US2239789A - Frequency responsive control system - Google Patents

Description

April 29, 1941. w. R. KOCH FREQUENCY RESPONSIVE CONTROL SYSTEM me; Aug. 31. 19:59

Patented Apr. 29, 1941 FREQUENCY RESPONSIVE CONTROL SYSTEM Winfield R. Koch, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application August 31, 1939, Serial No. 292,769

7 Claims.

The present invention relates to frequency responsive control systems, and more particularly to frequency responsive control networks of a type utilizing changes in the phase relationof primary and secondary circuit voltages which occur in band pass or coupled tuned circuits when applied high frequency energy departs in frequency from resonance with the tuned circuits. A system of .the character to which the present invention relates is disclosed by Seeley Patent No. 2,121,103 of June 21, 19 38.

In a system of the character referred to, a signal voltage in a primary circuit is combined vectorially with two secondary signal voltages which are substantially 180 out of phase with each other, and the resulting voltages are rectified and balanced or opposed to each other to provide a direct current controlling potential which varies in magnitude and polarity with variations in frequency of an applied signal from resonance with the tuned primary and secondary circuits, the signal voltages in the primary and secondary circuits being in phase quadrature or substantially 90 out of phase with each other at resonance.

The usual phase discriminator network used in radio receiver circuits and the like, for securing automatic frequency control voltages, requires a center tapped winding in one of the tuned circuits which, in production, is difiicult to provide. Furthermore, associated diode rectifiers and output resistors therefor tend to load the tuned circuit of a discriminator network, thus reducing the gain and selectivity of the signal transmission circuit.

It is therefore a further object of the present invention to provide a frequency responsive or phase discriminator network for high frequency signals in which center tapping and loading of any of the tuned circuits thereof are eliminated.

, It is also an object of the present invention to provide a frequency responsive or phase discriminator network in which a combined amplifier and inverter stage is provided between a tuned secondary circuit and the rectifier devices for the output or controlling potential, thereby to prevent loading of said circuit, and whereby signal voltages from said circuit are obtained substantially 180 out of phase with each other Without the necessity for center tapping the circuit.

The present invention further relates to a phase discriminator or frequency responsive control network in which a primary signal voltage is combined vectorially with two secondary signal voltages at the same frequency and'has for its further object to provide the secondary voltages in connection with a tuned secondary circuit without center tapping or loading said circuit.

The invention will, however, be better understood from the following description when considered in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawing,

Figure 1 is a schematic circuit diagram of a portion of a high frequency signal amplifying channel Provided with a phase discriminator or frequency responsive network and control circuit embodying the invention; and

Figure 2 is a similar schematic circuit diagram of a portion of the circuit of Fig. 1 showing a modification thereof.

Referring to Fig. 1, the circuit, as shown, may be considered to be a portion of an intermediate frequency amplifier of a superheterodyne receiver in which an amplifier tube 5 provides one of the intermediate frequency amplifying stages and is provided with an intermediate frequency signal input coupling transformer 6 have primary and secondary windings l and 8 tuned to the same intermediate frequency. The amplifier stage 5 may be of any suitable type and, in-the present example, is shown as including a high gain pentode amplifier tube adapted for AVC control and having a high impedance anode output circuit 9 connected with the primary winding In of an intermediate frequency coupling transformer II, the secondary of which is indicated at H. Both the primary and secondary of the transformer H are tuned by suitable fixed tuning capacitors l3 to the same intermediate frequency, and the primary winding is provided with a suitable by-pass capacitor. M to ground at the low potential side thereof.

At the high potential side of the primary winding .10, an output connection I5 is provided through a coupling capacitor I6 to the cathodes H of a diode rectifier device [8, preferably of the double diode type having an anode l9 and an anode 20 associated with the cathodes I l, as indicated.

The rectifier may be provided by any suitable means providing two rectifier devices lll9 and 11-20, and in the usual frequency discriminator network the anodes l 9 and 20 are connected with terminals ofthe secondary l2, and the secondary is center tapped to ground.

In accordance with the present invention, the secondary l 2 and the tuning capacitor l3 therefor provide a highly selective circuit which is coupled ;into a grid circuit '21 of a combined phase inverter and amplifier tube 24 between the control grid 22 and the cathode 23 thereof. In connection with the output anode 25, there is provided an anode circuit coupling resistor 26, preferably of a relatively low resistance value, and, in circuit with the cathode 23, a similar output coupling resistor 21 is provided between the cathode and ground or the negative side 28 of the anode supply means. Biasing potential for the grid 22 is provided by a tap connection 29 on the resistor 21 for the grid circuit 21 through a filter resistor 30 suitably by-passed to cathode by a capacitor 3!.

