US2129726A - Rectifier circuits - Google Patents

Description

Sept. 13, 1938. A, w BARBER 2,129,726

RECTIFIER CIRCUITS Filed Jan. '50, 1956 I i-i. ---||-H SOURCE OF F9 M SOURCE OF INPUT OUTPUT ,C o. DEVICE b Wmuwmm- H93 d e ii A y 4 Fig.5-

INVENTOR WMBa/Lw v, Patented Sept. 13, 1938 UNITED STATES PATENT OFFlCE 13 Claims.

This present invention of mine concerns improvements in electrical circuits. It particularly relates to methods of, and means for rectification in radio receivers and the like.

* One object of myinvention is to produce a quency wave applied to the input, is the difference between the products developed across two different load circuits.

In the past most rectifiers have been connected so that when a modulated radio frequency voltage is fed to the input, an output consisting of useful demodulation products, direct current, radio frequency and radio frequency harmonics is produced. The undesired direct current is usually removed by means of capacity coupling to following circuits and the radio frequency and its harmonics are filtered out. The capacity coupling attenuates the low frequency desired demodulation products and the radio frequency filtering attenuates the high frequency desired output to a greater or lesser extent depending on the precautions taken. My present system is simple and yet produces less attenuation of low and high frequency demodulation products than most circuits by balancing out the direct current and radio frequency voltages rather than filtering them out.

My system consists of a double diode, or two similar diodes, developing similar direct current and radio frequency voltage drops across two load 40 circuits. Across one load circuit no desired demodulation products are developed while across the other load circuit the full range of desired demodulation products is developed. In the output circuit the drops across the two load circuits 5 are subtracted, cancelling out the direct current and radio frequency voltages but producing an 'unattenuated full range of desired demodulation products.

The appended claims set forth, in particular, the novel features tobe found in this invention. The following description, however, when taken in connection with the drawing, will serve to set forth the theory and mode of operation of my invention.

In the drawing,

Fig. 1 shows a circuit embodying my present invention- Fig. 2 shows another form of my invention.

Fig. 3 shows a curve representing a modulated radio frequency'wave. 5

Fig. 4 shows curves useful ,in explaining the operation of the circuit of Fig. 1.

Fig. 5 shows curves useful in explaining the operation of the circuit of Fig. 2.

In Fig. 1 I have shown a circuit embodying 'my present invention. A coil I receives a voltage from the source of input signal which may be'a radio receiver up to the second detector or it may be any other carrier wave amplifying or coupling device. Coil I is magnetically coupled to coil 2 although other types of coupling may be used, as for instance capacity coupling. One end of coil 2 is connected to the two cathodes 4 and 5 of the thermionic vacuum tube 3. Cathodes 4 and 5 may be a single common cathode since they are connected together. The other end of coil 2 is connected to the two plates or anodes (Sand 9 thru independent load circuits. The anode end of coil 2 is connected to anode 6 oftube 3 thru the impedance of resistor "l paralleled by condenser 8. Anode 6 is also connected to reference potential or ground point G. The anode end of coil 2 is also connected to the second anode 9 of tube 3 thru the impedance of resistor If] and condenser H .in parallel. An 0 output device which willusually be an audio frequency amplifier, is connected between anode 9 and ground or reference point G at [2 and I3 respectively.

When a voltage is induced in coil 2, rectification takes place due to the action of the diodes formed by cathode 4 and anode 6 and by cathode 5 and anode 9. The rectification causes condensers 8 and H to charge up to the peak value of the voltage appearing across coil 2 less the drop across the rectifying diode. If the voltage across coil 2 varies as in the case of a modulated radio frequency voltage, condenser 8 discharges thru resistor 1 when the voltage decreases and charges thru the diode consisting of cathode 4 and anode B when the voltage increases. How completely the rectified voltage across condenser 8 follows the modulation of the voltage across coil 2 is determined by the product of the ca pacity of condenser 8 multiplied by the resistance of resistor l and the frequency of the voltage change. The above condition also holds for the voltage appearing across condenser E i. Specifically, if

equals about one tenth, then about ten percent of the voltage change across coil 2 will appear across the load circuit while if is about eight or greater, the load drop will almost completely follow the voltage variations across coil 2. In the above formula t is the time of one period of the voltage variation, is the capacity of the load condenser and 1' is the re sistance of the load resistor.

