US2237796A - Mixer circuit - Google Patents

Description

MIXER CIRCUIT Filed .April 2]., JEL-' mvemkov". Fcaramfd "mdch- 'my w Patented Apr. 8, 1941 UNITED STATES MIXER CIRCUIT Richard L. Smith, Schenectady, Y., assigner to General Electric Company, a corporation of New York Application April 21, 1939, Serial No. 269,304

8 Claims.

This invention relates to a method and apparatus for interconnecting circuits and more particularly to an arrangement for interconnecting a plurality of input and output circuits.

It is frequently desirable in connecting two electrical devices together to arrange the im` pedance of each device, as measured at the con nections to the other device, equal to the impedance of the other device. As is well known, this assures that power exchange will proceed at a maximum rate. It is an object of this invention to provide a method and means for interconnecting a plurality of power supplying and power consuming circuits in such a manner that each circuit is terminated in its characteristic impedance.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. l represents a circuit arrangement embodying my invention, Fig. 2 is a simplied schematic diagram of the circuit shown by Fig. 1, and Fig. 3 shows an alternative arrangement.

In Fig, 1 a source I0 of alternating voltage is represented simply as an impedance. It may be a radio or carrier current transmitter or an audio frequency amplier which is adapted to gencrate alternating voltage. 'Ihis source I0 is connected in series with an impedance II by a switching means I2 in its operating position. The source III and the impedance II are `connected in series across a pair of buses I3 and I4.

In the right hand position of the switch I2 the source I9 is entirely disconnected from the impedance II and the buse-s I3 and I4, and is loaded by an impedance I5. The impedance II and the buses I 3 and I4 are entirely disconnected from the source IIJ and are loaded or terminated by an impedance I8. It is desirable that the values of the impedances I5 and I5 be the same as the characteristic impedance of the source I0 and the same as the driving point impedance of the buses I3 and I4 as measured through the impedance I I. This is to insure that the various circuits are not disturbed in their normal operation by connection and disconnection of the source IU and the buses I3 and I4.

Sources I`I and I8 of alternating voltage are similar to the source 'I0 and are connectedto the buses I3 and I4 by means which are similar v ance, is adapted to consume power delivered from the buses I3 and I4 and is connected thereto by a switching means 20, a fixed attenuator 2l, a variable attenuator 22, and a series impedance 23. 'I'he device I9 may be a radio or carrier current receiver or an audio frequency responsive device. The switching means 20 in its left hand position connects both ends of device I9 in series with fixed attenuator 2l which in turn is connected in series with variable attenuator 22. One side of the variable attenuator 22, which is shown as a T type attenuator, is connected directly to one of the buses I3 and I4 and the other side of the variable attenuator 22 is connected through impedance 23 to the other bus.

When the switch 29 is in its right hand position an impedance 24 is connected at both ends to fixed attenuator 2| and device I9 is entirely disconnected. The impedance 24 should have the same impedance as device I9. The driving point impedance at the terminals of the fixed attenuator 2| on the same side as switch 20 should also be of the same value.

A device 25, represented simply as an impedance, is connected to the buses I3 and I4 by means similar to the means connecting device I9 and in which like parts have like reference characters.

The value of impedance II is made such that the impedance into which the source I (I works is equal to the impedance of the source itself. If the switch I2 be moved to the right hand, or 01T position, the impedance I5, which is of the same value as source IIJ is then connected in series with the impedance II. The impedance, into which any other source I'I or I8 or device I9 or 25 works, thus remains unchanged. The source Ill, when switch I2 is in the right hand position, is connected to impedance I5, whose value is the same as the impedance into which source I9 Works when transferring power to the other sources and the devices I9 and 25. Hence it appears at the source Ill as though no change in connections had been made.

When the switch 29 is moved to the right hand or olf position, the impedance 24 takes the place of the device I9 and hence it appears at the sources I9, I1 and I8 and at the device 25 as though no change had been made.

