Patent GB-1087240-A (GB)
Title: Sampling oscilloscopes
IPC: G01R13/34
Filed: 1965-12-31
Abstract: 1,087,240. Cathode - ray oscilloscopes. VYZKUMNY USTAV MATEMATICKYCH STROJU. Dec. 31, 1965 [Dec. 31, 1964; May 3, 1965 (3)], No. 55370/65. Heading H4T. In a sampling oscilloscope for displaying a recurrent A.C. waveform, an adjustable sawtooth waveform and a brightening pulse waveform having positively going portions of the same duration as the adjusted sawtooth and both of the same period as the A.C. waveform are generated, all three waveforms are sampled at a rate different from the recurrence period of the waveforms and the samples, after stretching to increase their duration to just below the sampling period, are applied respectively, to the vertical deflection plates, the horizontal deflection plates and the brighteners control electrode of the display tube. Thus, in one embodiment (Fig. 1), the recurrent A.C. waveform (the portion to be displayed of which is assumed to comprise a narrow pulse of comparatively long repetition period) is applied to a gate 9 and a trigger pulse derived therefrom is applied to the (adjustable) sawtooth and brightening pulse generator 1 feeding respective gates 13, 20. Sampling pulses from a first output 6 of a free-running pulse generator 5 are applied to gate 9 and from a second output 7, delayed with respect to those from 6 by a time equal to the " inertia " of the sawtooth wave generator (i.e. the interval between the trigger pulse and the commencement of the linear portion of the sawtooth wave), to gates 13 and 20, the outputs of the three gates being fed to respective memory circuits 27, 28, 29 which feed their samples continuously (switch 39 in lower position as shown) to the vertical deflection plates 41, the horizontal deflection plates 42 and the brighteners control electrode 43 of the display tube 40 until terminated by a pulse from a third output 8 of generator 5 just before the occurrence of the next pulse from output 6. When the sampling rate is high relative to the period of the A.C. waveform, display of the narrow pulse portion to the exclusion of the remainder is ensured by supplying the lengthened samples from memory circuits 27 and 28- controlling the Y and X deflections respectively - to further memory circuits 45, 47 arranged to feed such samples continuously (switch 39 in upper position) to plates 41, 42 until the sequence of the next lengthened brightening pulse from memory 29 fed to auxiliary inputs 51, 51 (when new Y and X samples are fed to 45, 47). Because, in the particular case envisaged, a large number of Y and X samples not accompanied by brightening pulses are produced from portions of the A.C. waveform other than the desired narrow pulse portion, the desired samples in 45, 47 are rendered visible on the screen during the production of the former undesired samples by inverting the pulse output of memory 29-this being negative during the production of the undesired samples-in polarity inverter 49 and utilizing such inverted pulses as brightening pulses. This arrangement ensures that the trace brightness is independent of the relative portion of the complete A.C. waveform to be displayed. To prevent sampling of the desired portion more than once during each cycle of the complete waveform-e.g. if the desired portion is long with respect to the sampling period-a linkage (56, Fig. 2, not shown), operative when switch 39 is in the upper position, is arranged between sawtooth generator 1 and the sampling pulse generator 5 to adjust the period of the latter to be slightly longer than that of the selected for the sawtooth wave. A second arrangement for ensuring that only one sampling pulse occurs during the selected portion of the A.C. waveform involves the production of a pulse for the auxiliary inputs 50, 51 and as input to the polarity inverter 49 on the coincidence of the sawtooth wave from generator 1 with an auxiliary sawtooth wave of lower repetition frequency (Fig. 3, not shown). In a modification of the arrangements of Figs. 1 and 3, the generator 1 comprises two sawtooth generators, that triggered from terminal 2 being arranged to trigger the second sawtooth generator after an adjustable delay and either waveforms being supplied to terminal 3, selectively, by switch means (not shown) and the polarity inverter (49) is replaced by a further necessary circuit (70) feeding a gate (71) which inhibit the passage of brightening pulses (switch 39 in upper position) except in the absence of an input at its auxiliary control 77 (Figs. 5 and 6, not shown). This arrangement results in the relative delay of the two sawtooth waveforms being indicated by additional brightening of certain portions of the sampled trace. In all of the embodiments, the sawtooth input to gate (13) may be replacedby operation of switch 55-by a second recurrent A.C. waveform pen terminal (18) resulting in the display of sample traces representing comparative characteristics of selected portions of the two waveforms in the form of a fissajous patterns.