US2239915A

US2239915A - Signal rectifier circuit

Info

Publication number: US2239915A
Application number: US268078A
Authority: US
Inventors: Hunt Seymour
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-04-15
Filing date: 1939-04-15
Publication date: 1941-04-29
Anticipated expiration: 1958-04-29

Description

April 29, 1941. s. HUNT SIGNAL RECTIFIER CIRCUII Filed April 15, 1939 CUT-OFF BIAS /Q I E AMPLIFIER 7US/GNAI. GRIDS OF PRIOR TUBES DETECTOR bub:

l E AMPLIFIER TO I. E NETWORK INVEN TOR. SEYMOUR HUNT 1 4M ATTORNEY.

Patented Apr. 29, 1941 SIGNAL RECTIFIER CIRCUIT Seymour Hunt, Jackson Heights, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application April 15, 1939, Serial No. 268,078

11 Claims. My present invention relates to signal rectifier circuits, and more particularly to signal detectors,

of the carrier degeneration type.

It is well known that the employing a tuned input circuit, in series with a load impedance furnishing audio and gain control voltages, has certain disadvantages, The diode will handle 100% modulated signals when the ratio of the alternating current to direct current loads is equal to unity. The direct current load of the diode rectifier circuit is the load resistor; the alternating current load is the load resistor in parallel with all of the automatic volume control grid resistors, the audio volume control potentiometer and the like. A small value is required for the magnitude of the load resistor so that the alternating current load has small shunting effect. However, a small value of load resistor increases the loading of the tuned input circuit feeding the diode. Hence, the designer is forced to choose a low value of load resistor with good modulation capability and heavy loading producing low gain and poor selectivity of the amplifier feeding the diode; or a high value of load resistor for a reduction of the input loading with reduced modulation capability. Additionally, the

diode itself loads the tuned circuits feeding it with the result that the selectivity and gain of the amplifier stage feeding the diode are reduced. Again, it is difficult automatically to control the gain of the pro-diode amplifier with the control voltage derived from the diode detector.

It may be stated that it is one of the main objects of my present invention to provide a diode detector circuit which utilizes a driver stage to feed signal energy thereto, and the driver stage being degenerative for the carrier whereby the diode detector may utilize a resistor load of relatively small magnitude so that the diode is capable of handling 100% modulated signals without regard to any loading effect on the tuned circuits feeding the diode detector.

Another important object of this invention is to provide a signal rectification network of the diode type, and the signal input circuit of the diode being provided in the cathode circuit of a stage constructed to function as a carrier degenerative signal transmission tube.

Another object of my invention is to provide a detector which is degenerative at the carrier, and whose cathode has an auxiliary anode associated therewith to provide a signal rectifier network for producing automatic volume control voltage. Still another object of the invention is to provide a receiving system in which the detector tube usual diode detector,

iii

has its signal grid biased substantially to cut-off, and wherein an auxiliary anode is associated with the detector cathode to provide an automatic volume control voltage source; the signal input circuit of the diode, which comprises a cathode and an auxiliary anode, being arranged in the detector cathode circuit and being tuned to the signal carrier.

Still other objects of the invention are to improve generally the-efiiciency of operation of the diode detector circuits and more especially to provide a diode rectifier which is supplied with signals from a carrier degenerative signal transmission tube, the latter arrangement being economically constructed and assembled in radio receivers.

In the drawing:

Fig. 1 illustrates an the invention;

Fig. 2 illustrates a modification of the invention.

Referring now to the accompanying drawing, wherein like reference characters in the different figures designate similar circuit elements, it is asarrangement embodying sumed' that the receiving system shown in Fig. 1

is of the superheterodyne type For example, the numeral I may designate the intermediate frequency resonant output circuit of the intermediate frequency amplifier; it being understood that the intermediate frequency can be chosen from a frequency range of to 450 kc. The rereceiver itself, of course, can be of the type used in the broadcast range of 550 to 1500 kc., although the invention is equally applicable to receivers of the multi-range type. Of course, the intermediate frequency amplifier (which is not shown to preserve simplicity of the disclosure) may be pre ceded by the usual converter network, and one or more radio frequency amplifiers may precede the converter.

