Patent GB-1076838-A (GB)
Title: Switching systems
IPC: H03K7/02
Filed: 1964-07-07
Abstract: 1,076,838. Multiplex signalling; controlled non-linear inductors; amplitude modulators. RADIO CORPORATION OF AMERICA. July 7, 1964 [Aug. 14, 1963], No. 28022/64. Headings H3B, H3R and H4L. A switching system, whereby the outputs from a plurality of low output transducers, e.g. thermocouples, may be selectively and successively amplified and applied to a utilization means in a multiplexing manner, comprises a plurality of magnetic balanced modulators 14 arranged in a matrix array 12 of rows E/H and columns A/D, with each modulator exhibiting two stable saturation states (Fig. 3, not shown), means (not shown) for coupling a separate input signal (e.g. from the transducers) to each modulator, signal output means 24 coupled in common to all of the modulators, a plurality of row drivers 30, 32, 34 and 36 coupled individually to each of said rows to selectively drive each row to saturation in one stable state with a series of first excitation signals, and a plurality of column drivers 40, 42, 44 and 46 coupled individually to each of said columns to selectively drive each column to saturation in the other stable state with a series of second excitation signals interlaced with said first excitation signals, the modulator at the coordinate intersection of said row and column drivers being driven alternately between both of said stable saturation states to produce in the signal output means an output signal modulated by the input signal. Each balanced modulator, comprises, Fig. 2 (not shown), two magnetic elements (16) and (18) comprising ferrite cores, permalloy magnetic tape cores &c. together with the various windings wound thereon. A first excitation winding 26, connected to a row driver, is wound on the two elements with the same sense. A second excitation winding 28, connected to a column driver, is similarly wound on the two elements. An input winding (22), connected to a transducer (20), is wound on the two elements with opposite senses, and finally an output winding, connected in series with the output windings of the other modulators, is also wound on the two elements with opposite senses. The arrangement is such that with no input signal, alternate excitation of the two excitation windings in opposite directions as shown, yields no output from the output winding, due to the even harmonics of the excitation signal, which are generated in equal amounts in each part of the output winding, cancelling out, due to the opposing sense of the winding of the two parts. With an input signal, however, the amplitudes of the even harmonics which are generated in the two parts of the winding, are no longer equal and do not cancel out, and a resulting output signal is thus produced, having an amplitude proportional to the input signal. The excitation signal is a square wave at 150 kc./s. and is produced from an excitation square wave generator 50, operating at 600 kc./s., via bi-stable circuits 54. The interlacing of the excitation pulses applied to the row drivers and to the column drivers, is achieved by feeding the row drivers with the output of one stage of the bi-stable circuit 58, and feeding the column drivers with the output of the other stage of the bi-stable circuit. Each driver comprises a three input AND gate, one input of the three, being connected to accept the respective half of the excitation signal. The drivers are opened in such an order, that the modulator receiving both components of the excitation signal and being alternately switched from one stable state to the other, and so producing an output signal, changes in the order AE, AF, AG, AH, BE, BF, BG, BH, CE, CF . . . &c. The drivers are opened by signals from a switching arrangement 60, using the square wave output of a generator 70 at 500 c/s., and comprising four bi-stable circuits 62, 64, 66 and 68. Each bi-stable circuit is triggered by a negative going trailing edge of a pulse, and has two complementary outputs 1 and 0, the 1 outputs being used to trigger the succeeding bi-stable circuit. The outputs of circuits 62 and 64 are fed to the row drivers in the combinations shown, and the outputs of circuits 66 and 68 are fed to the column drivers in the combinations shown. The arrangement is such that column driver 40 is first opened for <SP>1</SP>/125 second, during which period row drivers 30, 32, 34 and 36 are successively opened for periods of <SP>1</SP>/ 500  second. Driver 42 is then opened for <SP>1</SP>/125 second, during which period row drivers 30, 32, 34 and 36 are successively opened for periods of <SP>1</SP>/500 second, and so on until each modulator has been fully excited and produced an output signal. A second harmonic output signal thus appears on the output lead 24 comprising a 300 kc./s. signal successively amplitude modulated by the outputs of all sixteen transducers, each transducer output modulating the 300 kc./s. signal for <SP>1</SP>/ 500  second. The 300 kc./s. signal is separated from the other present even harmonics by a tuned amplifier 78 and is detected in a phasesensitive detector 80, using the output of a bi-stable circuit 88 which divides the frequency of the output of generator 50 by two. The D.C. output of the detector, representing the successive outputs of the transducers, is fed to an output terminal 94, via a low-pass filter 90 and amplifier 92. Part of the signal at the output terminal 94 is fed back to the point 74 on the output lead 24, to provide the array with stabilizing negative feedback. Instead of each modulator being ascribed to one transducer, the output of a transducer may be fed to all the modulators in a row or column, Fig. 4 (not shown), using a different number of turns on each modulator, such that the transducer output may be reproduced at terminal 94 four times, but with different amplifications. Instead of operating the modulators in the given ordered sequence, a random sequence may be used by removing the switching arrangement and using a parallel input register for receiving the binary code number designating the selected modulator and connecting the register outputs to the driver gates. The switching system may also be used as a distributer, the incoming signal being applied to line 24 and circuits 78, 80, 90 and 92 being applied to each winding (22) which now act as output windings. Reference has been directed by the Comptroller to Specification 954,294.