltage which is applied to the amplifying vacuum tubes. In this case, the outputv soon reaches its normal level, and is closely maintained at this level as the input increases many times. closely approaches the ideal curve, indicating that the performance of the systemof the present invention is very satisfactory.

Although the arrangements of the present invention may be applied to various types of amplifying systems, the embodiment shown in Fig. 2 as an illustrative example consists of a threestage high-frequency amplifier followed by a diode rectifier. 'I'his type of amplifier is commonly employed in radio receivers. The diode rectifier may be used simultaneously as the control rectifier and as the signal detector or demodulator, or a separate rectifier may be employed as the demodulator. Both forms are within the scope of the present invention.

Referring to Fig. 2, high-frequency amplifying vacuum tubes I, 2 and 3, respectively, are cou- -pled in cascade by means of transformers 4, 5

and 6. Each transformer secondary is tuned to `the signal frequency by variation of a capacitor 1, or by variation of the effective inductance of the secondary itself. By-pass capacitors 8 furnish a low-impedance path for all high-frequency currents. Amplifying vacuum tube 3 has in its plate. circuit, inductor 9 and resistor I0, Aand its plate 30 is coupled to the anode II of rectifier vacuum tube I2 by blocking capacitor I3. Diode load resistor I4 is connected between anode i II and the junction of

resistors

23 and 24. The

cathode 21 of vacuum,tube 3 is connected to ground through

resistors

23 and 24. The directcurrent grid'return of vacuum tube 3 is connected to the junction of resistors vII and I8. 'I'he input signal to the amplifier is applied to Vprimary 26 of coupling transformer 4.

Vacuum tube I2 is a duplex diode, and includes a second diode anode 33 which in connection with cathode I5 is employed as the demodulator, the audio-frequency voltage being developed across resistor 34, connected betweendiode anode 33 and cathode I5. The amplified signal is fed to diode anode 33, through blocking capacitor 32.

When no input signal is present, an initial bias voltage for vacuum tubes I, 2 and 3 is developed across resistor 23. The values of resistors 2| and 22 are so chosen that the cathode 28 of vac-* uum tube 2 has the same potential relative to ground as the cathode 25 of vacuum tube I. In the absence of a signal, there is no appreciable voltage across resistor i4.

When a signal is applied to. primary 2S and amplified by vacuum tubes I, 2 and 3, and it exceeds the negative delay voltage on the diode anode II due to the voltage drop across resistor This curve 23, it will be rectified by vacuum l voltage appears across resistor Il.

tube n. as.

soon as rectification takes place, a direct-current This voltage adds to the initial bias on vacuum tubes I, 2-and l, thereby tending to reduce their mutual con-' ductance and hence their amplication.- A dey vf' creasein voltage drop across'resistor 23 occurs when the platel currents of vacuum tubes I and I. 3 decrease due to the increasing negative grid ylo uum tubes.

I' ase bias which is being applied to these vac- 'Ihis change in the voltage' drop across resistor 23 decreases the initial bias voltwhich is applied to'the grids yof vacuum tubes .I, 2 and V3, but simultaneously the delay voltage on diode anode II is decreased and permits the development of a larger control voltage y amplification of the system.

' however, the left-hand terminal of resistor becomes less positive with respect to ground.

Since the cathode 28 of vacuum tube 2 is at a substantially fixed positive across resistor Il. The nt result, if this were the only .means for automaticallyy regulating the would be a perfomance characteristic substantially like that represented by curve C of Fig. l.

As the voltage across resistor 2l decreases, I4

potential relative to Y ground, the effective negative' bias on grid 3| of vacuum vtube 2'increases. This increase is in addition 'to the bias voltage developed across diode load resistor Il. These two arrangements .combine to produce a very desirable self-increase in the overall' degree of amplification control, so'that the performance of the system is similar to that represented by curve D of Fig. l.

, derstood by noting that, in effect, vacuum tube I "featureis especially y Y mobileservice, where great variation in the fieldl The operation of the system willbe better unacts as a direct-current ampliiier.

Resistors

23 and 24 are in the direct-current plate circuit of vacuum tubes I and 3, and any change in the direct-current voltage ongrlds 29- changes they.

strengths of the signals is commonly encountered. l

It will be understood that vacuum tube I2 may l' be replaced by any other suitable type of recti- `er, asfor example a copper-oxide rectifier. In alpreferred embodiment, inductor 9 is resonantv at a frequency approximately midway between the extreme vfrequencies to which the system may `be tuned, and its resonance characteristic is understood,l however,

without departing from 'increased control voltage being applied to one broadened by means of resistor III. It will be meansymay be employed for coupling amplifying vacuum tube 3 to rectifier I2. The arrangements of the present invention may be applied to amplifiers having more or less than three stages the scope thereof, the

or more amplifying vacuum tubes, some or all of which may be .the intermediate-frequency amplifiers in a superheterodyne type of receiving apparatus; and the increased control voltage may also be applied to tubes which are subsequent to the demodulator, within the scope of this inven- I tion.

.be understood. however,

. of said first vacuum vacuum tube acts additionally as a'direct-current that any other suitable" Athe cathode of said third tube when no according -to` Fig. .2, the following components and constants will be found satisfactory. It will that any lof these values may be altered, and theyare not to be taken as in any way' limiting the scope of the present invention.