With this arrangement, intermediate frequency signals received through the band pass circuits of the network, in the present case, the tuned primary and secondary circuits of the transformer II, from the amplifier stage 5, are applied to the input grid circuit 2| of the tube 24 and provide two output voltages substantially 180 out of phase with each other across the output resistors 25 and 21 in the plate and cathode circuits, respectively. Since the resistors 25 and 21 are substantially equal, the output voltages are substantially equal and may be applied to the diode rectifiers in opposition to the primary voltage in the same manner as if the secondary l2 were tapped and connected directly with the anodes l9 and 20.

For this purpose, the anodes l9 and 20 are coupled through suitable coupling capacitors and 36 with the anode terminal 31 and the cathode terminal 38, respectively, of the resistors 26 and 21. The connection between the capacitor 35 and the terminal 31 is provided through an output voltage supply lead 53, and the connection between the coupling capacitor 35 and the termlnal 38 is provided through an output voltage supply lead 40.

The diode rectifiers may be connected in series or in shunt with their respective output resistors indicated at 42 and 43. The shunt connection is provided in the present example with the output resistor 42 connected between the anode l9 and its corresponding cathode l1, while the output resistor 43 is similarly connected between the anode 20 and its corresponding cathode. The output voltage from the resistors 42 and 43, which are effectively connected in series, is taken from output terminals indicated at 45 and 45, the latter being connected through a filter resistor 4'! to ground 48, while the terminal 45 is connected through a filter resistor 49 with a control circuit 50 in conjunction with a filter capacitor 5| for establishing a predetermined time constant in the control circuit in conjunction with the series resistance of the resistor 49. It should be understood that the control circuit return is made to the ground 48.

Since the resistors 25 and 21 are maintained at relatively low resistance values, unbalance in the system because of difierent capacities to ground are substantially prevented and, since the resistors are made substantially equal and the voltages which appear across the resistors are likewise substantially equal and of opposite polarity, the diodes are thus arranged so that there is impressed upon the diodes the vector difierence between the primary signal voltage and that appearing across the resistors 26 and 21.

At the resonant frequency of the secondary 12 the phase relation will be 90 as with the usual phase discriminator network, and the two diodes provide a D. C. voltage between the terminals 45 and 46 of substantially zero volts. For off-resonance conditions of operation, either a positive or negative voltage will appear at the terminal 45 with respect to the terminal 46, depending upon which side of resonance the frequency of the incoming signal falls, as with the usual phase discriminator circuit.

The phase inverter tube 24 is particularly effective at low frequencies when the tube reactances are high and, furthermore, permits the tuned circuit l2-l3 to be made highly selective since the load of the grid circuit is substantially zero with normal bias and signal potentials. Thus, the phase inverter tub-e not only provides balanced voltages for the diode rectifiers of the network in proper phase relation, but also prevents loading of the secondary circuit and, in addition, provides an amplified signal for the diode rectifiers.

It is obvious that the phase discriminator network and diode circuit shown may be provided in connection with any suitable high frequency amplifier and that the output voltage applied to the output circuit 48-50 may be utilized for any suitable control purpose, such as automatic frequency control in a receiver, As such circuits are known and understood, the same are not illustrated.

The signal voltages which appear across the output resistors 28 and 2'! may be utilized by connectin thereto suitable circuits indicated at 53 and 54. For example, as shown in Fig. 2, to which attention is now directed, the output voltages may be applied to a full wave detector comprising a rectifier 55 and a rectifier 56 having a common output circuit 51 and separate input circuits 58 and 59, coupled respectively, to the leads 53 and 54 through suitable coupling capacitors 60 and coupling resistor 6|.

The output circuit 51 includes a common output coupling resistor 62 provided with a bypass capacitor '63 and is coupled to an audio frequency amplifier stage comprising a tube 64 through a volume control potentiometer 65 and a coupling capacitor 66. The amplifier stage representing any suitable output circuit or utilization means for audio frequency signals from the full wave detector.

Therefore, it will be seen that, in addition to providing a balanced input circuit for the diode rectifiers, the resistors 25 and 21, in connection with the inverter stage 24, may be utilized as sources of signals for rectification or detection, llirewlisse without loading the secondary circuit While the invention has been described in connection with an intermediate frequency amplifier, it is obvious that it is not limited thereto, but

, may be used in connection with any suitable high frequency signal amplifying channel for deriving a controlling potential which varies in magitude and polarity with variations in frequency from resonance, without loading the signal suppl circuit or requiring the use of a center tap therefor.