Fig. 3 shows a conventional modulated wave with the modulation envelope shown. The line 0 represents the average of the radio frequency voltage, b the peak amplitude of the modulated wave and a the modulation envelope. Now, if

for condenser 8 and resistor I of Fig. 1 at the lowest modulation frequency is one tenth or less, the voltage across condenser 8 will be maintained substantially equal to ob the peak of the modulated wave since it will not follow the modulation envelope. Fig. 4 shows line d representing the voltage across condenser 8 under these conditions where 011 equals ob of Fig. 3. Now, if

for condenser H and resistor I0 is eight or more for the highest modulation frequency, the voltage across the condenser H will follow the modulation envelope of Fig. 3. The voltage across condenser l I is shown by the difference between d and e of Fig. 4. If point G at anode 6 is taken as a reference point, the coil end of condenser 8 will have a voltage 0d with reference to point G and the voltage across condenser II will subtract from the voltage across condenser 8 leaving a net voltage between anode 9 and ground G equal to ac as shown in Fig. 4. This net rectified output voltage shows the cancellation of direct current in such a way that, except for sudden changes in modulation, the negative peaks are always on the zero axis. This permits direct conductive coupling of the detector to a following tube as shown by grid H in the output device of Fig. 1. Also, since the radio frequency voltage drops across the two resistor-condenser loads are opposed. the radio frequency voltage in the output is less than that in simple diode circuits. This direct coupling and reduced radiofrequency permits reduced attenuation of both low and high modulation frequencies over conventional rectifier circuits. The coil end of resistor I may be used as a source of automatic volume control voltage although in general phase reversing means will be necessary.

The circuit shown in Fig. 2 is similar in theory and operation to that of Fig. 1 except that the rectification products are reversed in phase. Fig. 5 shows curve as the drop across the larger time constant load circuit, curve in the drop across the other load circuit and oh the net output voltage between cathode 5 and ground G. This output is similar to the output from the circuit of Fig. 1 except for the reversal in phase. This reversal in phase is accomplished in Fig. 2 by interchanging cathodes and anodes of the two diodes. Anodes 6 and 9 are connected directly to one end of the input coil 2 while cathode 4 is connected to the other end of coil 2 thru resistor T paralleled by condenser 8, and cathode 5 is connected to the cathode end of coil 2 thru resistor Ill paralleled by condenser ll. Cathode 4 is connected to the reference potential point G. Fig. 2 is adapted to direct automatic volume control by using the drop across condenser 8 since the coil end of condenser 8 is negative with respect to ground G and may be connected by lead I5 to the control grids of amplifying tubes preceeding or following the rectifier. Switch I4 is shown to open or close the discharge path of condenser 8 thru the resistor I. If this rectifier is used in a radio receiver, switch 14 may be opened for tuning purposes since it permits the build-up of automatic volume control voltage in accordance with the strength of the signal being tuned in and since no discharge path is provided, holds the sensitivity of the receiver constant during tuning. Under these conditions the receiver may be tuned by ear since the true selectivity is not obscured by the action of the automatic volume control as described in my copending application Serial No. 25,390 filed June 7, 1935, entitled Automatic sensitivity tuning. Switch l4 may also be used for the same purpose in series with resistor 1 of Fig. 1.

The circuits of both Fig. 1 and Fig. 2 may be used as control circuits in various ways. For instance if resistor 1 is heavily by-passed for modulation frequencies and resistor I0 is somewhat less heavily by-passed, the output of the rectifier will be a low frequency wave representing the slow changes in average modulation which may be useful as an automatic control voltage. A choice between the connection of Fig. 1 and Fig. 2 will yield the desired phase of control voltage. This form of rectifier may also be useful in expansion circuits on account of its property of frequency component selection.

While thermionic vacuum tubes have been shown and described as rectifying elements, other types of rectifiers may be used such as crystals or copper-oxide combinations.

While I have described only a few systems whereby my invention may be carried into efiect and have pointed out only a few possible variations, it will be apparent to one skilled in the art that many modifications are possible without departing from its spirit and scope as set forth in the appended claims.