In Fig. 2, which is a schematic diagram corresponding to the circuit of Fig. 1, the impedance II), I'I, I8, I9, and 25 represent the devices between Which it is desired to transmit power. One end of each of these impedances are connected together. The impedances II and 23, one of Which is connected in series with each of the above-mentioned impedances are connected at one end into a common circuit which allows exchange of energy between any pair of the impedances I0, I1, I8, I9 and 25. The value of the impedances Il and 23 are such that the impedance, into which each of the devices I0, I1, I8, I9 and 25 works, is equal to the impedance of that device.

It is apparent that an impedance II or 23 may be divided into two equal parts, one being connected to either end of the corresponding device IIl, I1, I8, I9 or 25. The operation of the circuit obviously is not altered by such a change, except that the voltage is distributed somewhat more advantageously in the power transfer circuit. In certain installations this is of advantage where it is desired to balance the voltage of. each transmitter or receiver to ground to prevent cross talk.

Assuming that each of the impedances I0, I1, I6, I9, and 25 are equal and that each of the matching impedances II and 23 are equal, we may proceed to analyze this simplified network diagram to determine what value each impedance should have. Let R represent the impedance of impedances I0, I1, I8, I9 and 25. Let r be the numerical value of the impedances II and 23. Let n be the number of devices such as impedanoes I0, I'I, I8, I9 and 25, which it is desired to connect together. Then the necessary condition that each impedance R be terminated by its characteristic impedance is:

R-I-r R-r+n 1 Determining the proper value of 1' necessary to meet the imposed conditions:

by the method described here it is possible to connect together any number of circuitswhatever, assuring the termination of each in its characteristic impedance. The method is correct either if the impedances consist of pure resistance or if the impedances are adjustable in absolute magnitude but not in angle.

If it be desired to take account of more than the absolute values of impedance in arranging the network for condition of maximum power flow, it is necessary that the driving point im- R ].X:T jgc ,rR-I-JX-I-r-l-Jgc If the real quantities be equated, the same condition will be found necessary as was found when only the absolute value of impedance was considered above.

Or stated otherwise:

Equating the imaginary quantities will show the condition necessary to be met by the reactive components:

Solving for :c:

I :v: X

In other words, the reactive component of each impedance II or 23 must be equal in value and opposite in character to the reactive component in the impedance of the sources IB, I1, I8, o1 the devices I9 and 25.

In this last mentioned condition for maximum power flow, the reactances are, of course, equal` but they are also conjugate. That is, if the source I0 be inductive in a certain amount, the impedance II connected in series must then be capacitive in equal amount. The impedance II must at the same time have the proper resistive component, which is that fraction of the resistive component of source I0 as is expressed by the ratio of two less than the total number of sources and devices to the total number thereof.

It is unnecessary to consider the reactive components in the usual communication network, since, if they are not purely resistive, they are made substantially so by tuning. However, certain cases may occur where the reactive components must be accounted for to obtain the maximum transfer of power.

It is of course evident that attenuation is least when the minimum number of devices are interconnected for power transfer. However, attenuation has been found not to be objectionably great even for a comparatively large number of circuits. It is, of course, important, if any volume control device be connected between a source Il), or a device I9, and the remainder of the network, that it have a characteristic such that its input and output impedance remain unchanged as its attenuation is varied. It is also obvious, as has been mentioned above, that the source Ill, which has been represented by an impedance, may be suitably a carrier or radio transmitter having audio frequency or modulation superimposed upon its carrier wave. The device 25 may, of course, be a radio or carrier current receiver suitable for receiving signals such as emitted by the source I0. If the impedance of a source Ill, or a device I9, happens to be unequal to the other impedances of the system, matching transformers may be used, if desired, to connect the source or device in place of the sources or devices as shown.

Referring to Fig. 3 an alternative connection of the devices I0, I1, I8, I9, and 25 is indicated. As illustrated by this schematic diagram these devices may be connected all in series. This type of connection may be desrable where it is not necessary to balance each circuit to ground. In this circuit the impedances II and 23 are each connected in shunt to the corresponding device. For example, an impedance II is connected in shunt to source I0 and an impedance 23 is connected in shunt to device 25. It is apparent to any one skilled in the art how the circuit of Fig. 1 should be modied to change it from the parallel type of circuit as shown by Fig. 2 to the series type of circuit as shown by Fig. 3.