I claim as my invention:

1. A frequency responsive control system comprising, in combination, means providing two tuned coupled signal conveying circuits resonant to substantially the same frequency, means providing a pair of diode rectifiers for deriving a control potential from said network, a control circuit coupled to said diode rectifiers, and a phase inverter stage including an amplifier tube providing a coupling means between one of said tuned circuits and said diode rectifiers, said tube having a signal input grid connected with said last named circuit and having an anode and a cathode provided with substantially equal output resistors in circuit therewith to each of which one of said diode rectifiers is coupled, thereby.

to eliminate a center tap on said circuit and to prevent loading said circuit by said rectifiers, whereby the selectivity and output voltage applied to the said rectifiers are increased.

2. A frequency responsive control system comprising, in combination, means including two tuned coupled signal conveying circuits providing a band pass filter network, means for rectifying signal voltages from said tuned circuits in opposition to provide a direct current output controlling voltage which varies in magnitude and polarity with variations in frequency of an applied signal from resonance with said tuned circuits, and a combined phase inverter and amplifier stage interposed as a coupling means between said tuned circuits and said rectifier means, said stage including a cathode circuit impedance and anode circuit impedance to which said rectifier means are coupled to receive signal potentials therefrom substantially 180 out of phase with each other.

3. A frequency responsive control system comprising, in combination, two tuned coupled high frequency circuits resonant to the same frequency, means for applying a high frequency signal to one of said circuits, means providing a pair of rectifier devices having a common electrodal coupling with said last named circuit, an amplifier tube having a high impedance signal input circuit coupled to the other of said tuned signal circuits and having an anode and a cathode, means providing substantially equal coupling impedances in circuit with said anode and said cathode, means providing separate electrodal coupling between the anode and cathode ends of said impedances, and said rectifier devices, and means for deriving a. resultant output voltage from said rectifier devices including a pair of series connected output resistors and a control circuit connected with the terminal ends of said resistors.

4. A frequency responsive control system comprising, in combination, two tuned coupled high frequency circuits resonant to the same frequency, means for applying a high frequency signal to one of said circuits, means providing a pair of rectifier devices having a common electrodal coupling with said last named circuit, an amplifier tube having a high impedance signal input circuit coupled to the other of said tuned signal circuits and having an anode and a cathode, means providing substantially equal coupling impedances in circuit with said anode and said cathode, means providing separate electrodal coupling between the anode and cathode ends of said impedances and said rectifier devices, and means for deriving and detecting a received signal from at least one of said coupling impedances.

5. A frequency responsive control system comprising, in combination, two tuned coupled high frequency circuits resonant to the same frequency, means for applying a high frequency signal to one of said circuits, means providing a pair of rectifier devices having a common electrodal coupling with said last named circuit, an amplifier tube having a high impedance signal input circuit coupled to the other of said tuned signal circuits and having an anode and a cathode, means providing substantially equal coupling impedances in circuit with said anode and said cathode, means providing separate electrodal coupling between the anode and cathode ends of said impedances and said rectifier devices, and means providing a full wave detector connected to said coupling impedances for deriving rectified signals therefrom.

6. A frequency responsive control network comprising, in combination, means providing two tuned coupled signal conveying circuits resonant to substantially the same frequency, a pair of diode rectifiers having an output circuit for deriving a control potential from said network, a phase inverter stage including an amplifier tube providing coupling means between one of said tuned circuits and said diode rectifiers, said stage including an amplifier tube having an anode, a cathode and a control grid connected to said tuned circuit, a pair of output couplingresistors of substantially equal resistance value, one in circuit with said anode and the other in circuit with said cathode, means providing a coupling connection between said resistors and the anode electrodes of said diode rectifiers, and means providing a common cathode coupling connection for said diode rectifiers with the other of said tuned circuits whereby, at resonance, a controlling potential of substantially zero voltage is applied to said control circuit.

'7. A frequency responsive control system comprising, in combination, a signal input circuit, a signal output circuit, said circuits being coupled and tuned to convey signals from said input circuit to said output circuit at substantially the same resonant frequency, an amplifier tube having a control grid provided with an input circuit connected with said output circuit whereby a relatively light load is provided on said lastnamed circuit for maintaining a predetermined relatively high selectivity characteristic therein, said tube having a cathode and an anode, means providing substantially equal output coupling impedarrces in circuit with each of said last-named electrodes, a rectifier device coupled to the anode end of one of said output impedances, a second rectifier device coupled to the cathode end of the other of said impedances, whereby two signal out-put voltages substantially out of phase with each other are applied to said rectifier devices, means providing a common signal input connection between said rectifier devices and the input circuit, and means providing an output circuit for said rectifier devices for deriving therefrom a direct current voltage which is the rectified vector sum of the input circuit voltage and the resultant of the output circuit voltages across said impedances.

WINFIELD R. KOCH.

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