The circuit 1 which is the tuned primary circuit of the intermediate frequency transformer T, and the tuned secondary 2 thereof, may be resonated to the operating intermediate frequency. The numeral 3 denotes an intermediate frequency amplifier which may be inserted, if desired, between circuit 2 and the transformer T1. Amplifier 3 is of usual construction, and includes the usual selfbiasing network 4. The primary circuit 5 of transformer T1 is resonated to the intermediate frequency, and this is also true of the tuned secondary circuit 6. The tube 1 is a tube of the multifunction type, and may, for example, be a tube of the SQ? or 6R7 type. In general, these tubes are of the duplex diode-triode type, and hence tube 1 has been denoted as comprising a cathode 8, a

signal grid 9 and a plate Hi. The numeral denotes the auxiliary diode anode to be used for diode detection, and it is to be understood that numeral ll actually consists of the two auxiliary anodes strapped together, and which is shown as a single anode in order to simplify the drawing.

The Cathode 8 provides independent electron streams to auxiliary anode H and to plate It]. The cathode 8 is connected to ground through an impedance which comprises the coil l2, the latter being shunted by condenser 13 for resonating the coil to the operating intermediate frequency. The signal grid 9 is connected to the tuned input circuit B and a biasing voltage source. The plate I is connected to a source of positive voltage B, theplate being bypassed to ground by a large bypass condenser ii. The auxiliary anode II is connected to ground through a path which includes load resistor 16, the latter being shunted by an intermediate frequency carrier by-pass condenser 1 ll. Auxiliary voltage developed across resistor I0 is transmitted to any desired type of audio frequency utilization network through the audio coupling condenser it It is to be understood that the utilization network may comprise one or more audio amplifiers followed by a reproducer.

The direct current voltage developed across load resistor N is employed for automatic gain control of the signal transmission tubes prior to the driver tube 1. Thus, lead I9 is connected to the signal grid of amplifier 3, as well as to the signal grids of tubes prior to amplifier 3. The usual pulsating voltage filter network is included in the lead 20; the latter is designated by the letters AVC to automatic volume control connection. The function of connection i9 is to decrease the gain of each signal amplifier as the carrier amplitude increases; in this way the carrier amplitude at the detector input circuit is maintained substantially uniform regardless of a wide range of signal carrier amplitude variation at the signal collector.

With the arrangement shown full gain and selectivity are secured from the driver tube and from

circuits

5, 6. The same amount of radio frequency voltage appearing across circuit G also appears across circuit |3-|Z. The triode 9-3-|ii is degenerative for the intermediate frequency carrier. The radio frequency voltage developed across tuned cathode circuit |.3-|2 is applied to the'diode anode I; the rectified current flows through resistor It. The tuned circuit |3-|2 may in itself be of infinite impedance, but looking back into the triode 9-8-40 it sees an impedance which is equal to the plate resistance divided by mu plus. 1. This impedance is very low; for example, it can be as low as 500 ohms. In other words the diode 8-H looks into a 500 ohm impedance. For this reasonv the load resistor l5 may be chosen to have a small resistance magnitude; hence, load l6 can be chosen for 100% modulation capability without regard to loading of tuned input circuits.

Since the diode 8--|I only operates on the positive half cycles, the driver triode need only supply half cycles to the diode. For this reason the signal grid '9 is biased substantially to cut off. Current will then flow through diode 5-8 on. the positive half cycles of'waves applied to signal grid 9.. This permits driver triode 9 -8-4 9.

denote that it is the to handle signals of larger magnitude. It' will,

therefore, be seen that actually a classB amplifier for the carrier.

driver triode 9 -8-48 is degenerated work. The triode detector is similar in action to the square law or power detector with the exception that it is degenerative at the carrier. If circuit |3-|2 is tuned exactly to the carrier, as in Fig. l, the circuit is degenerative (100%) to the carrier. It may be expected that the triode detector in such case is linear to the carrier, as

well as the audio. Very little carrier voltage will appear in the plate circuit; hence, a small by-pass condenser 22, about 100 mmf., can be connected across plate resistor 2!. The carrier voltage which appears in the detector plate circuit will depend on the ratio of resistor 2| to the impedance of tuned. circuitv |3--|2. If desired, coil i2 may be employed without use of the tuning condenser l3. across it enough. degenerative volt-age to linearize the detection characteristic for small amplitude signals; for strong signals the 100% degeneration is not required to linearize the characteristic since the power detector is linear for such high amplitude signals. Further, there would'be sufficient voltage developed across the untuned cathode. impedance to supply the diode rectifier and produce good control action.

