US2171645A - Automatic volume control circuits - Google Patents

Description

Sept 5, 1939- H. A. BRoos AUTOMATIC VOLUME CONTROL CIRCUITS Filed June 25, 1937 m92 ffm mvENToR #ENAP/c .5 4. woos BY )#454 TTRNEY Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE Henricus lands, assgnor fabrieken, Eindhoven,

Adrianus Broos, Eindhoven, Netherto N. V. Philips Gloelampen- Netherlands, a corporation of the Netherlands Application June 25, 1

In Germany 5 Claims.

The invention relates to radio receiving systems with automatic and, in addition, with manual volume control.

In the usual systems with automatic volume control a negative control voltage which depends on the carrier wave amplitude of the received signal is supplied to one, or more, high, or intermediate frequency amplifying tubes. If this control voltage is taken so high that a substantially constant alternating voltage is supplied to the detector, there arises the drawback that for comparatively small carrier wave amplitudes the amplicaton is already considerably reduced with the result that noise due to Brownian movement, and the like, in the amplifying tubes is predominating. Besides, with weak signals a greater amplification is desired in order to supply to the detector a sufficiently high alternating voltage to obtain linear rectification. For these reasons it is desirable to choose the control voltage not too high, owing to which with an increasing carrier wave amplitude the alternating voltage supplied to. the detector increases slightly. A proper adjustment of the manually operated volume control device permits, nevertheless, to obtain in this case always the desired output.

With the reception of weak signals the manually operated volume control device is adjusted, in' general to a high output. When with the same adjustment a strong signal is received, considerable distortion is produced. This distortion is partly due to the fact that the low frequency amplifier is overloaded so that by adjusting the manually operated volume control device to a small output a reduction of the distortion may be obtained. As, however, the distortion also ensues from the fact that the diode detector is overloaded, it is not possible completely to remove the distortion in this way.

According to the invention, this drawback is obviated by providing a device for adjusting the control voltage for the automatic volume control which is supplied to one or more amplifying tubes, said device being mechanically coupled with the manually operated volume control device.

It is thus ensured that with any adjustment of the manually operated volume control device there is supplied to one or more amplifying tubes a control voltage such that the detector is prevented from being overloaded.

As the noise brought about due to Brownian movement, and the like, is substantially determined by the first amplifying tube of the system, it is particularly desirable to supply to the first Aamplifying tube of the system a control volt- 937, Serial No. 150,277 July 28, 1936 (Cl. Z50-20) age which depends on the adjustment of the manually operated volume control device. To the amplifying tubes which follow said tube may be supplied, if desirable, a control voltage which does not depend on this adjustment.

In a superheterodyne receiving system there may be supplied, for example, to the radio frequency amplifying tube, or tubes, a control voltage which depends on the adjustment of the manual control device, and to the intermediate frequency amplifier a control voltage which does not depend on this adjustment.

In the drawing:

Fig. 1 shows a circuit employing the invention, and

Fig. 2 is a circuit embodying a modification.

Fig. 1 represents part of a superheterodyne receiving system. The oscillations amplified by an intermediate frequency amplifying tube I are supplied to a band pass lter which consists of circuits 2 and 3 which are tuned to the intermediate frequency. The voltage across the circuit 2 is supplied through a coupling condenser I to a diode anode 5 which is arranged within a tube 6. This tube comprises, furthermore, a second diode anode l, a control grid 8, an anode 9 and a cathode I0. The oscillations supplied to the diode 5, I0 are rectified, and bring about across a resistance II a direct current voltage drop which depends on the carrier wave amplitude of the signal received. The voltage set up across the circuit 3 is supplied to the diode 1, lil which serves for the demodulation of the oscillations received. Part of the audio frequency alternating voltage set up across the resistance I2 is supplied by a coupling condenser I3 to the control grid 8 which is connected through a leakage resistance I4 and a source of negative bias 21 to the cathode. A condenser I5 forms a by-pass for the intermediate frequency oscillations. The output of the audio frequency amplifier is adjusted with the aid of a slide contact I6.

According to the invention, the direct current voltage drop across a variable part of the resistance I I is supplied as a control Voltage to the high frequency amplifier. There is provided for this purpose a slide contact Il which, as indicated by a dotted line I8, is mechanically coupled with the volume control slide contact I6. This mechanical coupling is such that a decrease of that portion of the resistance I2 which is located between the slide contact I6 and the cathode I0 results in an increase of that portion of the resistance II which is located between the slide contact I1 and the cathode I0. The slide con- "rand said controlling tact I 'I is connected through a lter, consisting of a resistance I9 and a condenser 20, to a con.- ductor 2I Which supplies the control voltage to the high frequency amplifier. When the manually operated volume control is adjusted to a, smaller output a larger proportion of the variable direct current voltage set up across the resistance II is supplied to the high frequency amplier. A control voltage which does not depend on the adjustment of the manually operated volume control is supplied to the intermediate frequency ampliiier through a lter consisting of a resistance 22 and a condenser 23 and .through a conduotor 24.

