Patent GB-1217764-A (GB)
Title: Improvements in or relating to shift register arrangements
Inventor: MICHAELIS PAUL CHARLES
IPC: G11C19/08
Filed: 1968-05-16
Abstract: 1,217,764. Magnetic storage apparatus; automatic exchange equipment. WESTERN ELECTRIC CO. Inc. 16 May, 1968 [19 May, 1967], No. 23216/68. Headings H3B and H4K. In a shift register in which information is represented in a magnetic propagation medium in the form of single wall domains the propagation of the domains through the magnetic medium between input and output positions may: be inhibited. The shift register comprises two spaced anisotropic magnetic sheets 11a, 11b having a hard axis along the longitudinal axis, a domain in sheet 11b representing a zero and a domain in sheet 11a representing a one. In order to store a "1" a bipolar pulse is applied to input conductor 12 coupled to sheet 11a and to store a "0" a bipolar pulse is applied to conductors 14 coupling sheet 11b which pulses exceed the nucleation thresholds of the sheets. So as to prevent domains being nucleated in both sheets when one conductor is pulsed sheets 1 1a, 11b are provided with contiguous layers of aluminium or are abraded 30, 31 to raise the coercive force. The domains produced are spaced apart along the easy axis in the two sheets by an intermediate position coinciding with the forward path of conductor 17. In order to move the domains into the intermediate position a bipolar pulse is applied to conductor 17, the positive excursion of the pulse coinciding with the negative excursion of the pulse on the input conductors, with the result that a domain is first displaced along the easy axis to the intermediate position and then propergated along the forward path of conductors 17. To this end a chard axis bias field is supported by conductor Sb. In accordance with the invention an inhibit driver 21 normally maintains a current in conductor 20, positioned between the input and output conductor 22, to generate a field A counter to the propagation bias field and thereby inhibition gate the passage of domains due to the the absence of the propagation bias field. A domain D thus advances to the arrows A and stops and since the domains repel each other they form a queue. The effect of a domain in the sheet 11b is such as also to repel domains in sheet 11a so that as shown in Fig. 2 the spaces, representing a binary "O", in sheet 11a are maintained during the queuing. When the current in conductor 26 is pulsed off the domains are progressed to a read out position, by being first displaced along the easy axis to the output position coupled by output conductor 22 by conductors 24 and 17 in the manner described previously. The information may be read out optically by scanning the output position with a beam of polarized light. Each domain read out is erased by an easy direction field f e  supplied by a magnet or winding. The propagation rate may be increased at the output side of the inhibit conductor by an auxiliary field generated by coil Sb1.  The circuit of Fig. 1 may be used in a multifrequency - to - dial pulse converter which adapts pushbutton telephones to central offices which respond only to dial pulse inputs, the converter operating with a parallel input of binary "0"s and "1"s representative of a called decimal digit. A third magnetic sheet is provided to store and indication of an end of a digit Fig. 5 (not shown).  Single wall domains may be moved in a sheet which is isotropic in the plane of the sheet.