Patent GB-1006363-A (GB)
Title: Adaptive recognition method and system
IPC: G06F17/18
Filed: 1962-04-03
Abstract: 1,006,363. Correlation detection. GENERAL ELECTRIC CO. April 3, 1962 [April 21, 1961], No. 12751/62. Addition to 971109. Heading G1U. [Also in Division H3] A system for recognising recurring signals with increasing accuracy and capable of distinguishing recurring signals from random noise and other signals supplied by an input so that identification of recurring signals becomes more accurate, as claimed in Claim 1 of the parent Specification is modified by varying the weighting of the amplitude characteristics derived from subsequent inputs when a changing degree of correlation exists, as indicated by the successive comparison steps. An adaptive filter (Fig. 4) comprising a delay line 1 receiving successive input signals at 2 has cathode followers 3 spacedly tapped along it to provide an input for each of a series of multipliers 4 whose remaining inputs are cathode coupled from storage capacitors 5. Sampling capacitors 8 connected to the outputs of cathode followers 6 are coupled to respective capacitors 5 over diode bridges 12 normally biased to cut off but opened by a superimposed rectangular pulsetrain across diagonals 15,16 from a transistorised blocking oscillator and bias source 30 (Fig. 2). The outputs of the multipliers are summed over resistors 9 applied to a threshold circuit 10 operative when the sum (representing the cross correlation function between elements of the input) exceeds a given value to trigger the blocking oscillator and interconnect capacitors 8, 5 over the diode bridge. Initially the threshold is low and is progressively raised as capacitors 5 develop a more accurate representation of the input signal. The weight given to each sample signal of a series is represented by n/n+1<SP>k</SP> where n is the ratio of the storage to the sampling capacitor, and k is the number of times new information is inserted into storage, so that it is desirable for n to be initially small for rapid recognition of an unknown signal in presence of noise (e.g. in the interpretation of radar target signals) and subsequently large as the storage capacitors accumulate a better representation of the signal, so that individual samples are given less weight to discound surrounding noise. Fig. 3 shows the admittance characteristic of the diode bridge, and the combination of the blocking oscillator waveform and the standing bias varies the admittance of the bridge between the terminals 13, 14 in the conducting condition; the admittance value being controllable e.g. to point 29, by varying the bias Eb from source 28 (Fig. 2) or the collector voltage Ec of oscillator transistor 21. It is shown that, in general, for a sampling capacitor 8 and a storage capacitor 5, where Esj = voltage on capacitor 8; Eaj = voltage on capacitor 5 after j switch operations; Pj is weighting function after j operatory; so that since the weighting factor (1 - P) < 1, the effect of the last sampled signal voltage Esj upon the accumulated voltage Eaj is greater than that of the first sampled signal voltage E s . Bridges 12 are normally biased non-conducting from source 31, and when the cross-correlation circuit comprising multipliers 4, summation resistors 9 and threshold circuit 10 indicates high correlation between the input from terminal 2 and the stored signal on capacitors 5, the threshold circuit triggers pulse generator 30 to apply a switching pulse to the several bridges. A predetermined proportion of the total charge is exchanged between.the capacitors 8 and 5, in accordance with the bias from source 31, which is adjustable to determine the value of the weighting function (1 - P) which may be large at the commencement of a signal recognition period and small thereafter. The bias source 31 may be controlled by threshold circuit 10 to vary in proportion to the integrated threshold value, i.e. the integrated value of the cross correlation function which the summed multiplier signals must exceed before pulse generator 30 is triggered, so that P diminishes as the threshold value rises (Fig. 5 not shown). Control of the variable admittance devices may be obtained alternatively by variation of collector voltage Ec or the time period of the pulse generator.