Fig. 2 represents a system which differs from the system of Fig. 1 in that the control voltage which depends on the adjustment of the manually operated volume control is obtained by making the coupling condenser 4 variable, and, as is indicated by a dotted line 2B, by mechanically coupling the condenser 4 with the manually operated volume control slide contact I6. In order to avoid that a Variation of the capacity of the coupling condenser should influence the tuning, a resistance 25-is connected in series with the coupling condenser. With a decrease of that portion of the resistance I2 which is located between the slide contact I6 and the cathodeY I 0, the capacity of the coupling condenser 4 increases; which results inthat a higheralternating voltage is supplied to the diode 5, IIJ and that, consequently, across the resistance `I I a higher direct current voltage is obtained,` A control Voltage for the intermediate frequency amplier which is independent of the adjustment of the manually operated volume control device is ob-v tained in this case by supplying the direct current voltage drop across the resistance I2 to the intermediate -frequency ampliiier.` What is claimed is: -1. In a receiver of the type employing a plurality of cascaded signal tier coupled to the last amplier, means adjustably connected to the rectiiier and functioningas a manual volume control device,ra second rectier arranged to have signals impressed thereon and adapted to derive a direct current voltage from rectified signals, means for controlling the magnitude of said voltage,v additional means conjointly actuating said manual control device that the said voltage magnitude is afunctionof the adjustment ofthe manual control device, means for applying said controlled volta-gato the rst of said cascaded amplifiers, and a connectionVv for applying the direct current V`voltage com-- ponent of the rectified output of the firs-t rectifier-Y to an amplifier following saidY iirst of said cascaded amplifiers. i Y

rality off cascaded signalamplifiers, a signal rec; tier coupled to the-last amplifier, means adjust-` ably connected to the rectier and functioning as and adapted to derive a direct current voltage ampliiiers, a signal rec means inV such VaY manner.

2. In a receiver of the type enfiploying a plu-.

magnitude of said voltage, additional means for conjointly actuating said manual control device and said controlling means in such a manner that the said voltage magnitude is a function of the adjustment of the manual control device, means for ap-plying said controlled voltage to the first of said cascaded ampliiiers, and a connection for applying the direct current voltage component of the rectied output of the first rectifier to an amplifier following said iirst of said cascaded amplifiers, said controlling means consisting of an adjustable condenser connected between the second rectifier and the Vsaid last amplier.

3. In a receiver of the type employing a plurality of cascaded signal ampliiiers, a signal rectifier coupled to the last amplifier, means adjustably connected to the rectiiier and functioning as a manual volume control device, a second rectiiier arranged to have signals impressed thereon and adapted to derive a direct current voltage from rectified signals, means for controlling the magnitude of said voltage, additional means for conjointly actuating said manual control device and said controlling means in such a manner that the said voltage magnitude is a function of the adjustment of the manual control device, means for applying said controlled Voltage vto the iirst voi said Vcascaded amplifiers, a connection for applying the direct current voltage component of the rectiiied output of the irst rectier to an am plier following said iirst of said cascaded amplifiers, an audio amplier, said manual volume control device ccnnecting the rst rectifier to said audio amplier, and a common tube envelope housing the electrodes of the two rectiers and the audio amplifier. Y Y

4. In a superheterodyne receiver of the type including cascaded radio and intermediate ampliliers, a demodulator coupled to the intermediate ampliiier andV producing automatic volume control bias for the latter and audio voltage, an audio amplifier, means controlling the magnitude of audio voltage impressed on the audio amplifier; the improvement comprising a rectifier'coupled to said intermediate amplifier and producing a second automatic Volume control bias, means applying the second bias solely to the radio amplifier, and means, responsive to said-controlling means, for adjusting the value of the second bias. 5.51.11 a superheterodyne receiver of the type including cascaded radio and intermediate ampliers, a demodulator coupled to the'intermediate amplifier and producing automatic volume control bias for the latter and audio voltage, an audio amplifier, means controlling the magnitude of audio voltage impressed on the audio amplifier; the improvement comprising a rectifier coupled to said intermediate ampliflerfand producing a second automaticvolume control bias, means applying the second bias solely to the radio amplifier, and means, responsive to said-controlling means, for adjusting the value of the second bias, said last adjusting means consisting HENRICUS ADRIANcs Baoos.

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