US2248267A - Voltage limiter - Google Patents

Description

July 8,- 1941.

D. H. BACON voLTAGE LIMITERv 'Filed April 4. i959 2 Sheets-Sheet 1 lNvENToR 7A/VA Hon/AAM 5A cow ATTORNEY I July 8x D. H. BACON VOLTAGE LIMITER Filed April 4, 1939 2 Sheets-Sheet 2 Patented July 8, 1941 VOLTAGE LEVIITER Dana Howland Bacon, Arlington, Mass., assigner to National Company, Inc., Malden, Mass., a corporation of Massachusetts Application April 4, 1939, serial No. ,265,998

(ci. 25o-2e) 11 Claims.

The present invention relates to electric systems, and more particularly to systems for eliminating or rejecting undesired voltages. From a more specific aspect, the invention relates to static eliminators, or limiters, as they vare usually called, for radio-receiving systems.

Prior proposals for eliminating, in radio receivers, the peaks produced by external forces, such as static caused by disturbances in the atmosphere, or by motors and other electric machinery in the neighborhood, have been attended with some degree of success, but they have not been entirely effective, Many of these proposals have utilized a diode or similar device to block transmission of the signal through the receiving system when the signal voltages exceed normal Values. Prior systems of this kind, however, have been of such nature that only a portion of the undesired signal peaks are thus eliminated.

Anobject of the present invention is to provide a new land improved system of this character that shall eliminate theV whole undesired peaks.

One reason for the failure of prior proposals of this nature has been that the diode or similar device has been so connected into circuit that it could not respond rapidly enough to the undesired peak voltage.

A further object of the invention, therefore, is to provide a new and improved system of the above-described character that shall respond instantly.

Other and further objects will be explained hereinafter, and will be particularly pointed out in the appended claims.

The invention will now be explained in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic rView of one type of radio-receiving circuit embodying the invention; Figs. 2 to 4 are explanatory graphs; Fig. 5 is a fragmentary view similar to Fig. 1 of a modication; Fig. 6 is a view similarv to Fig. 1 employing two rectifiers for respectively eliminating the positive and negative peaks; and Fig. 7. is a graph corresponding to Fig. 3 for the circuit of Fig. 6.

Referring, first, to Fig. 1, radio signals, received by an antenna 2, are passed through'a radio-frequency amplier 4 and a first detector 6, where they are heterodyned through the medium of a beating oscillator 8, The heterodyned signals, after amplication by an intermediate-frequency amplifier I0, are demodulated by a second detector I 2 and amplied by an audio amplier I4, after which they are evidenced in telephones or a loud speaker I6. The radio re'- ceiver illustrated in Fig. 1 will serve asa setting for a description of the invention, but it will be understood that the invention is not limited 4to use with any particular type of radio-receiving circuit. The invention is of general application and could be used even in transmitters.

If the signals, when first arriving at the receiving antenna 2, or at some later point, are accompanied by static or other disturbances, these disturbances will be treated by this radio receiver in the same way as the signals themselves, and will be delivered in the telephones or loud speaker I3 in the form of clicks, fbuzzes, or other distortion.

This will be understood from Figs. 2 and 3; The signal may be assumed, when reachingthe antenna 2, to have the carrier envelope shown in Fig. 2, including noise-pulse positive and negative peaks I8 and 20. The second detector I2will rectify the signal, suppressing either the positive or the negative half. The negative half 'is' assumed to be suppressed, according to Fig. 3, but it is still accompanied by the noise peak I8.`

According to the present invention, the'peak I8 is eliminated from the rectified signal by' means of a diode valve 22 or similar deVice,'suitably connected into circuit at some suitable point. It is shown connected between the second detector I2 and the audio amplifier I4, but it may be connected elsewhere, as at the output of the intermediate-frequency amplifier l0, or vjust before theaudio stage of the receiver. In Fig. 6, for example, employing two diodes, the limiter is connected at the output of lthe intermediatei frequency amplifier.

