Patent GB-730297-A (GB)
Title: Improvements in or relating to an electronic comparator for two numbers
IPC: G06F7/02
Filed: 1952-07-22
Abstract: 730,297. Digital electric calculating-apparatus. COMPAGNIE DES MACHINES BULL. July 22, 1952 [Sept. 24, 1951], No. 18515/52. Class 106 (1). An electronic comparator for comparing the values of integers N1 and N2 expressed as sums of integral components according to a given code and translated into electric pulse trains in which equal components of N1 and N2 are represented by two simultaneous pulses of same polarity, greater value components being represented by pulses produced later in time, comprises a memory for storing a circulating pulse comprising a pulse regenerator 4 connected in series with a delay line 6 and a gate 7, and two input paths, including pulse regenerators 18, 29, for respectively transmitting the pulse trains representative of N1 and N2 to the memory, each of which regenerators may deliver two pulses of opposite polarities on two opposed outputs in response to a pulse arriving at its input, two determined opposed outputs of regenerators 18, 29 being connected through a gate 20, 31 to the input 3 of regenerator 4 and the memory and through a buffer to an input of gate 7, so that two simultaneous pulses are blocked by gate 20, 31, a pulse of N2 unaccompanied by a pulse of N1 traverses this gate, and a pulse of N1 unaccompanied by a pulse of N2 closes gate 7 at a time when it can be reached by the pulse circulating in the memory. In the comparing device shown in Fig. 1, numbers N1, N2 to be compared are applied in series mode form (positive pulse for " 1, no pulse for " 0 ") to channels 1, 2. The numbers may be pure binary or, as particularly described, represented in coded decimal form with four digit periods (corresponding to 1, 2, 4, 8) for each decimal digit. The device consists primarily of rectifier gates, and the pulse regenerators 4, 18, 29. The regenerators 18, 29 receive the output of gates 11, 12 and 22, 23, which are normally opened to the input pulses on channels 1, 2 by earth potential applied, e.g. through a switch, to line 8, 9, 10. The comparison is effected as follows. If a pulse from N2 is unaccompanied by one from N1, a positive pulse from 29c is sent through gate 20, 31 to the input 3 of the memory loop circuit, the delays in 4 and 6 being such that a pulse circulates round the loop in a single digit period a. Pulses appearing simultaneously at 1, 2 produce no change; a negative pulse from 18d closes gate 20, 31, and a positive pulse from 29c applied to buffer gate 34, 63 prevents this negative pulse from lowering the potential applied to rectifier 7a. If a pulse from N1 is unaccompanied by one from N2, however, the potential applied to 7a is lowered so that gate 7 is closed to cancel any pulse circulating in the loop. Thus, if N2 is greater than N1, but not otherwise, a pulse will remain in the loop at the end of the comparison. Such a pulse is passed from 5 through output gate 75 and the loop is cleared by applying a negative impulse to line 64 and rectifier 7c. The device may be employed also for comparing successive decimal digits of a number N3, applied to channel 66, with " 1 " which is represented by an impulse on channel 65 at the beginning of each decimal period. Earth potential is then applied to line 67-70, instead of 8, 9, 10, thus opening gates 69, 70 and 71, 72; gate 75 is opened at the end of each decimal period (consisting of 4 periods a) and an output pulse passed therethrough means that a digit of N3 is zero. Each pulse at 65 produces a negative pulse at 29d which, due to the negative potential now applied from line 8, 9, 10 to rectifier 41, lowers the potential applied to rectifier 7b to cancel any pulse circulating in the loop at the end of a previous decimal period. The comparing device may be used in punchedcard accounting-machines. Pulse regenerators. Each regenerator (Fig. 2, not shown) is similar to the pulse reshaper described in Specification 711,240 and comprises a pentode having regular negative digit pulses U1, Fig. 4, applied to its cathode from line 19, 18b, 29b, and positive attenuated pulses U2 applied to its control grid; each pulse U2 causes regenerated pulses, coincident with U1, to be sent through an output transformer to raise and lower the potentials of upper and lower terminals, such as 29c, 29d (when provided), from negative and earth resting levels respectively. Specification 711,240, [Group XXXIX], is referred to.