US2914682A - Demodulator - Google Patents

Description

Nov. 24, 1959 J. E. TAYLOR DEMODULATOR 3 Sheets-Sheet 1 Filed Feb. l0

- Acri vm'on TRANSFER DEVICE SIGNAL -INPUT -5 DEmoDuLnToR-D` Xlvifwwllltf INVENTR Jia/1w E rA nog ATTORNEY Nov. 24, 1959 Filed Feb. 10 r1955 J. E. TAYLOR DEMODULATOR 5 Sheets-Sheet 2 lNVENTOR JOHN 5. TAYLOR Nov. 24, 1959 J. E. TAYLOR 2,914,682

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. the transistor.

r' 2,914,682 ICC Patented Nav. 24, 1959 `2,914,632 DEMoDULA'roR vJohn E. Taylor, New Milford, NJ., assignor to Bendix Aviation Corporation, Teterboro, NJ., a corporation of Delaware t Application February 10, 19755, Serial No.V 487,258 n 11 claims. `(cl. sor-sas) This invention relates to controlA circuits and more and not to be construed as defining the limits of the inparticularlyY to a demodulator which may have `an` apj plication in Servo systems. This invention is an improvement of the co-pending patent application of I ames Brook, Ser. No. 465,778, now Patent Number 2,802,976.

ItI is an object of the present invention to provide a novel demodulator employing a single current control means, such asa transistor, coupled with balanced conl Ythreeterminaloutput may be provided for a transfer device;` A further object of the invention is to provide a synchronous demodulator havingv asingle current control means such as a transistor, and Vwhereiniixed bias sup- 'plies for a Single currentcontrol means are eliminated.

' Another object is to provide a synchronousdernodulator employing at least one transistor arrangement which maybe connected with' various.biasing'networks to control'the null currentby establishing suitable operating A further object l'of the invention is to provide a novel ydemodulator, employinga transistor as the current con- ,trol means, which demodulator `is more efcient, requires lower operating voltages, is smaller in size, lighter Tin weight, generatesless heat,l has increased operating life, and is extremely.robust vr u. The invention contemplates a synchronous demodulatorremployingra transistoras'the single current control means which feeds a `pairof controlnor load windings of, atransferdevice'. Each ofthe control ,windings has rectifying means seriallvgvconnected therewith and with-a transistor having'- its ,output` element connected to la mid-point of the rectifying means, so that ,both ofthe `control windingssequentiallytime share the rvoutputof Modifications of theinvention show varif ous output configurations for'reducing vthe voltage b etwecnthe controlgwindings. The present arrangement maybe employed with a `two-or three-terminal output.

.'Ijhe foregoing and other `objects and advantages of the invention l willV `appear 1 more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein lseveralembodiments.ofthe invention are illustrated by zway'fofexample. flt is to' b.e expressly understood, however, that the drawings are for illustration purposes only variety of actuators.

' terminal output;

Fig. 3 is al modification of Fig. l showing adifferent bias arrangement; l

Fig. 4 is a modification of the invention'using a three- Fig. 5 is a modification of Fig. 4 showing a two-terminal output; f

Figs. V6 to 1 6`inclusive show representations of various waveforms. t' Y T Referring to the drawings, and more particularly to Fig. l, there is shown a block diagram havinga signal input 20 with its output coupled to a demodulator 21, and with the output of the demodulator coupled to a transfer device 22, said transfer device being coupled to an actuator 23. The transfer device may be of any suitable type, such as a differential relay or any control device wherein a two-terminal or a three-terminal output may be required. The load or control windings of the transfer device may be used to operate any offa The actuator may he a motor, a piston, a magnetic clutch, lever arrangement Aor other form of actuator. lThe actuators may include a phase sensitiveA magnetic power amplifier for driving a two-phase servo motor, a

solenoid clutch-operated servo using af constant speed The arrangement Shown in Fig. 2fhas terminals 20 `and21` whichfeed the primary of a transformer -23, which transformer has `a secondary with output-terminals24 and 25. A transistor 26 ihas a collector 27, an emitter 23, and abase 29 with said base being-connected toterminal 24 of the coupling transformer 23; while the emitter is connected to terminall 25 via aparallel circuit consisting of a resistor 30 and a capacitor 31. VA pairof diodes 32 and I33, or switchingfmeans, each have cathodes tiedV toV a common terminal v34, which in turn is connected to the collector 27. AThe plates of saiddiodes are connected, respectively, to one end of eachof said load or control windingsg35 and 36,

and with the lopposite ends ofsaid control windings being -the end thereof opposite the emitter also connected'to a mid-tap terminal 40 of `the secondary of the transformer 37. f

The surpressed carrier modulated signal s hown inFig.