If the tunedcircuit (|3-|2) impedance is high (high Q coil) it may augment the plate resistance to sucha high value that the output across the plate load 2| is very small, and almost zero. To prevent this the tuned circuit |3-|2 may be shunted by a resistor 30... Quite a low value of resistance for 30 may be used without reducing the voltage applied to the diode. This follows from the fact that the diode looks into an im pedance of say 500 ohms. A value of 50,000 ohms for resistor 30 would have small shunting eiiect on the 500 ohms impedance. If desired, a tuned circuit 40 can be placed in the cathode circuit of amplifier 3 to cause degeneration.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled inthe art that my inventionv is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. In a signal receptionnetwork, an electron ing resonated to said carrier frequency, means for maintaining said output electrode at a positive potential, an auxiliary anode operatively associated with said cathode and providing a diode for rectifying carrier signal current developedin said second tuned circuit, a load resistor connected between said anode and said point of fixedpotential, and means, for deriving from. the

The untuned coil may build up rectified current flowingthrough said load. resistor a direct current voltage whose magnitude is proportional to the carrier amplitude.

2. In a signal reception network, an electron discharge device including at least a cathode, a signal grid and an output electrode, a source of signals coupled to the signal grid, said source including a tuned circuit resonant to the operating signal carrier frequency, a second tuned circuit connected between the cathode and a point of fixed potential, said second tuned circuit being resonated to said carrier frequency, means for maintaining said output electrode at a positive potential, an auxiliary anode operatively associated with said cathode and providing a diode for rectifying carrier signal current developed in said second tuned circuit, a load resistor connected between said anode and said point'of fixed potential, means for deriving from across said load resistor a direct current voltage whose magnitude is proportional to the carrier amplitude, and means for biasing said signal grid substantially to space current cut-ofi.

3. In a signal reception network, an electron discharge device including at least a cathode, a

signal grid and an output electrode, a source of signals coupled to the signal grid, said source including a tuned circuit resonant to the operating signal carrier frequency, a second tuned circuit connected between the cathode and a point of fixed potential, said second tuned circuit being resonated to said carrier frequency, means for maintaining said output electrode at a positive potential, an auxiliary anode operatively associated with said cathode and providing a diode,

a load resistor connected between said anode and said point of fixed potential, means for deriving from across said load resistor a direct current volt-age whose magnitude is proportional to the carrier amplitude, at second load resistor connected to said output electrode, and means for deriving from across the second load resistor a voltage representative of the modulation on the signal carrier.

4. In a signal reception network, an electron discharge device including at least a cathode, a

signal grid and an output electrode, a source of signals coupled to the signal grid, said source including a tuned circuit resonant to the operating signal carrier frequency, a second tuned circuit connected between the cathode and a point of fixed potential, said second tuned circuit being resonated to said carrier frequency, means for maintaining said output electrode at a positive potential, an auxiliary anode operatively associated with said cathode and providing a diode, a load resistor connected between said anode and said point of fixed potential, means for deriving from across said load resistor a direct current voltage whose magnitude is proportional to the carrier amplitude, said second tuned circuit developing carrier voltage thereacross which is impressed on said signal grid in degenerative phase, means for deriving from across said load resistor audio voltage, and means for biasing said signal grid to cut-off.

5. In combination, in a signal detector network, a tube including at least a cathode, a plate and a signal grid therebetween, and at least one auxiliary anode adjacent the cathode to receive an electron stream therefrom which is independent of the electron stream flowing to said grid and plate, a signal carrier input circuit connected between the signal grid and a point of relatively fixed potential, a tuned circuit connected between the cathode and said point of fixed potential, said tuned circuit developing carrier voltage thereacross which is impressed on the signal grid in degenerative phase, a load resistor connected to said plate for developing audio voltage-thereacross, and a second load resistor connecting said auxiliary anode to said point of fixed potential, and means for deriving a direct current Voltage from across said second resistor which is proportional to the carrier amplitude.

