US2030913A - Detecting and amplifying system - Google Patents

Description

Feb. 18, 1936. H. F. ELLIOTT DETECTING AND AMPLIFYING SYSTEM Filed April 27, 1932 INVENTOR HOZ'O/d E El /105?! BY HIS ATTORNEY Patented Feb. 18, 1936 UNITED STATES OFFICE DETECTING AND AMPLIFYING SYSTEM Harold F. Elliott, Palo Alto, Calif.

Application April 27, 1932, Serial No. 607,855

16 Claims. (01. 250-20) My invention relates to electronic amplifying and detecting systems and particularly to systems, commonly referred to as automatic volume control systems, wherein provisions are incorporated for holding the output power substantially constant. One example of the application of such a system is the reception of radio broadcast programs. It is desirable to maintain .the output of the loud speaker at substantially the same level regardless of the strength of the incoming signals in order that the effects of fading may be minimized and in order that both nearby and distant stations may be received satisfactorily without over-loading or blasting and .15 without the necessity of readjusting the volume control during the process of tuning from one station to another.

One of the objectives of my invention is the provision of a simple and effective system where- 30 by the output of a broadcast receiver, or of other electronic detecting and amplifying apparatus, may be held substantially constant over a wider range of input potentials than heretofore without the limitations and excessive complications 25 and cost characterizing previous systems. A

' feature of my invention is the provision of means whereby the tube which serves to rectify the signals, serves also to amplify the detected signals and to provide the potentials for automatic con- 30 trol of volume.

Another feature of the invention is the provision of means whereby advantage is taken of the amplification factor of the detector tube to increase the potentials supplied to the automatic 335 volume control circuits. This makes it possible to obtain potentials adequate to control the signals of very powerful local stations without overloading any of the tubes in the system and without providing additional tubes especially for auto- 40 matic control purposes.

These features make it possible to produce a radio broadcast receiver having all of the advantages of hitherto complicated systems, without any of the complications or limitations characterlzing these systems, at a cost no greater than simple receivers not possessing automatic control features.

Referring to the drawing:

Figs. 1 and 2 show in outline the elementary structures of electron tubes suitable for carrying out the objects of my invention.

- Fig. 3 shows a circuit diagram for a complete broadcast receiver of the superheterodyne type embodying one form of my invention.

{i5 Referring to Figure l, which illustrates a specially constructed tube suitable for carrying out the objects of the invention, numeral l designates the glass envelope for the tube. Numeral 2 designates the cathode which is of the uni-potential type mounted as usual within the en- 5 velope. Numeral 3 designates the connection from the lower end of the cathode, which connection may be brought outto a terminal on the base of the tube. Within the cathode is the usual filament or heater wire 4 from the ends of which ex- 10 tend connections 5-5 to exterior terminals, as will be understood. Numeral 6 designates the anode, and numeral I the connection for the same brought out to a terminal on the base. Numerals 8 and 9 designate two control grids u symmetrically arranged in the space between the cathode and the'anode. Dotted lines are used for one grid and full lines for the other in order that the construction may be shown clearly.

Numerals Ill and II designate the terminals for the two grids, also having exterior attachment through the base.

Figure 2 shows a second specially constructed tube also suitable for carrying out the objects of the invention. This tube is similar to that of Figure 1 except that an additional electrode in the form of a screen grid I2 is placed between the control grids 8 and 9 and the main anode 6. Terminal I3 is the external connection for screen Figure 3 shows a complete superheterodyn type of broadcast receiver embodying the tube of Figure 2 and incorporating the automatic volume control system whereby the objectives of my invention may be attained. Inasmuch as the general circuit arrangement shown in Fig. 3 is typical of standard superheterodyne types of broadcast receivers now in commercial use, the general circuits will be described very briefly and only those portions which are new and. novel will be described in detail.

The functions of the various tubes utilized in this receiver may be outlined as follows: Tube l4 serves to amplify the incoming signals at the frequency at which they are received. Tube 15,45

,is a detector wherein the amplified signals are mingled with the heterodyning frequency supplied by the oscillator tube l6. Tube [1 serves as an intermediate frequency amplifier wherein the heterodyned signals are amplified. Tube I8 is a second detector wherein the amplified intermediate frequency signals delivered by tube l1 are-demodulated and become audio-frequency signals. Tube I9 is an audio amplifier or power output tube V wherein I the audio-frequency signals from than I center.

second detector |8 are amplified and delivered to the loud speaker 20. Numeral 2| designates a power transformer which serves to supply the various A. C. potential required for the operation of the various tubes. Numeral 22 designates a rectifier which serves to supply the direct current potentials required for the operation of the tubes and circuits. A filter comprising capacitors 2324-25 and chokes 26 and 21 serves to smooth the pulsations from direct current delivered by rectifier 22..