The cathode 24 of the diode 22 is shown connected to the output of the second detector'I'Z, through an isolating condenser 26, and its anode 28 to the input of the audio amplifier I4, through an isolating condenser 3D. The positive terminal 32 of an adjustable direct-current voltage'source, such as a potentiometer 34, is connected, through a resistor 36, to the anode 28, and its negative terminal 38, through a resistor Ml, to the cathode 24. The connection of either the positive terminal from the positive terminal 32 of the potentiometer 34, through the resistor 36, the anode 28 and the cathode 24 of the diode 22, and the resistor 40, to the slider 42 at the negative terminal 38 of the potentiometer 34. Audio-signal voltages applied to the condenser 26, therefore, will be transmitted through the diode 22 in a direction opposite to the conventionally accepted positive direction of current in the direct-current circuit through the diode 22. The audio voltage appearing at the condenser 30 is thus a function of the variation in the direct current through the resistor 36, resulting from the audio signal through the diode 22, and this produces a voltage drop across the resistor 36. The audio voltage appearing at the condenser 30 becomes superimposed upon the voltage drop across the resistor 36 at the anode 28, and will appear as shown in Fig. 3; or rather, as will hereinafter appear, with the peak I8 eliminated, as in Fig. 4.

Where the limiter is connected just following' the second detector, as shown in Fig. 1, and where this second detector is of the type that delivers a pulsating audio voltage that is always positive in potential, it is obviously essential that the diode 22 or other device employed have a positive terminal 28 and a negative terminal 24, and that it be connected into the system with the negative terminal 24 disposed nearer to the antenna 2, and with the positive terminal 28 disposed nearer to the telephones or loud speaker I6. The signals received by the antenna 2 will then be transmitted through the diode or other device 22 inthe direction from the negative terminal 24 toward the positive terminal 28. Obviously, therefore, if the positive-terminal anode 26 should, at any time, become negative with respect to the negative-terminal cathode 24, as may take place for currents having too great a positive voltage, the excess voltage can not be transmitted through the diode 22, and will become eliminated from the system before the signal, shown in Fig. 4, reaches the telephones or loud speaker I6.

If, on the other hand, the second detector is of the type that delivers a pulsating audio voltage that is always negative in potential, these connections and and also the battery polarity should be reversed. The following discussion will be based upon the circuit diagram shown in Fig. 1 to x the ideas.

In order to eliminate the peak I8, or other voltages corresponding to the disturbances to be eliminated, therefore, it is merely necessary to adjust the degree to which the anode 28 is positive with respect to the cathode 24, so as to permit transmission of so much of the rectified signal as is indicated below the line 44, and to suppress the peak portion of the signal above the line 44. This may, for example, be effected by suitable choice of the resistors 36 and 4D and suitable adjustment of the slider 42 on the potentiometer 34. lThe anode 28 will then remain positive with respect to the cathode 24, and the diode 22 will be conducting, so long as the signal voltages remain below the line 44, but the anode 28 becomes immediately negative with respect to the cathode 24, and the diode 22 becomes non-conducting, the moment that the signal voltages rise above the line 44. The diode can not, therefore, transmit the peak I8, or any part of it, because it becomes instantaneously non-conductive as soon as any part of this peak voltage becomes impressed upon it.

By varying the position of the slider 42, the potential applied to the diode 22 can be varied between zero and a maximum corresponding to the positive voltage of the positive terminal 32 of the potentiometer, which may, for example, be in the neighborhood of 50 volts. The potential of the anode 28 depends upon a number of factors, principally upon the resistances of the resistors 36 and 40, the adjustment of the slider 42, and the average audio level of the signal transmitted through the condenser 26.

As an illustration, let it be assumed that it is desired to eliminate from the signal all voltages greater than one volt, as indicated by the line 44. The resistors 38 and 40 may be so chosen and the slider 42 so adjusted that the potential difference between the anode 28 and the cathode 24 of the diode 22 normally tends to be one volt. Audiosignal voltages less `than one volt will then produce variations at the condenser 30 within the one-volt limit below the line 44, and the peaks I8 above the line 44 will be eliminated by the diode 22 completely shutting off the flow of current at all times, as soon as the cathode 24 becomes positive with respect to the anode 28.

