US2316474A

US2316474A - Amplifier control circuits

Info

Publication number: US2316474A
Application number: US333080A
Authority: US
Inventors: Jacob Van Slooten; Schenau Bernardus W Van Ingen
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-09-11
Filing date: 1940-05-03
Publication date: 1943-04-13
Anticipated expiration: 1960-04-13

Description

April 13, 1943 J. VAN sLoo'rEN y|:r AL 2,316,474 y AMPLIFIER CONTROL CIRCUITS Y Fileduay s, 1940 EXPANSION A cour/20L TUBE ,4J-1A PL. l i

25 C 0L)- v v U5 70A F 27 33 l I J l lNvEN-roR l 35 JACOB ww swarm l BERNARQUS mmnlnfusc//ENAU BYyTSg ATTORNEY Patented Apr. 13, 1943 l 2,316,474 AMPLIFIER co'N'raoL CIRCUITS Jacob van Slooten and Bernardus W. van Ingen Schenau, Eindhoven, Netherlands, assig'nors to Y Radio Corporation of Delaware Application May 3,. 1940,' Serial No. 333,080

of America, a corporation In the Netherlands Septemberll, 1939 'Z QlaimS.

This invention relates to a circuit for generating or amplifying a controlvoltage. Control voltages are used in circuits for amplifying and/or selecting a frequency-band. Thus, for example, a control voltage permits of controlling the amplification of a circuit of this character so as to -be at least substantially inversely proportioned to the input voltage supplied to the circuit. This is the so-called automatic volume control which is used with radio receivers. In this case the value of the control voltage depends on the intensity oi' the input voltage which is to be amplified. As an alternative, in a circuit serving ier the selective amplication of a fre,- quency hand a control voltage may be used for controlling the selectivity of the circuit, for example, in accordance with interfering, adjacent channel voltages.` in such a circuit control voltage may also he used for correcting tuning, the value of theV control voltage depending on the divergence between the received frequency band and the frequency to which the receiver is tuned.

Both thelatter controls are known with wireless receivers 'as Jautomatie band Width` control c the control voltage has to he derived with the aid of a diode, so that a negative control voltage y, relative to earth, to which the diode cathode is generally connected, is set up.

circuits for the use of a positive control voltage have to be' used, or positive control voltage has to be derived which after amplification results in a negative control voltage. This, however, entails the disadvantage that the'diode cathode K Vis not connected to earth.

According tothe invention the'above mentioneddifculties are obviated due to the fact thatthe circuit comprises a tube having at least one control grid, one auxiliary cathode emitting secondary electrons and one anode, to the control grld of which the control voltage to be amv pliiied, or a voltage from which the control volty age is derived, is supplied and from theauxilgenanoole detector and supplying a low frequency signal voltage to the control grid a positive cony. trol voltage for contrast expansion can be obtained at the auxiliary cathode. The advantage of thiscircuit is that a supplementary tube for En the part ci? the specication following here'- l inaiter a negative, or positive, control voltage is intended to mean avcltage which is lower or higher respectively than the voltage which is set up when the signal voltage from which the `con-- `-vfreverslrig the polarity of the control Voltage i can be: economized. t Y. In order that the invention may be clearly understood and readily carried into eiect it will now be described more vfully with reference to the accompanying drawing, in which Fig. i shows a circuit for automatic volum control Vwith amplied control voltage according to the invention, l

Fig. 2 shows a modication wherein the tube for amplifying the control voltage also serves as a. llow frequency ampliiler valve.

Fig. S shows a circuit arrangement of a low The use of such a tube offrequency amplifier Lwith contrast vexpansion according to the invention. i

Innlilg. l an intermediate frequency (I. F.) amplifier stage and adiode detector of asuperketerodyne lradio receiver are shown.` lThe intermediate frequency oscillations occurring inv an intermediate frequency' circuit l are amplied by an amplifier valve 2 and supplied to an a intermediate frequency vcircuit 3 which, jointly with an intermediate frequency circuit 4, forms a bandpass/ filter. The intermediate frequency voltage which occurs across the circuit 4v is rectiiied by a rdiode 5, and with the interposition of a resistance Sshunted by a condenser 1, supplies a direct control voltage upon which the low frequency oscillations are superposed. The low frequency voltage is supplied to a low frequency amplier (not shown) by a contact 8 slidable on the resistance 6 and a condenser 9. l.