Referring to the second detector tube l8, this preferably, though not necessarily, takes the form of one of the specially constructed tubes illustrated by Figs. 1 and 2. The two grids 8 and 9 are preferably connected to opposite terminals of the secondary 28 of the last intermediate frequency transformer which comprises coils 28 and 29. These coils are preferably, though not necessarily, tuned to resonance at the intermediate frequency by capacitors 30 and 3|. Coil 28 is preferably provided with a connection at its electrical This center connection on coil 28 is connected to the cathode 2 through load resistor 32 (sometimes called a grid-leak). By-pass capacitor-33 may be the stray capacitances of the circuits -associated with resistor 32 or may be an added capacitance of about 50 micro-microfarads.

Cathode 2 of tube I3 is preferably connected through a resistor 34 to a point 35 in the D. C. supplysystem which is about 100 volts negative with respect to ground. Alternating currents in the cathode circuit may be shunted to ground through by-pass capacitor '36. The anode circuit of tube |-8 may be provided with the usual RF filter comprising choke 31 and by-pass capacitor 38. The audio frequency output of tube l8 may be'passeddirectly to a translating device or may befurther amplified through suitable coupling to a succeeding stage, as shown in Figs. 3. The audio-frequency system here shown includes autotransformer 39, coupling capacitor 49 and potentiometer 4|. Direct current potentials for the anode circuit of tube l8 may be obtained from a suitable tap on potentiometer 42-43-44. Suitable potentials for the screen H of tube l8 may be obtained from another tapon the same potentiometer. By-pass capacitors 45 and 46 may be used to shunt alternating currents from these taps to ground. Biasing potential for the grid of tube l-9omay be obtained in any of the conventional ways, as for example, from a point of suitable negative potential in the D. C. supply system through the medium of the resistance-capacitance filter 4 '|-48. It will be evident to those skilled in the art that other forms of coupling may be used between tubes l8 and I9. For example, auto-transformer 39 may be replaced by a conventional transformer. Alternatively, resistance coupling may be used in place of choke or transformer coupling. The choice will depend upon the constants of the tubes employed and upon the conditions ofoperation desired. If a tube of the type shown in Fig. 1 is employed, then the screen I2- and its associated source of potential,

' including by-pass capacitor 45, may be omitted.

In order that the full benefit of the improved performance of my system may be realized, it is important that suitable'values be chosen for re- ;s istor 34 and for the potentials applied to the anode and cathode of tube l8. These should be so chosen that, in the absence of signals, cathode 2" floats at approximately ground potential. When signals are received grids 8 and 9, together with cathode'2, serve as a full wave rectifier and a charge appears across capacitor 33 and load resistor 32. This makes point 49, in the grid circuit, negative with respect to the cathode 2. The resultant negative charge on the grids 8 and 9 causes a reduction in the current flowing in the anode-cathode circuit of tube I8, and thus causes a reduction in the potential drop across resistor 34. This reduction in the potential drop in resistor 34 causes the cathode 2 more nearly to approach the potential of point 35 in the power supply system, which as hereinbefore noted, is preferably about I volts negative with respect to ground. It will be seen therefore that point 49, which is approximately at cathode potential in the absence of signals, becomes negative with respect to the cathode when signals are received, and, at the same time, the cathode becomes negative with respect to ground. Point 49 is therefore then negative with respect to ground by an amount equal to the sum of the potentials across capacitors Hand 36. This cumulative potential at point. 49 has suitable polarity for automatic volume control, and may beused for this purpose by connecting point 49 to the grid circuits of one or more ofthepreceding tubes I4, I and I1. shown in Fig. 3, this can readily be carried out through the medium of filter resistors 50, 5|, 52

and 53 and by- pass capacitors 54, 55,, 56 and 51.

This latter system of connections is similar. to those customarily employed in automatic volume control systems for broadcast receivers, and therefore need not be discussed in detail here.

The system of connections described inthe foregoing makes available for automatic volume control potentials which are considerably greater than can readily be obtained in systems which utilize merely the potentials resulting from rectification of the-signals. Many variations can be introduced in the system of connections shown in Fig. 3. For example, for certain conditions of operation, it is convenient to connect bus 55, which supplies the automatic volume control potentials to the grid circuits of tubes l4, l5 and I1, directly to the cathode 2 rather than to point 49. With such anarrangement, the automatic volume control potentials are reduced by the amount of the drop across capacitor 33.