By adjusting the potentiometer 34, obviously, line 44 may be raised or lowered in Fig. 3, so as to adjust the portion of the peak I 8 to be eliminated and even, if desired, part of the so-called useful Wave itself. This latter condition will, of course, produce considerable distortion of the audio wave, but is very useful in certain applications as, for instance, when receiving intermittent code signals that do not require accurate reproduction in wave form.

According to certain prior-art devices, the diode 22 vor its equivalent has been so connected into circuit that Yit was normally non-conducting, so as never to pass any part of the useful signal, but was rendered conducting in response to undesired peak voltages, and this conducting state of the diode was utilized to eliminate the peak. Because diodes and similar devices of this nature are imperfect conductors when the anode 28 is only slightly positive with respect to the cathode 24, however, their response, at such times, is sluggish, and it is not until the anode 28 becomes positive with respect to the cathode 24 to the extent of, usually, two or three volts. that the diode 22 becomes sufficiently well Conducting. The lower part of the'peak voltage does get through the diode, therefore, before the diode can respond to the peak stimulus to block the remainder of the peak voltage. Peak-suppression according to these 4prior-art devices,'however, is relatively ineffective. A feature of the present invention resides, as above indicated, in so connecting the diode 22 or similar device into circuit that it is normally conducting in the direction from the cathode 24 to the anode 28, but becomes non-conducting upon the occurrence of undesired peak voltages. Except upon theoccurrence of these peak currents, the diode 22 is lat all times conducting in the'direction fromthe cathode 24 to the anode 28, so as always to transmit the useful audio signals of voltagessmaller than the voltage indicated by the line 44. This action of the diode 22 is definite and complete, since the diode 22 is essentially a perfect insulator when the cathode '24 is positive with respect to the anode 28. The response to undesired pea'k voltagesV is thus rendered immediate and the complete undesired peak voltages become eliminated.

It has been assumed above that the second detector I2 suppresses the negative half of the envelope shown in Fig. 2. If it should suppress the positive half, transmitting the negative half, the negative peak 20 would be eliminated by the same arrangement, with 'an interchange of the connections of the anode L28 and cathode 24 of the diode 22, and with the terminal 32 connected to a negative, instead of a positive, voltage.

The anode 28 would still be adjusted to a positive voltage with respect to the cathode 24.

The invention is not, however, conned to limiting action necessary for changes of potential that occur in one direction only. If the limiting device of the present invention were connected at some point in the intermediatefrequency ampliiier I0, for example, as illustrated in Fig. 6, where a symmetrical signal envelope would be impressed upon it, the limiting action could be arranged on both the positive and the negative sides. This would be effected with the aid of two limiting valves I and 54, the valve 5I for limiting the peaks 58 on one side of the envelope, and the Valve 54 having a similar action on the peaks 56 on the other side of the envelope. The anodes and cathodes of the valves 5| and 54 may be interchanged, in which case the battery polarity would be reversed to maintain the anodes positive.

There is a phenomenon, called contact potential, that requires at least a minimum voltage on the anode 28 of the diode 22 before electrons will travel from the cathode 24 to the anode 28. In such cases, for very small impressed signal voltages, it may become necessary, when the line 44 is moved very low down toward zero voltage, to adjust the slider 42 to a value positive with respect to the terminal 32. This may be accomplished in any desired way, as by connecting the resistor 36 to an intermediate point 46 of the potentiometer 34, as shown in Fig. 5. The slider 42 may then be adjusted to the right of the point 46.