What I claim is:

1. In a carrier wave receiver, a rectifying circuit including a common input impedance, a thermionic vacuum tube comprising at least one cathode connected to one end of said input impedance and two anodes, each of said anodes being connected to the other end of said input impedance thru independent load circuits, a connection between one of said anodes and a point of reference potential and a connection between the other of said anodes and an output device, wherein said load circuits are resistances shunted by condensers, the time constant of one of said load circuits being substantially greater than the time constant of the other of said load circuits.

2. In a carrier wave receiver, a rectifying clr..

cuit including common input impedance, 2. rectifier comprising two cathodes and two anodes,

direct connections between said cathodes and one end of said input impedance, independent load impedances between each anode and the other end of said input impedance, means whereby one of said anodes is maintained at a reference potential, an output circuit connected between the other'of said anodes and said point of reference potential, wherein each of said load circuits exhibits a substantially different time constant.

3. The method of generating modulation frequency voltages which comprises generating a direct current voltage proportional to the peaks of a modulated radio frequency wave, generating a second voltage proportional to the instantaneous value of the modulation envelope of said modulated radio frequency wave said second voltage comprising a modulation frequency component and a direct current component and subtracting one of said voltages from the other of said voltages to produce a modulation frequency voltage resultant having substantially no direct current component.

4. In a carrier wave receiver, a rectifying circuit including a common input impedance, two pairs of rectifying elements, a low impedance circuit between two similar rectifying elements and one end of said input impedance, independent load circuits connected between each remaining rectifying element and the other end of said input impedance, means whereby a direct current path in one of said load circuits may be opened, and additional means whereby one of said rectifying elements connected to one end of one of said load circuits is maintained at a reference potential. I

5. In a carrier wave receiver, a rectifying circuit including a common input impedance, a rectifier comprising twocathodes and two anodes, a low impedance circuit between said anodes and one end of said input impedance, independent load circuits between each of said cathodes and the other end of said input impedance, means whereby one of said cathodes is maintained at a fiXed reference potential and an output device connected between said two anodes, wherein said load circuits differ substantially in audio frequency impedance.

6. The circuit as set forth in claim wherein said point of reference potential is ground.

7. The circuit as set forth in claim 5 wherein each of said load circuits exhibits a substantially different time constant.

8. In a carrier wave receiver, a rectifying system including a source of unrectified voltage, two pairs of rectifying elements, a low impedance connection between two similar rectifying elements and one end of said voltage source, independent load circuits connected between each remaintaining rectifying element and the other end of said voltage source, a low impedance connection between one of said load connected rectifying elements and a point of fixed reference potential, means applying the voltage drop across the load circuit connected to said point of reference potential to gain control means in said receiver and additional means whereby a direct current path may be opened in the last said load circuit.

9. In a carrier wave receiver, two rectifiers receiving carrier wave impulses and producing output currents in two independent load circuits, an output circuit receiving the combined voltages developed across said load circuits connected in opposed polarity, in which the audio frequency impedances of said load circuits are substantially different.

10. A circuit for generating a. first demodulation voltage proportional to a carrier wave am.- plitude and a second demodulation voltage consisting of audio carrier modulation, comprising two non-linear electrical conductors receiving modulated carrier voltages and each producing an independent output current in independent load circuits, wherein the audio frequency impedance of one of said load circuits is substantially less than theother and means combining the demodulation voltage drops in opposed sense to form a useful output.

11. A circuit as described in claim wherein each of said load circuits comprises a resistor shunted by a condenser and further means comprising a switch in series with one of said resistors.

12. In an automatic volume controlled amplifier the combination of a rectifier including at least a cathode and an anode, a circuit connected between said cathode and said anode including at least a signal responsive circuit and a series connected condenser and a circuit shunting said condenser including at least a resistance and a switch connected in series. 7

13. In an electrical amplifier the combination of a grid controlled thermionic amplifier tube, a pair of rectifying elements, a load circuit comprising a resistor and a parallel connected condenser connected in series with each of said rectifying elements and an input circuit, a low impedance conductive connection joining one end of each of said load circuits, a low impedance conductive ground connection to the other end of one of said load circuits and a low impedance conductive connection between the other end of the other of said load circuits and the grid of said amplifier tube.

ALFRED W. BARBER.

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