'I'he negative control voltage occurring across the resistance 6 is supplied by a resistance I0 to the control grid II of a valve I2. The valve I2 comprises an auxiliary cathode I3 which, upon bombardment by electrons, emits secondary electrons which move to an anode I I. The auxiliary cathode I3 receives a positive voltage through a resistance I5, and is' connected to earth by a condenser I6 which has a negligible impedance. 'Ihe auxiliary cathode I3 is connected to the control grid 2Il of the amplifier valve 2 through the conductor I'l and resistance I8.

When feeble signals are being received the diode supplies only a small negative direct voltage so that an intense flow of electrons flows in the valve I2 from the cathode to the auxiliary cathode I3. Thus, the auxiliary cathode emits a lot of secondary electrons so that the potential of the auxiliary cathode is higher than the potential of the end I9 connected to the positive terminal of the source of voltage supply (not shown), of the resistance I5. The control grid of the amplier'valve 2 has the same potential as the auxiliary cathode I3, and the cathode 2| of the valve 2 has a slightly higher positive potential relative to earth due to its being connected to a point of a potentiometer 22 connected between earth and the positive terminal of a source of voltage supply.

In the case of feeble signals the valve 2 has a low negative grid voltage and a high amplification. being received the control grid II of the valve I2 is highly negative. Little current flows to the auxiliary cathode I3 and the potential of the auxiliary cathode I3 is only slightly more positive than .the potential of the point I9. Consequently, the potential of the control grid 20 is, also, less positive than'with feeble signals so that the valve 2 has but a low amplification. Referring to the drawing, the automatic volume control (AVC) is only effected on the valve 2. The auxiliary cathode I3 may, however, be connected to the control, or regulating, voltage grids of one, or more, .preceding valves (not shown) also with the interposition of resistances.

Referring to Fig. 2, in which similar parts are designated by like reference numerals, the valve I2 is also used as a low frequency, or audio, amplier valve. 'Ihe control grid II has supplied to it the control voltage to be amplied through a resistance I0, andthe low frequency alternating voltage to be amplified is f'ed through the condenser 9. Similarly to Fig. 1 the amplified control voltage is obtained from the auxiliary cathode I3. 'I'he ampliiled low frequency voltage is supplied to the low frequency I'amplifier (not shown) by a condenser 23. 'I'he anode circuit of the valve I2 comprises a resistance 24.

Fig. 3 shows the nal stage of a low frequency 6 amplier employing contrast expansion. The terminals and 28 have supplied to them audio voltage. -The terminal 23 is connected to the control gridv'of a valve 21, which comprises an auxiliary cathode 23, and to the grid of an amplifier valve 29, the anode circuit of which includes the primary of a loudspeaker transformer 30. A loudspeaker 3| is connected to the secondary of the said transformer.

If, on the contrary, powerful signals are 'is adjusted as ananode detector.

tains a screening grid 32. The terminal 26 is earthed.

The low frequency voltage which occurs between the

terminals

25 and 26 is amplified by the valve 29 and supplied to the loudspeaker 3l. The amplification of the valve 29 depends on the potential of the screening grid 32. This screening grid is connected, jointly with the auxiliary cathode 28 of the valve 21, to a point 36,01 a potentiometer 35, and has, therefore; the same potential as this auxiliary cathode. The cathode 33 of the valve 21 is connected to such a point of the potentiometer 34 that the valve 21 -The flow of electrons passing from the cathode `33 to the auxiliary cathode 28 is consequently dependent upon the value of the low frequency voltage which occurs between the

terminals

25 and 26. In the case of a high voltageV much current, and in the case of a low voltage little current, flows to the auxiliary cathode. At high voltage the potential of the auxiliary cathode 28, and thus the potential of the screening grid 32, is high so that the amplification of the valve 29 is also high; In the case of lower audio voltages on the contrary the amplification of the valve 29 decreases. 'Ihis results in contrast expansion. The advantage of the use of a valve comprising an auxiliary cathode for the generation of the control voltage required for contrast expansion resides in the fact that a diode and a separate reversing tube can be omitted.