Reference numeral Type or value .Type78 Typ@ 78 TypeB? (pentode portion) Type 6B7 (diode portion) 0.1 microiarad 0. 4 miilihenry 5000 ohms 200 micromcrofarnds i. 0 megohm 0. l-megohm l. 0 megohm 0. 0l microiarud 750 ohms 25,000 ohms 750 ohms 750 ohms used in the arrangements shown in Fig. 2 being I used for any other desired purpose, as for example as a first stage of low-frequency ampliflcation.

Having thus described our invention, what we claim is:

1. In a ra'dio receive a multi-stage amplifier including plural amplifying vacuum tubes, a first means for automatic control of the amplification of a first and ajsecond of said vacuum tubes, and a second `means for controlling the amplification of said secondvacuum tube, said second means including plural resistors inthe cathode circuit tube whereby 'said first amplifier to increase the degree oiv control exerted upon said second vacuum tube by said first -control means.

f 42. In a multi-stag vacuum-tube amplifier, means for automatic amplification control including a diode rectifier coupled to the output of said amplierand having/a direct-current connection from its negative output terminal to a' control electrode of at least a first and a'second vacuum tube of said amplifier, means for successively delaying and increasing the effect of said automatic amplication control. including Aa, connection between the .cathode of said first vacuum tube and the cathode of a third vacuum tub'e; a connection between the cathode of Vsaid diode rectifier and the cathode of said third vacuum tube; a connection includinga first and a second resistor vbetween vacuum tube and ground; Aa connection between the junction of said first and second`resistors`and the positive terminal of a third resistor in the output circuit of said diode rectifier; and means for maintaining the cathode of said second vacuum tube at substantially the same potential relative to ground as that of the cathode' of said rst vacuum input voltage is applied to said amplifier..

coy

high-frequency vacuum-tube amplifier and a diode detector-rectifier, means for automatically regulating the amplification of said amplifier in accordance with changes in the direct-current output of said diode detector-rectier, said means including a direct-current connection between the anode of said diode detectorrectifier andA a control electrode of at least a first and asecond vacuum tube of said amplifier; a connection between the cathode of said first vacuum tube and the cathode of a third vacuum tube; a connection includinga first and a second resistor between the cathode of said third vacuum tube and ground; a connection between the junction of said first and second resistors and the positive terminal of a third resistor in the output circuit of said diode detector-rectifier; a connection between the cathode of said third vacuum tube and the cathode of said diode detector-rectifier; and means for maintaining the cathode of said second vacuum tube at substantially the same potential relative to ground as that of the cathode of said first'vacuum tube when no input is applied to said radio receiver.

4. In a -radio receiver, a multi-stage high-frequency vacuum-tube amplifier. the last vacuum vtube of which has its cathode in common with the cathode of a diode rectifier coupled to the output of said amplifier, and means for automatically regulating the amplification of said amplifier in accordance with changes in the directcurrent output of said diode rectifier, said means including a direct-current connection between the anode of said diode rectifier and a control electrode of at least a first and a second vacuum tube of said amplifier;a .connection between the cathode of said first vacuum tube and' the cathode of said last vacuum tube; a connection including a first and a second resistor between the cathode of said last vacuum tube and ground; a connection between the junction of said first and second resistors and the positive terminal of a third resistor in the output circuit of said diode rectifier; and means for maintaining the cathode of said second vacuum tube at substantially the same potential relative to ground as that of the cathode of said first vacuum tube when no input voltage is applied to said radio receiver.

5. In a radio receiver, means for successively delaying and increasing .the rang/,e of the amplification control `of a diode rectifier coupled to the output of a multi-stage high-frequency vacuumtube amplifier and having a direct-current connection from its anode to a control electrode of at least a first and a second vacuum tube of said amplifier, said means'including a. connection between the cathode of said first vacuum tube and the cathode of a third vacuum tube; a connection including` a first and a second resistor between the cathode of said third vacuum tube and ground; a, connection between the junction of said first and second resistors and the positive terminal of a third resistor in the output circuit of said diode rectifier; a connection between the cathode of said 4third vacuum tube and the cathode of said diode rectifier; and means for maintaining the cathode of' said second vacuum tube at substantially the same potential relative to ground as that of the cathode of said first vacuum tube when no input voltage is applied to said radio receiver.

6. In a radioreceiver, plural high-frequency amplifying tubes and a detector, means including a diode rectifier for automatic control of the amplification of at least some of said vacuum tubes, and means whereby one of said controlled tubes acts additionally as a direct-current amplifier to increase the degree of control exerted upon at least one other of said vacuum tubes by said automatic control means.

7. In a radio receiver, plural high-frequency amplifying 4tubes and a detector-rectifier, means for automatic control of the amplification of at vleast some of said vacuum tubes, and means whereby one of said controlled tubes acts additionally as a direct-current amplifier to increase the degree of control exerted upon at least one .other of said vacuum tubes by said automatic control means.

8.'In a multi-stage amplifier, plural amplifying vacuum tubes, means for automatic control of the amplification of at least some of said vacuum tubes including a. rectifier coupled to the output of said amplifier, and means whereby one of said controlled tubes, in the presence of an input signal to said amplifier exceeding a pre-determined minimum value, acts additionally as a direct-current amplifier to increase the degree of control exerted upon at least one other of said vacuum tubes by said automatic control means.

ALFRED cRossLEY. HERBERT E. MEINEMA.