If R, 1', and Y11, represent the same quantities as before, the necessary condition that each impedance be terminated by its characteristic irnpedance is:

Solving for r, we find:

It is possible with the circuit of Fig. 3, as with that of Fig. 2, to take account of the angle of the impedances as well as the absolute values. Here, as before, to provide for maximum power now, the driving point impedance and the impedance of the device to which it is connected must be conjugates. Allowing R-HX, 1-}9`:c, and n to retain their former meanings, the network of Fig. 3 must satisfy the following condition to provide maximum power flow.

l l R-l-r-I-JX +3111 Tra (fi-HX) was (1i-1i If the real quantities be equated the same condition will be found necessary as was found when only the absolute value of impedance was con- Equating the imaginary quantities will show the condition necessary to be met by the reactive components:

l *1X* ,jx jXja;(1zl) When this equation is solved, we nd which is the same condition required in the type of circuit shown in Fig. 2.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto, since different modifications may be made both in` the circuit arrangement and instrumentalities ernployed, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

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

l. In combination with at least three electric translating devices, at least two of said devices being sources of electric energy and at least one of said devices being a load therefor, said devices being connected together for interow of electric power, means for transferring power between said devices including an impedance connected with each of said devices, said impedance having a value such that the driving point impedance o-f the circuit connected across the terminals of each device is equal to the characteristic impedance of said device.

2. In combination with at least three electric translating devices, at least two of said devices being sources of electric energy and at least one of said devices being a load therefor, said devices being connected together for interflow of electric power, means for transferring power between said devices including impedance connected with each of said devices, said impedance having a value such that the driving point impedance of the circuit connected across the terminals of each device and the characteristic 1mpedance of each device are coniugates.

3. -In combination with at least three electric translating devices, at least two of said devices being sources of electric energy and at least one of said devices being a load therefor, said devices being connected together for interflow of electric power, electric connections for connecting said devices including impedance connected in series with each of said devices, said impedance having a value such that the driving point impedance of the circuit connected across the terminals of each device is equal to the characteristic impedance of said device.

fi. In combination with at least three electric translating devices, at least two of said devices being sources of electric energy and at least one of said devices being a load therefor, said devices being connected together for interflow of electric power, electric connections for connecting said devices including impedance connected in shunt with each of said devices, said impedance having a value such that the driving point impedance of the circuit connected across the terminals of each device is equal to the characteristic impedance of said device.

5. In combination with at least three electric translating devices, at least two of said devices being sources of electric energy and at least one of said devices being a load therefor, said devices being connected together, electric connections between one end of each of said devices,

an impedance connected to the other end of each of said devices adapted to connect into a common circuit, the value of each of said impedances being such that the impedance across which each of said translating devices is connected is substantially equal to the characteristice impedance of said translating device.

6. In combination, at least three electric translating devices, at least two of said devices being sources of .electric energy and at least one of said devices being a load therefor, said devices being connected together, a rst series of impedances connected to one .end of each of said devices, a second series of impedances connected to the other end of each of said devices, common connections for the remaining ends of said rst series of impedances, and common connections for the remaining ends of said second series of impedances, said impedances connected to the ends of one of said devices having such value that the impedance at the terminals of said device is substantially equal to the characteristic impedance of said device, whereby maximum power flow between said devices is obtained.

7. In combination, at least three electric translating devices of equal characteristic impedance, means for transferring power between said devices including impedance connected in series with each of said devices, the ratio of the value of each of said impedances to the impedance of the corresponding one of said devices being as the ratio of two less than the total nurnber of devices to the total number of said devices.

8. In combination, at least three electric translating devices of equal characteristic impedance, means for transferring power between said devices including impedance connected in shunt with each of said devices, the ratio of the value of each of said impedances to the impedance of the corresponding one of said devices being as the ratio of the total number of devices to two less than the total number of said devices.

RICHARD L. SMITH.

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