It will be evident that the range of potential variation of the cathode 2- with respect to ground will depend upon the potentials applied to the cathode and anode, upon the value of resistor 34, upon the resistance of transformer 39 (or anyresistor substituted therefor) and upon theelectrical constants of tube l8. By the suitable choices of these various values of wide variation in operating conditions and control potentials may be obtained.

In a receiver of the type described, the detector tube |8 operates at a substantially constant level due to the sharpness of the. automatic control action. The output from the speaker is determined by the amount of amplification following the detector and. may be adjusted byany convenient method such as the customary potentiometer 4|. The input required at the antenna ture may conveniently be retained when employ-' ing my method of automatic control since it is a convenient means of regulating the receiver so that it may be made highly sensitive for distant reception, or relatively less sensitive, and consequently more quiet in operation, for local reception.

My invention is not limited to the arrangements shown, but is best defined in the following claims:

1. In a self-governing amplifier for alternating current potentials, means for amplifying the potentials, means comprising a single space discharge device with a single cathode and a single source of energy for rectifying the amplified potentials, re-amplifying the rectified potentials, andgoverning the amplifier directly by the rectified and re-amplified potentials combined serially.

2. A carrier wave amplifying and detecting system comprising means for amplifying the carrier, means comprising a single electron tube, a single potential source and impedances for rectifying the amplified carrier, re-amplifying' the rectified carrier and directly applying potentials from the rectified and re-amplified carrier cumulatively for automatic control of amplification.

3. Electronic amplifying and detecting apparatus comprising an electron tube having a cathode, anode and at least one grid for rectifying and subsequently amplifying signal currents, and an automatic volume control having potentials derived directly from said rectified and amplified signal currents applied cumulatively thereto for operating said control.

4. A radio receiver comprising a radio frequency amplifier, a rectifier and an impedance in which the current increases with increasing signals, an audio-frequency amplifier and an impedance in which the current decreases with increasing signals, and an automatic volume control, said volume control being operated by the rectified and amplified signals acting conjunctively through serial connections of the aforesaid impedances.

5. Electrical apparatus comprising an amplifier, a rectifier and re-amplifier comprising an electron tube having a single cathode, at least one anode and at least one grid, and means whereby potentials associated with rectification and re-amplification in said tube are directly applied cumulatively to control amplification.

6. In combination, in a carrier wave receiver, an amplifier having amplification control means, a rectifier whose output increases in proportion to the applied carrier, a re-amplifier whose direct current component decreases with increases in the carrier, an impedance traversed by the rectifier output, an impedance traversed by the reamplifier output, and a circuit including said impedances and amplification control means in the amplifier.

'7. The method of carrier wave reception which comprises amplifying the carrier, rectifying the amplified carrier to establish a direct current which increases with the carrier, re-amplifying the rectified carrier to establish a direct current component which decreases with the carrier, and controlling amplification by potentials derived directly from the rectified and reamplified currents acting cooperatively.

8. In combination, a carrier wave amplifier having gain control means, a grid leak detector, and means utilizing potentials derived directly from the grid currents and plate currents of the detector combined cumulatively to operate the gain control means.

9. The combination in accordance with claim 8 in which the grid leak detector is of the coplanar grid type.

10. A carrier wave receiver comprising a carrier wave amplifier with gain control means, a grid leak detector, an impedance in the grid circuit of the detector, an impedance and a source of potential in the cathode-anode circuit of the detector, the first said impedance being conductively connected to said second impedance and source of potential, and a circuit including the impedances and the gain control means.

11. A receiver in accordance with claim 10 in which the detector embodies a plurality of symmetrical intermeshed grids.

12. In combination, a carrier wave amplifier with gain control means, a. detector-amplifier comprising a cathode, at least one rectifying electrode and amplifying electrodes, an impedance-in a circuit comprising the cathode and a rectifying electrode, an impedance in a circuit comprising the cathode, a source of potential and an amplifying electrode, and a circuit comprising the impedances, a conductive connection therebetween and the gain control means.

13. The combination in accordance with claim 12 in which the source of potential has intermediate taps and connections whereby potentials applied to the carrier wave amplifier and detector-amplifier are relatively controlled.

14. The combination in accordance with claim 12 with the addition of means for controlling relatively the potentials applied from the source to the carrier wave amplifier and the detectoramplifier.

15. In combination, a carrier wave amplifier with gain control means, a detector, and means utilizing currents in the input and output circuits of the detector cumulatively to operate the gain control means; said means comprising a source of potential, an impedance in the output circuit, an impedance in the input circuit, and. a gain control circuit comprising the impedances connected serially and the gain control means.

16. The method of automatic gain control which comprises combining potential drops derived from the grid current and plate current of a. grid leak detector conductively to supply gain control potentials to an amplifier.

HAROLD F'. ELLIOTT.

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