As the static eliminator or limiter of the present invention is shown connected to the audio branch of the second detector I2, the parameters of this limiter should be taken into consideration in the design of the audio circuits and of the second detector I2. This is particularly important in the case of a diode second detector I2 of the type shown, wherein it is desirable to maintain equal loads at the condenser 26 for both direct-current and alternating-current voltages of the carrier envelope. From the practical standpoint, the limiter circuits will impose a fairly large alternating-current load, but zero direct-current load, with the action of the coupling condenser 26, and this effect may, in some cases, introduce second-detector distortion at high levels of carrier modulation. The means for overcoming this are well known. Since it is necessary only to equalize alternating-current and direct-current loads, the diiculty may be overcome by connecting the condenser 26 to an intermediate point 48 of a resistor 5I) connected to the cathode 52 of the second detector I2, instead of directly to this cathode. By thus Yconnecting to the intermediate point 48, compensation will be made for the impedance of the resistors 36 and 40 of the limiter.

Further modications will occur to persons skilled in the art and all such are considered to be within the scope and spirit of the invention, as dened in the appended claims.

What is claimed is:

1. In combination with an electric system from which it is desired to eliminate voltages having a value higher than a predetermined voltage, a tube having a cathode and an anode that is normally positive with respect to the cathode, means for transmitting negative half-wave currents in the system through the tube in the direction from the anode towards the cathode, means for rendering the anode negative with respect to the cathode upon the occurrence in the system of a voltage higher than the predetermined voltage, and means for rendering ther rendering means independent of the magnitude of the predetermined voltage. n

2. A static eliminator having, in combination with a receiving system provided with a signalreceiving portion and a signal-delivering portion, a tube having a cathode and an anode and connected with the receiving system so that signals received by the signal-receiving portion shall be transmitted through the tube in the direction from the cathode towards the anode for a positive half wave and from the anode towards the cathode for a negative half wave to the signaldeliveringv portion, means for maintaining the anode positive with respect to the cathode to a degree less than the voltage corresponding to the static to be eliminated from the signals,

and means for maintaining the said degree in-` dependent of the average magnitudes of the signals.

3. A static eliminator having, in combination with a receiving system, a condenser connected with the receiving system, a tube having a cathode and an anode and connected with the condenser so that signals received by the receiving system shall be transmitted through the condenser and the tube in the direction from the cathode towards the anode for a positive half wave and from the anode towards the cathode for a negative half wave, a potentiometer, means for connecting the positive terminal of the potentiometer to the anode, means for connecting the negative terminal of the potentiometer to the cathode, and means for adjusting the potentiometer to maintain the anode positive with respect to the cathode to a degree less than the voltage corresponding to the static to be eliminated from the signals.

4. A static eliminator having, in combination with a receiving system, a condenser connected with the receiving system, a tube having a cathode and an anode and connected with the condenser so that signals received by the receiving system shall be transmitted through the condenser and the tube in the direction from the cathode towards the anode for a positive half wave and from the anode towards the cathode for a negative half wave, a potentiometer, two resistors, means for connecting the positive terminal of the potentiometer through one of the resistors to the anode, means for connecting the negative terminal of the potentiometer through the other resistor to theV cathode, and means for adjusting the potentiometer to maintain the anode positive with respect to the cathode to a degree less than the voltage corresponding to the static to be eliminated from the signals.

5. In combination with an electric system from which it is desired to eliminate voltages having greater than an undesired magnitude, two means each having a negative terminal and a positive terminal, means for impressing upon the said respective two means voltages of substantially the said magnitude but of opposite polarity, means for transmitting the said voltages through one of the said two first-named means in the direction from the negative terminal toward the positive terminal for a positive half-wave and from the positive terminal toward the negative terminal for a negative half-wave and' through the other of the said 4two rst-named means in the direction from the negative terminal toward the positive terminal for a positive half-wave and from the positive terminal toward the negative terminal for a negative half-wave, and means for rendering the positive terminals negative with respect to the negative terminals upon the occurrence in the system of a voltage corresponding to the undesired voltage.

