US2341325A - Diode rectifier circuit - Google Patents

Description

Feb. s, 1944. KE EF KE 2,341,325

DIODE'RECTIFIER'CIRCUITS Filed Aug. 29, 1942 I CONVERTER fujF/ER Inventori Edwin W. Ken efake,

i l ttoPney.

Patented Feb. 8, 1944 DIODE RECTIFIER CIRCUIT Edwin W. Kenefake, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 29, 1942, Serial No. 456,661

4 Claims.

My invention relates to diode rectifier circuits, and particularly to circuits of this type adapted to detect signal modulations upon a high frequency carrier wave and to supply the demodulated signal indications to the audio frequency amplification stage of an electric signal receiver, such as a radio receiver, carrier current apparatus, or the like.

The invention will be found to have particular application to balanced diode detector circuits arranged to supply equal and opposite signal potentials at audio frequency to the input of a pair of balanced or push-pull audio frequency amplifying devices. It is well understood that when a balanced or push-pull audio frequency signal indication is obtained from a single diode rectifier, the voltage to ground across the diode load is no more than one-half the maximum which may be obtained if only a single-ended audio amplifier were used. Where a negative bias potential is to be obtained from the detector load for some control purpose such as automatic volume control or carrier-off noise suppression, such a reduction of maximum voltage to ground is disadvantageous.

Accordingly, it is an object of my invention to provide a new and improved single diode balanced detection circuit particularly arranged to facilitate the procurement of direct current bias potentials greater than those appearing across the diode load.

It is a further object of my invention to provide means for substantially insulating a single diode balanced detection circuit from the supply source in respect to unidirectional and signal frequency potentials, thereby to facilitate efficient automatic volume control and carrier-off noise suppression.

It is a specific object of my invention to provide a pair of single diode rectifier circuits insulated from each other with respect to unidirectional potentials and arranged independently to supply a balanced audio input circuit and a maximum automatic volume control bias potencarrier current appearing upon a conductor Ill. The signal modulated high frequency oscillations appearing upon the conductor II] are supplied to a converter or mixer II where they are combined in accordance with the heterodyning process with high frequency oscillations of a different frequency from a local oscillator I2. From the converter II a signal modulated Wave of resulting intermediate frequency is supplied to an intermediate frequency amplifier I3, and from the amplifier I3 to an intermediate frequency output transformer I4. The primary and secondary windings of the intermediate frequency transformer I4 are connected in parallel circuit relation with tuning condensers I5 and I6 respectively.

Connected to the terminals of the secondary winding of the transformer I4, is a double diode rectifier I! having a pair of anodes I8, I9 and a pair of heated cathodes 20, 2i. It will be understood of course that, if desired, a pair of single diode rectifying devices may be used in place of the double diode IT. The diode rectifier comprising the anode I9 and the cathode 2| is connected to provide a balanced or push-pull demodulated signal voltage for supply to the control grids of a double triode push-pull audio am plifier 25 having a balanced output circuit comprising an audio frequency transformer 26. The audio frequency transformer 26 is energized from the plate circuits of the double triode amplifier 25 and supplies from its secondary winding an amplified audio frequency indication to a suitable signal reproducing device such as a loudspeaker 21. a pair of separate audio amplifiers may be used to supply the balanced audio output transformer 26.

Since the diode detector circuit described briefly above utilizes only a single pair of diode elements in the double diode rectifier H, the other pair of elements comprising the cathode 20 and the anode I8 is made available for obtaining a desired bias voltage for automatic volume control and the like. For this purpose the rectifier I8, 20 may be connected in series circuit relation with a load resistor 28 across the secondary terminals of the transformer I4. The direct current bias voltage then appearing across the resistor 28 will be the maximum available from the source I4 and will be proportional in value to the strength of the incoming signal at the transformer I4. A suitable by-pass condenser 29 connected across the load resistor 28 shunts out undesired voltages of intermediate frequency and It will be understood that if desired insures that the load resistor 28 carries only direct current and audio frequency current. The secondary terminal 30 of the transformer 16 is held at ground potential for intermediate frequencies and higher frequencies so that no undesired voltage components of these frequencies appear in the automatic volume control lines 32 and 33. However, for unidirectional potentials and audio frequency potentials the point 3! is maintained at a potential below ground determined by the full drop through the load resistor 23. This negative potential is supplied by means of leads 3|, 32, and 33 to suitable stages of the signal channel ahead of the transformer M, such as the converter H and the intermediate frequency amplifier 13. The negative bias supplied through the Wires 32 and 33 controls the gain of the converter and amplifier stages in accordance with the strength of the incoming signal in such a manner as to tend to maintain substantially constant the signal volume received at the intermediate frequency transformer 14.