6. In combination, in a signal detector network, a tube including at least a cathode, a plate and a signal grid therebetween, and at least one auxiliary anode adjacent the cathode to receive an electron stream therefrom which is independent of the electron stream flowing to said grid and plate, a signal carrier input circuit connected between the signal grid and a point of relatively fixed potential, a tuned circuit connected between the cathode and said point of fixed potential, said tuned circuit developing carrier voltage thereacross which is impressed on the signal grid in degenerative phase, a load resistor connected to said plate for developing audio voltage thereacross, and a second load resistor connecting said auxiliary anode to said point of fixed potential, means for deriving a direct current voltage from across said second resistor whichis proportional to the carrier amplitude, and said tuned circuit being resonated to the carrier, and means for normally biasing said signal grid to cut-off.

7. In combination, in a signal detector network, a tube including at least a cathode, a plate and a signal grid therebetween, and at least one auxiliary anode adjacent the cathode to receive an electron stream therefrom which is independent of the electron stream flowing to said grid and plate, a signal carrier input circuit connected between the signal grid and a point of relatively fixed potential, a reactive impedance connected between the cathode and said point of fixed potential, said reactive impedance developing carrier voltage thereacross which is impressed on the signal grid in degenerative phase, a load resistor connected to said plate for developing audio voltage thereacross, and a second load resistor connecting said auxiliary anode to said point of fixed potential, means for deriving a direct current voltage from across said second resistor which is proportional to the carrier amplitude.

8. In combination with a triode detector which is provided with a carrier-tuned input circuit, means in the space current path of the detector for developing carrier voltage which is impressed upon the detector signal grid in degenerative phase, a carrier rectifier circuit comprising a diode whose cathode is the cathode of said triode and whose anode is an auxiliary anode disposed adjacent the cathode, a load resistor in circuit with the space current path of the diode, carrier voltage developed across said means being impressed on said diode, and means for deriving the direct current voltage developed across said load resistor.

9. In a signal reception network of the type provided with a tube having at least a cathode, signal input electrode and signal output elec trode, a signal-tuned input circuit coupled to the signal input electrode and cathode, means applying a positive potential to said output electrode; the improvement which comprises a reactive impedance in the space current path of said tube for developing signal voltage which is impressed on said signal input electrode in degenerative voltage input element, a load impedance in said rectifier circuit for developing a uni-directional voltage thereacross which is derived from rectified signal voltage, and means for biasing said signal input electrode sufiiciently negative to permit said tube to function as a class B amplifier whereby it is adapted to handle signals of relatively large magnitude.

10. In a signal reception network of the type provided with a tube having at least a cathode, signal input electrode and signal output electrode, a signal-tuned input circuit coupled to the signal input electrode and cathode, means applying a positive potential to said output electrode; the improvement which comprises a reactive impedance in the space current path of said tube for developing signal voltage which is impressed on said signal input electrode in degenerative phase, a signal rectifier circuit including said reactive impedance as the signal voltage input element, a load impedance in said rectifier circuit for developing a uni-directional voltage thereaci'oss which is derived from rectified signal voltage, and said rectifier circuit including a diode whose elements are said cathode and an auxiliary anode adjacent said cathode within said tube.

11. In a signal reception network of the type provided with a tube having at least a'cathode, signal input electrode and signal output electrode, a signal-tuned input circuit coupled to the signal input electrode and cathode, means applying a positive potential to said output electrode; the improvement which comprises a reactive impedance in the space current path of said tube for developing signal voltage which is impressed on said signal input electrode in degenerative phase, a signal rectifier circuit including said reactive impedance as the signal voltage input element, and a load impedance in said rectifier circuit for developing a uni-directional voltage thereacross which is derived from rectified signal voltage, said reactive impedance consisting of a resonant circuit which is tuned to the frequency of said input circuit.

SEYMOUR HUNT.