Patent GB-971120-A (GB)
Title: Improvements in or relating to analog encoders
IPC: H03M1/00
Filed: 1961-12-21
Abstract: 971,120. Analogue to digital converters. WESTERN ELECTRIC CO. Inc. Dec. 21, 1961 [Dec.29, 1960], No. 45786/61. Heading G4H. [Also in Divisions H3 and H4] Relates to an encoder employing differently biased bi-stable magnetic core elements in a pulse code modulation system. As shown in Fig. 1 in an encoder using a simple three-digit binary code, the first digit group comprises magnetic element 1 4  which encodes the most significant digit, the second digit group comprises magnetic elements 2 2  and 2 6  which encode the middle digit, and the third digit group comprises magnetic elements 3 1 , 3 3 , 3 5  and 3 7  which encode the least significant digit, the subscripts 1, 2, 3 &c. representing the increasing bias levels of the respective magnetic elements as determined by the code. Each magnetic element is provided with a bias winding 11 1 &c. energized from source 16, &c. drive winding 12 1  &c. controlled by drive amplifiers 17 1  &c. read winding 13 1  &c., controlled by read amplifier 13 1  &c. and output winding 14 1  &c. connected to distributer 22 supplying the transmission circuit via amplifier 23. Fig. 2 shows the bias pattern for the three digit groups, in which the total reversed flux is plotted as a function of the drive field H D1 , H D2 , H D3 , the bias level required to switch respective elements from one stable state to another being indicated by B 1 , B 3 , B 5 , B 7  for the third group, B2, B6 for the second group, and B4 for the first group. In operation the signal to be encoded is supplied to a sampling circuit 19 controlled by a clock pulse generator 21 and periodic samples of the signal are supplied to the drive amplifiers 17 1  173, 173, thus switching over all those elements in which the drive pulse exceeds the biasing level B1, B2,&c. After the drive pulse has reached its full magnitude, the read amplifiers 18, 18 2 , 18 3  produce respective read pulses which oppose the drive pulses and are of a magnitude equal to half the difference between successive bias levels in the corresponding digit group. Thus only those elements biased at levels most nearly corresponding to the magnitude of the drive field will be reset to produce output pulses in the corresponding windings 14 1 , 14 2 , 14 3  which are supplied via a distributer 22, controlled by the clock 21, and amplifier 23 to the transmission circuit. In an alternative three-digit encoder, Figs. 5 and 6, the first digit group comprises magnetic element 1 4  encoding the most significant digit, elements 2 2 , 2 4  and 2 6  encoding the middle digit, and elements 3 i  to 3 7  encoding the least significant digit, the subscript as before indicating the increasing bias levels. The groups of magnetic elements are provided with bias windings 113, 11 2 , 11 3  supplied by bias sources 16 1 , 16 2 , 16 3  respectively, and drive windings 12 1 , 12 2 , 12 3  energized by drive amplifiers 17 3  supplied with signal samples from circuit 19 controlled by clock 21. The read function is performed by the output windings 14 1 ,14 2 ,14 3  and the integrators 24 3 . The output windings in each group are arranged so that pulses produced at successive bias levels, during the drive pulses are in opposition thus producing an output from the corresponding integrator only when an odd number of elements in the respective group are switched. In Fig. 6 the reversed flux linking the output windings in the three groups is plotted against the drive field H 23 , H D2 , H D3  respectively for a simple binary code, and the bias levels required to switch the respective elements are shown as B 1  to B 7  for the third group, B 2 , B 4 , B 6  for the middle group, and B4 for the first group. Fig. 7 shows an arrangement of a single digit group in which the magnetic elements 40 consist of magnetic film deposited on an insulating base 34 and differentially biased by a graduated magnetic field provided by tapered pole-pieces 32, 33 of a permanent magnet 31. The pulsed magnetic drive field is applied to the elements 40 via a strip transmission line comprising conductive layers 36, 37 which are insulated from the elements 40 by insulating layers 38 and 34. To prevent reflections the line is terminated by its characteristic impedance. The magnetic elements 40 are linked by output winding 41 for detecting flux changes in response to the drive or read pulses. The windings 41, which may be deposited by printed circuit techniques, are wound oppositely around adjacent elements 40 so that extraneous flux linkages tend to cancel. Rectifiers may be used to obtain pulses of like polarity from all the elements in a group. Specification 679,730 is referred to.