6. A static eliminator having, in combination with a receiving system having an intermediatefrequency amplier and a second detector, two means disposed between the intermediate-frequency amplier and the second detector and each having a negative terminal and a positive terminal, means for transmitting signals received by the receiving system through the intermediate-frequency amplifier, means for thereafter impressing the positive half-waves of the signals upon one of the rst-named means and the negative half-waves ofthe signals upon the other of the iirst-named means, means for transmitting the signals through one of the rstnamed means in the direction from the negative terminal toward the positive terminal for a positive half-wave and from the positive terminal toward the negative terminal for a negative halfwave and through the other of the said two rstnamed means in the direction from the negative terminal toward the positive terminal for a positive half-wave and from the positive terminal toward the negative terminal for a negative halfwave, and means for maintaining the positive terminals positive with respect to the negative terminals to a degree less than the voltage corresponding to the undesired voltage.

7. In combination with an electric system from which it is desired to eliminate voltages having greater than an undesired magnitude, two means each having a negative terminal and a positive terminal, means for impressing upon the said respective two means voltages of substantially the said magnitude but of opposite polarity, means for transmitting the said voltages through one of the said two first-named means in the direction from the negative terminalV toward the positive terminal for a positive half-wave and from the positive terminal toward the negative terminal for a negative half-wave and through the other of the said two rst-named means in the direction from the negative terminal toward the positive terminal for a positive half-waveV and from the positive terminal toward the negative terminal for a negative half-wave, and means for maintaining the positive terminals positive with respect to the negative terminals to a degree less than the Voltage corresponding to the undesired voltage.

8. Apparatus for eliminating undesired peaks from signal voltages having, in combination, means for establishing a current in one direction along a predetermined path to render the path conducting, with the potential established by the current varying from positive to negative from one end of the path to the other end of the path in the said direction, means for transmitting the signal currents along the path between the said ends in the opposite direction, means for maintaining the diierence of potential between the said ends of the path at a value less than the voltage corresponding to the peaks to be eliminated from the signals, and means for maintaining the said value independent of the magnitude of the signals.

. 9. Apparatus for eliminating undesired peaks fromV signal voltages having, in combination, a rectier, means whereby the rectifier recties the signal voltages to obtain a rectied signal voltage of predetermined polarity and suppresses the signal voltages of the opposite polarity, asecond rectifier, means for establishing a current in one direction through the second rectifier to render the second rectifierconducting in the op posite direction, means for transmitting the signal currents through the second rectifier in the said opposite direction, means for stopping the current to render the second rectifier non-conducting in the said opposite direction when the voltages of the currents to be transmitted through the second rectier attain values corresponding to the peaks to be eliminated from the signals,` and means for preventing the direct current component of the rectified signals from becoming impressed upon the second rectifier;

10. Apparatus for transmitting along a path signal voltages not greater than a predetermined magnitude and suppressing signal voltages greater than the said magnitude, the said apparatus having, in combination, means for rectifying the signal voltages to obtain a rectied signal voltage of predetermined polarity, means for impressing upon the path a unidirectional voltage of substantially the said magnitude to establish in the path a unidirectional current for rendering the path conducting in one direction to the rectified voltages not greater than the said magnitude and non-conducting in the said direction to the rectied voltages greater than the Vsaid magnitude, means for transmitting thefrectied voltages along thepath in the said direction, and means for maintaining the value of the unidirectional voltage independent of the said magnitude.

1l. Apparatus for transmitting voltages not greater than voltages of predetermined magnitude and suppressing voltages greater than the said magnitude having, in combination, two rectiersfeach having an anode and a cathode, means for impressing upon the rectiiiers voltages ofsubstantially the said Ymagnitude but of opposite polarity, means for transmitting the said voltages through one of the rectiers in the direction from the anode to the cathode and through the other rectifier in the direction from the cathode to the anode, and means for rendering the anodes positive with respect to the cathodes upon the occurrence of a voltage of the said magnitude. DANA H. BACON.

DISCLAIMER nd Bacon, Arlington, Mass. VOLTAGE LIMITEE. Patent dated led April 17, 1942, by the assignee, Nation 3, and 4 in said specicaton.

2,248,267.4-Dana Howla July 8, 1941. Disclamer Company, Inc. Hereby enters this disclaimer to claims 2, [Oficial Gazette May 19, 1942.]

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