`7 is fed into the circuit via terminals V2t) and 21 connected to the primary of transformer 23. Transformer 23 may be used for impedance matchingbetween the demodulator circuit and its driving means. The output of of transformer 23 is connected to the common conductor 41 and the base 29 of the transistor 26.` The action of the diodes 32 and 33, which act as selective switches, is such that during half cycle of the carrier reference, `diode 32 presents a very low impedance, while diode 33 Ipresents a very high impedence. Therefore, any current zwhich is drawn during the aforementioned half cycle will be drawn through control winding 35 of the transfer device. On the subsequent half cycle of the carrier reference,lthe aforementioned action is reversed, 'and current will be drawn only through winding 36 of the transfer device.

It will be seen that the diodes act as switches synchronized bythecarrie'r. reference toVV connect windings 35 and 36 of the transfer device in series, sequentially, with the collector 27 of transistor 26. .'Therefore, the diodes will beconducting on alternate half cycles of the carrier reference voltage. The pardlel circuit of resistor 30A and :shunt capacitor 31, which is in series with the emitter of the transistor, act to limit the actualcurrent which thetransistor will draw. Since thecathodesof both diodes are connected in common and tothe collector 27 of the transistor, 'the current in the transistor is used to control the null currents through the windings and the currents will`be balanced independently of 'the char acteristics of the transistor or current control element. The carrier reference voltage is impressed on the transformer 37, and it is a suitable predetermined frequency having a wave -form substantially `as shown in Fig. 6. At a no signal condition, the collector circuit of the transistor is a high impedance and only a small current will be drawn, At a no signal condition, the collector voltage may have the wave form substantially as shown in Fig. 8. y

At a signal condition, the base current will be substantially as shown in Fig. 9; while the collector voltage may have a wave form substantially as shown in Fig.

device `is "aphas'e sensitive synchronous demodulator which compares a modulated alternating input signal with an alternating reference voltagepf like periodicity to selectively energize one of a pair of control windings depending on the phase of the input signal which is controlled by a signal source, which source may be an ifnductive transmitting device.

In Fig. 3, parts similar to those shown in Fig. 2 have like reference numerals. Therefore, the resistor-capacitor network --31is equivalent to the resistor-capacitor network in Fig. l.A However, an additional resistor-capacitor network consisting Yof a resistor 45 and a capacitor 46 is shown with said resistor and capacitor being connected in parallel, with one end of saidV parallel circuit being connected to the terminal 25, while the opposite end of said network 45-46 is connec-ted to terminal 47, which terminal is common with conductor 41, so that the network 45-46 is in series with the terminal Z5 and the conductor 41.

` a voltage divider from the collector circuit, with capacitor 10, with an envelope portion as `showin by the dotted line 42.

j When the input signal is applied to the emitter-base junction of the transistor, the base current will be drawn for only one polarity of the input wave form. This condition is a direct result of the diode characteristics of `the emitter-basejunction. That half cycle during which the transistor base draws current, and because of the am- .plifying properties of the transistor, the impedence of the collector will be lowered. This lowered impedence will allow the collector circuit to draw an increased curi rent, -thereby increasing the current through the respective winding of the transfer device. During the half cycle .inAwhich the'base does not draw current, the impedence of the collector circuit remains high. During -that half ,cyclewhen the impedence is high, the current through the respective transfer device winding is the same as in the .absence'of signal.

, Figs. Y11 and 12 represent the current at a no signal condition through winding 35 and 36 respectively; while ,Fig Y13 shows the combined wave forms of Figs. 1l and 1 l2 representing the collector current dition. 'l V ,A Figs. 14 and 15 show current-at a'signal condition through windings 35 and 36, V`while Fig. 16 is the comat a no signal con- `bined wave forms shownin Figs. 14 and '15, which krepresent the Acollector current at a signal condition.

The action of the diodeswitch is such that for one .half cycle Vone transfer winding is operatively connected .to the collectorecircuit, and for the next half cycle, the

nothenwinding is operatively in the circuit. 'Iherefore,

Normally, the carrier reference voltage and the surpressed carrier signal are in phase with each other, but Ytheymay be 180 out of phase. If Ithe phase of the .input signal is changed by the action of the device is the same as described before except that the `additional current will be drawn through the other winding of the transfer device. Consequently, `it will be seen tittll. the

and 3.