For the purpose of permitting the demodulating circuit through the diode rectifier l9, 2! to operate at a lesser maximum negative unidirectional potential than the point 30 in the automatic volume control circuit, the diode l9, 2! is connected directly across the secondary terminals of the transformer i4 through a pair of blocking condensers 35, 36, and the detector load is connected in shunt circuit relation to the diode i9, 2i. The condensers 35 and 33 are intermediate frequency condensers of such small ca pacity that they offer substantially no impedance to currents of intermediate or higher frequencies but effectually insulate the detector load circuit from the automatic volume control circuit and from the transformer terminal 30 for unidirectional and audio frequency potentials. The balanced detection circuit itself comprises a pair of serially connected load resistors 31, 33 having their common terminal grounded and connected as a unit in parallel circuit relation with the diode rectifier 19, 2|. Interposed between the diode rectifier l9, 2i and the diode load 31, 3-8 is an intermediate frequency by-pass filter comprising a pair of resistors 39, 40 and a capacitor ll. Since the midpoint of the resistors 31, 38 is grounded, instantaneous voltages appearing across the resistors 31, 38 are equal in magnitude and opposite in polarity. This is the condition which is necessary for supplying the input of a push-pull amplifier such as the double triode amplifier 25, and for this purpose the opposite terminals of the diode load 31, 38 are coupled through a pair of condensers 42, 43 to a pair of serially connected audio input resistors M, 45. The midtap of the resistors 43, 45 is grounded through a squelch resistor 46 and a resistor 41. The resistor 41 is connected between ground and a source of direct current supply indicated by B+. The resistor 41 thus serves as a potent1- ometer to supply through the resistor 46 a certain amount of positive bias to the midtap of the input resistors 44, 45. The midpoint of the resistors 44, 45 is also connected through the resistor 46 and a suitable grid bias resistor 33 to the common cathode 49 of the double triode aniplifier 25. Suitable taps on the audio input resistors 44, 45 are connected respectively to the control grids E! and 5| of the amplifier 25.

To provide carrier-off noise suppression, a fsquelch tube 55 is arranged to render inoperative the audio amplifier 25'upon the disappearance of a carrier wave at the transformer I l.

In the presence of a carrier wave the tube 55 is biased to cutoff by the negative potential at the terminal 30 of the transformer I4 applied to the control grid 56 of the tube 55 through a resistor 51. Upon disappearance of the carrier wave, however, the negative bias at the point 30 disappears, and the squelch tube 55 is permitted to pass current through a circuit which may be followed from a point of positive potential upon the resistor 41 through the squelch resistor 46 and the tube 55 to ground. The current flowing through this circuit is in such a direction through the resistor 46 that it drives the grids 50 and 5| of the amplifier negative with respect to the cathode 49, thereby to cut off both amplifying sections of the tube and render inoperative all subsequent portions of the transmission channel.

From the foregoing detailed description of the 20 various elements of my electric signal receiving apparatus and their manner of interconnection, it is believed that the mode of operation of the system as a whole will be readily understood. By way of summary, however, it is desired to point out certain features of the arrangement which are peculiar to applicants invention. By arranging the diode detection circuits through the rectifier l9, 2| for balanced or push-pull audio indication with the midtap of the diode load resistors 31, 38 grounded, the bias potential ode IS, 20 in a series rectifying circuit including the load resistor 28 for the procurement of a maximum negative bias potential for automatic volume control and noise suppresion. Since full negative potential at the transformer terminal 33 can be maintained only if this point is insulated from the negative terminal of the balanced detector load, the balanced load is shunt connected to the diode l9, 2| and insulated for direct current from the transformer terminal 3!! by means of the condenser 35. This arrangement permits the negative terminal of the bias resistor 28 to be operated at a different, and specifically a lower, direct current potential than the negative terminal of the balanced diode load. Thus I attain at once with only the usual two diode rectifiers the advantages of a balanced or push-pull detector and a maximum negative bias for automatic volume control and the like.

While I have illustrated only one preferred embodiment of my invention by way of illustration, many modifications will occur to those skilled in the art and it will therefore be understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention. 7

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A receiver for electric oscillations comprising a source of signal modulated carrier Waves, a first unidirectional conducting device connected to said source, a first load resistor connected in shunt circuit relation with said first. unidirectional conducting device, a second unidirectional conducting device connected to said source in seresistor having an intermediate point of fixed potential thereby to produce equal and opposite signal potentials at opposite terminal of said first resistor, a push-pull load circuit connected across said terminals, means for controlling the gain of said receiver in accordance with the potential at a point on said second load resistor, and means for isolating said second load resistor from said load circuit in respect to signal and unidirectional potentials.

2. An electric signal receiving apparatu comprising a source of signal modulated carrier waves including a tuned circuit, a first diode rectifier connected to supply a negative bias potential proportional to the strength of said signal to control said receiving apparatus, a second diode rectifier and load resistor connected in parallel circuit relation with each other and with said tuned circuit and having an output circuit connected in shunt with said load resistor to supply equal and opposite potentials with respect to ground at signal frequency, and means for substantially insulating both the anode and cathode of said second diode rectifier from said tuned circuit with respect to unidirectional and signal frequency potentials thereby isolating said bias potential from said load resistor.

3. An electric signal receiving apparatus comprising a pair of diode rectifiers, a signal chan nel for supplying to said rectifiers a signal wave modulated at audio frequency in accordance with the desired signal, one of said rectifiers being connected with a first output circuit to supply to said signal channel a negative bias potential proportional to the strength of said signal, a second output circuit connected in parallel circuit relation with the other of said rectifiers and arranged to supply equal and opposite potentials with respect to ground at audio frequency, and capacitor means connected between said second diode rectifier and said signal channel thereby substantially to insulate said second output cir cuit from said first output circuit with respect to unidirectional and audio frequency potentials.

4. An electric signal receiving apparatus comprising a signal channel including a tuned circuit for supplying a signal wav modulated at audio frequency in accordance with a desired signal, a single diode rectifier connected to said tuned circuit and having a shunt connected output circuit arranged to supply equal and opposite potentials withn'espect to ground at audio frequency, a pair of electric discharge amplifying devices having a balanced output circuit, said balanced audio frequency potentials being supplied to the input circuit of said amplifiers, a second diode rectifier connected to said tuned circuit and to a load resistor for supplying to said signal channel a negative bias potential substantially equal to the strength of said signal, and a pair of capacitors interposed between said tuned circuit and said first diode rectifier thereby electrically to insulate said balanced load circuit from said negative bias potential.

EDWIN W. KENEFAKE.

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