What is claimed is:

ll. In combination with a signal voltage amplifier tube. means responsive to signal amplitude variation for controlling the gain of the amplilier, said responsive means including a tube having at least an electron emission element, a plate, a control electrode and4 a secondary electron emission electrode arranged adjacent the path of electrons flowing from said element to said plate, a direct current voltage control connection from the secondary emission electrode to said amplifier, and means for applying signal-representative voltage to said control grid.

2. In combination with a signal voltage ampliiler tube, means responsive to signal amplitude variation for controlling the gain of the amplifier, said responsive means including a tube having at least an electron emission element, a plate, a control electrode and a secondary electron emission electrode arranged adjacent the path of electrons flowing from said element to said plate, a direct current voltage control connection from the secondary emission electrode to said amplifier, and means for applying signalrepresentative voltage to said control grid. said last means including a rectifier of signals applied to said amplifier, and a direct current voltage ininection between said rectifier and control 3. In combination with a signal voltage amplier tube, means responsive to signal amplitube having at least an electron emission element,

` a plate, a control electrode and a secondary electron emission electrode arranged adjacent the path of electrons flowing from said element to said plate, a direct current voltage vcontrol connction from the secondary emission electrode to said amplifier, and means for applying signalrepresentative voltage to said control grid, said amplifier being an audio ampliiler. a source of The Valve 29 00n- A715 audio signal voltage for the amplifier. said amplitier having an auxiliary gain control electrode in addition to input and output electrodes, and said control' connection being made to said auxiliary. gain control electrode.

4. In combination with a signal voltage amplifier tube, means responsive to signal amplitude variation for controlling the gain of the amplifier, said responsiveV means including a tube havmeans impressing the detected signal voltage upon said control grid and means for deriving amplifled detected signal voltage from the plate of ing at least ari-electron emission element, a plate,-

a control electrode and a secondary electron e' emission electrode arranged adjacent the path of electrons flowing from said element to said plate, a direct current voltage control connec` tion from the secondary emission electrode tol said ampliiier, and means for applying signalrepresentative voltage to said control grid, said amplier having signal voltage input and output electrodesand said control connection being made to an/'ut electrode of said amplifier.

5. lin/combination with a signal voltage amplier'ytube, means responsive to "signal amplitude yvariation for controlling the gain of the amplilier, said responsive means including a tube having at least an electronemission element, aplate, a control electrode and a secondary electron emission electrode arranged adjacent the path of electrons flowing from said element to said plate,

said control tube.

6. In a system ofthe type having a signal source, an amplifier for the signalsl and means for utilizing amplified signals, thevxnethod of automatically controlling the gain of the amplifier which includes generating a stream of privV mary electrons or a predetermined intensity. producing a stream of secondaryelectrons with said nfirst stream, deriving a direct current voltage from said secondary electron stream, applying 'said derived voltage to said amplifier to control the gain thereof, and regulating the intensity of the gain thereof, regulating the intensity of said a direct current voltage gain control connection from the secondary emission` electrode to said amplifier, and means for applying signal-representative voltage to said control grid,a source of modulated carrier signal voltage coupled to the amplifier input electrodes, a. detector coupled to said amplier output electrodes and providing detected signal voltage, said applying said rst stream in response to amplitude variations in said signals by rectifying signals ampliiied by said amplifier and applying the rectied signal voltage to regulate said first stream intensity and deriving amplified rectified signals from said primary electron stream.

JACOB VAN SLOOTEN. BERNARDUS W. VAN INGEN SCHENAU.