46 acting as an alternating current by-pass, so that a bias current flows in the base 29. This bias current will cause the zero signal currents in the transfer device Windings lto increase. lThe action of the device shown in Fig. 3 is the same as that lfor the device shown in Fig. 2 for a signalninpu't, except that Ithe current in one winding instead of remaining constant at its null value will decrease from its zero signal value to a smaller value. The transfer device as shown in Fig. 3 will have twice the sensitivity of a device built in accordance with that shown in Fig. 2..V Y e The circuit arrangement shown in Fig. 4 utilizes two separate transformers 50 andv 51, each with a primary winding and a secondary winding. The secondaries of transformers 50 and 51 are each serially connected between the plate of a diode and one end of a control coil. Further, the common conductor41 is connected to the terminal 19, but in this latter showing the terminal provides a mid-tap between endsrof the two control windings Y35 and 36. Terminals 38 and 39 are connected with the series connected secondaries of the transformers 50 and 51. The remainder of the circuit shown in Fig. 4 vis similar to that shown in Fig. V2. With the showing vin Fig. 4, the voltagebetween windings 35 and 36 of the transfer device is reduced Yby establishing a common return for the control windings of the transfer device. The operation of this device is the same as that explained for Fig. 2. However, the modification of Fig. 3 over Fig. 2 may also be used in relation to Fig. 4 wherein a resistor, such as 48 (Fig. 3)*rnaybe used.

The modifications in Fig. 5 over Fig. l4 are concerned in the arrangement of providing a two-terminal output, such as terminals 55 and 56 of Fig. 5, as distinguished from the threelterminals 55, 56, and 19 for the output Yof Fig. 4. The operationY of aV device built in accordance withthecircuitry shown in Fig. 5 is slightly different from that of Fig.2. 'For the circuit of Fig. 5 at null, or zero input signal, the voltageV V1Yac`ross resistor 60 is equal and opposite to the voltage V-Z across resistor 61. Therefore, Vthere will be no Vcurrent flowing through wind- ` ings 35 and 36 of the transfer-device-at a no signal condition. At a signal condition, vthe voltage across one resistor will increase, and the voltage across the other -resistorV will remain constant or decrease according to the method of biasing used, Vsuch fas shown in Figs. 2 For a changein signal .input of 180, the polarity 'of the `output voltage will reverse, thereby causing a iiow of current through vwindings 35 and 36 'of the transfer device in the .opposite direction. The magnitude of the currents owwill beproportionate `to the magnitude of the input signal. Thedirection` of `current will be controlled by the relative phase of the input signal. Y

The device is current operated with a high output impedence, and, consequently, the device will be suited to drive a current operated transducer. p l

In both Figs. 4 and 5, as indicated inthe drawings, the instantaneous polarity of the primary and secondary windings of transformers 50 and 51 are shown by the plus and minus symbols. It will be noted that diode 32 has its plate connected to one end of the secondary winding of the transformer 50, with the polarity of that particular end of the secondary having a plus sign; While the end rof the, secondary winding of transformer 51, which is connected to the plate of the diode 33, has a minus indication with rthe instantaneous polarity indications as shownI in Figs. 4 and5.l

It will be seen thatV at any given instant, while diode 32 is conducting, diode 33 will not be conducting, and while diode 33 is-conducting, diode 32 `will not be lconducting. Depending-on the phase of the inputl signal, one of coils 35 and 36 will conduct more than the other to permit a greater current ow through the respective,

winding accordingly.V Throughout the various circuits, the device produces equal currents in both control windings at quiescent condition. At signal condition, the

` control windings will have one or the other thereof venergized dependingon thegphase of the modulated input signal. Consequently, the control windings can control operation of a transfer device which may be used in a servo system to drivel `one element to angular agreement with another element.' 1

Relating to Figs. 4 and 5, the resultant unbalanced voltage across terminals 55 and 56 will cause a ow of current, accordingly, through windings 35 and 36 of the transfer device.

. While transformers 50l and 51 are shown in Figs. 4 and 5 as being two separate transformers, it is to be understood that this circuit will operate if only one transformer is used, with said transformer having two isolated secondary windings and only one primary winding, with the secondaries being connected to provide the polarity, as shown in Figs. 4 and 5, which would result in proper operation of the device as explained herein.

While several embodiments of the invention have been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto.

