Patent GB-893121-A (GB)
Title: Waveform recognition system
IPC: G06K9/00
Filed: 1960-04-21
Abstract: 893,121. Automatic character readings. GENERAL ELECTRIC CO. April 21, 1960 [May 1, 1959], No. 14009/60. Class 106 (1). In a character recognition system of the kind in which magnetic characters are sensed to produce a characteristic waveform to be sampled in a tapped delay-line and resistive correlation networks, one for each character, are connected to the tappings to recognise the waveform in the delay-line, the value of the resistors in each network is inversely proportional to the amplitude of the voltage expected at the corresponding tapping and directly proportional to the energy content of the corresponding waveform. Figs. 2 and 3 show the waveform derived from the sensing of characters " 6 " and " 7 " respectively. The delay line 15, Fig. 4, has nine tappings each connected to a transistor amplifier to give sample signals on terminals T1-T8 and T7¢. The terminal T7¢ provides a signal which is used in a synchronizing circuit in conjunction with that on terminal T8 to determine when the first peak is approaching the terminal T8 as shown in Figs. 2 and 3. An enabling signal is derived for application to the circuit which compares the outputs on the several correlation networks and produces an indication of which is the highest. The correlation network 20 for character " 6 " is connected to terminals T2, T3, T5, T6, T7 and T8. As shown in Fig. 2, terminals T1 and T4 are at zero volts when the " 6 " waveform is properly positioned in the delay line and these terminals can therefore be ignored. Terminals T3, T6 and T8 which have positive voltages are connected in a group through summing resistors R3, R6 and R8 to transistor amplifier Q21 and terminals T2, T5 and T7 which have negative voltages are connected in a second group through resistors R2, R5 and R7 to transistor amplifier Q23. The resistors are inversely proportional to the expected signal at the corresponding terminal in the usual way to provide a greater signal from the corresponding waveform than from any other. The amplifiers Q21, Q23 are connected to emitter-follower transistors Q22, Q24 having feed-back connections to the input terminals via resistors 123 and 127. The amplifiers are interconnected through a resistor 125 so that the positive samples on terminals T3, T6 and T8, which are summed and inverted in transistor Q21 are added to the summed negative samples as input to transistor Q23. The output on terminal 21 is proportional to the sum of the amplitudes of the positive and negative samples. To make the output of each correlation network, in response to its corresponding waveform, substantially constant, the resistors of each network are proportional, as a group to the energy content of the corresponding waveform. This is found for each waveform by summing the squares of all the signal samples and the corresponding scaling factor is applied to the resistors so that the signals from high energy waveforms are more attenuated than those from low energy waveforms. The signals from the terminals 21, 31, &c. are applied to peak detectors which store them on capacitors 129, 139, &c. The connection is through lowimpedance emitter-follower transistors Q41, Q42, Fig. 5, the outputs of which are clamped at a reference level through diodes 414, 424 until the monostable multivibrator 79 is triggered by the synchronizing circuit which, as mentioned above, detects when the waveform is properly positioned in the delay line. When the multivibrator 79 is triggered the voltage on terminal 21, 31, &c. is applied to the storage condenser 411, 421, &c. and applied to the comparator 43 which is made operative at the correct instant by a read-pulse generator operated slightly after the multivibrator 79. The read pulse generator 82 then provides a large positive pulse which cuts off transistor Q46 so that the potential on the common emitter line 460 changes in a negative direction and the transistor Q44, Q45, &c. connected to the largest signal will conduct before the others and the current drawn will hold the others at cut off. An output indicating the character will be present on terminals 50, 60 &c. Specification 796,579 is referred to.