Y Various changes may also be made in the design and arrangement of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. In a control circuit for a transfer device having a pair of control windings, a pair of switching means, said control windings and switching means being connected in a balanced circuit arrangement, a single impedance current control means having its output connected to the balanced circuit arrangement for controlling operation of said switching means, means for connecting an input source to said single impedance current control means, means for connecting a source of reference voltage to said switching means and` control windings and arranged to alternately render the switching means conductive during a half cycle, and a direct current biasing arrangement including feed-back means connected to the output of the current control means and to the signal source and input return impedance means connected between the signal source and a common return in the circuit to provide differential energization of the control windings in response to a signal. Y

2. In a demodulator for a transfer device having a pair of control windings and a pair of switching means operatively connected in a balanced circuit arrangement to periodically energize one or the other of said control windings depending on the phase of a reference voltage connected therewith, an input signal source, current control means having at least a pair of elements with one of said elements thereof being connected with said balanced cir'y cuit arrangement, means for connecting said input signal source to the other of said elements of said current control means, means for connecting a source of reference voltage to said balanced circuit arrangement and arranged to alternately render the switching means conductive during a half cycle, and a direct current biasing arrangement including feed-back means connected to said one element of the current control means and to the signal periodically energize one or the other of said control windings depending on the phase of a reference voltage connected therewith, an input signal source, current control means having three elements with one of said elements thereof being connected with said balanced circuit arrangement, means for connecting said input signal source to a second of said elements, means for connecting a source of reference voltage to said balanced, circuit arrangement and arranged to alternately render the switching means conductive during a half cycle, and a direct current biasing arrangement including feed-back means connected to said one element of the current control means and to the signal source and input return impedance means connected between the signal source and a common return in the circuit to provide differential energization of the control windings in response to a signal.

5. A demodulator as set forth in claim 4 wherein said current control means is a transistor having said three elements, respectively, being a collector electrode, a base electrode and an emitter electrode.

'6. In a phase sensitive demodulator for simultaneously selectively increasing energization of one of a pair of control windings and decreasing energization of the other of said pair of control windings of a transfer device depending on the phase of a modulated alternating input signal when compared with an alternating reference voltage of a like periodicity, said demodulator including a pair of switching means, a pair of control windings and windings of a reference voltage source connected in a balanced circuit arrangement and arranged to alternately render the switching means conductive during a half cycle, a current control means having a base, a collector, and an emitter, said collector being connected to a cornmon point of said balanced circuit, and a direct current biasing arrangement including feed-back means connected to the collector and to the signal source and input return impedance means connected between the signal source and a common return in the circuit to provide differential energization of the control windings in response to a signal.

7. A demodulator as set forth in claim 6, wherein said second common point of said balanced arrangement is an electrical mid-point of a source of reference voltage'.

8. In a control circuit for a transfer device having a pair of control windings and a pair of switching means connected in a balanced circuit arrangement, a current control means having its output operatively connected with said control windings and switching means for controlling operation of said switching means, means for connecting an input source to said current control means, means for connecting a source of reference voltage to said control windings and switching means and arranged to alternately render the switching means conductive during a half cycle, and a direct current biasing arrangement including feed-back means connected to the output of the current control means and the signal source and input return impedance means connected between the signal rangement, a current control means having its output operatively connected with said control windings and switching` means for controlling operation of said switching means, means for connecting an input source to said current control means, means Vfor connecting a source of reference Voltage to said control windings and switching means and arranged to alternately render the switching means Vconductiveduring a half cycle, and a direct current biasing arrangement including feed-back means connected tothe output of the current control means and to the signal source and input return impedance means connected between the signal source and a common return in the circuit to provide differential energization of the controll windings in response to a signal.

V10. In a control circuit as set forth in claim 9 and wherein the balanced circuit arrangement produces a magnetic unbalance, and an activator is connected to s aid transfer device and is operated by the resultant ux of said magnetic unbalance. Y

11. A control circuit for a transfer device comprising a pair of control windings, a pair of switching means, said control windings and switchingmeans being connected in al balanced circuit arrangement, a current control transistor having a base, a collector and an emitter and. having its collector connected to a common point of the balanced circuit arrangement for controlling the operation of said switching means-, means for connecting an input source to the base of saidtransistor, means for connecting a sourceV of reference voltage to said switching means and control windings and arranged to render each switch means conductive in different alternateY half cycles, and a direct current biasing arrangement including feedback means connected to the collector and to the signal source and input return impedance means connected between the signal source and a common return in the circuit to provide differential energization of the control windings in response to a signal.

References Cited in the le of this patent I v UNITED STATES PATENTS Howes Oct. 24, 1950 2,535,147 Markusen Dec. 26, 1950 2,597,886 McCoy- May 27, 1952 v2,601,474 Van Zelst June 24, 1952 2,691,073 Lowman Oct. 5, 19,54 2,693,572 Chase Nov. 2, 1954 2,695,381 Darling Nov. 23, 1954 2,698,392 Herman Dec; 28, 1954 2,777,092 M andelkorn Jan. 8, 1957 2,783,384 Bright et al. Feb. 26, 1957 2,787,717 K asrnir Apr. 2, 1957 2,799,784 Harris et al. July 16, 1957 FOREIGN PATENTS 644,084 Great Britain Oct. 4, 1950 Great Britain May 23, 1951

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