Patent GB-1156761-A (GB)
Title: Signal Sampling System
IPC: G01R13/34
Filed: 1968-01-04
Abstract: 1,156,761. Cathode-ray tube displays. INTERNATIONAL BUSINESS MACHINES CORP. 4 Jan., 1968 [13 Jan., 1967], No. 627/68. Heading H4T. In a sampling system in which a cyclically recurrent waveform is sampled at different points so that over a number of cycles a replica of the waveform is reproduced, the sampling means operates to produce a plurality of samples of each point by sampling corresponding positions in each of a like plurality of successive cycles of the waveform. This method of operation is stated to improve the stability and accuracy of the system and further improvement is stated to result by changing the number of corresponding point samples taken inversely as the " Dot Weighting ". This latter factor approximates to the ratio of a given sample output to the difference between the input to the sampler and the value of the previous sample. The output of the sampling system may be displayed on a cathode ray tube and may also be fed to a computer via analogueto-digital converters, In Fig. 1, which shows an embodiment of the invention, the cyclically recurrent waveform is supplied at " Signal In " and from the leading edge of each cycle a trigger pulse is derived in trigger 10 and utilized to trigger a fast ramp generator 12 the output of which is fed to a comparator 14 also supplied with a staircase waveform from generator 16, the comparator operating on amplitude equality between the two inputs to produce an output pulse which controls a stroke generator 18 producing sampling pulses for sampling circuit 20 to which the recurrent waveform is supplied via a delay device 22 which compensates for the inherent operational delay in the circuit elements 10, 12, 14, &c. Thus, at each step of staircase generator 16 a succession of sampling pulses is produced which occur at corresponding periods during each cycle of the recurrent waveform and this period advances with each step of the generator 16 until a complete cycle of the recurrent waveform has been sampled. The number of sampling pulses produced at each step of staircase generator 16 varies inversely as the " dot weighting" and in the embodiment described provision is made for dot-weighting factors of 1.0, 0.75, 0.50 and 0.25 requiring 1, 2. 4 and 16 samples respectively. The dot-weighting is changed by manually operated means 24 comprising switch means for shunting the sampling circuit 20 with resistors of appropriate value (also Fig. 2, not shown) and this switch means is mechanically linked with further switch means in a counter control 26 which operates to vary the count in a counter 28 in accordance with the number of samples required by the selected dot-weighting (also Fig. 2, not shown). When such count has been reached counter 28 operates to step staircase generator 16 to the next step. This operation is illustrated in Fig. 4, which shows the last sample taken during period I, followed by four samples 1, 2, 3, 4 taken during period II and then the first sample taken during period III. The samples are supplied to the vertical amplifier 30 (Fig. 1) to deflect the beam of the display cathode ray tube 34, the horizontal deflection of which is provided by staircase generator 16 and horizontal amplifier 32. Fig. 4 shows the type of display produced except that in practice, the beam is only unblanked to display the last sample of the series taken during each step of the staircase generator. The output of the sampling system may also be fed to a digital computer by supplying the outputs of vertical amplifier 30 and horizontal amplifier 32 to Analogue-to-Digital (A/D) converters associated with the computer and the operation of which is initiated by the output of counter 28-" A/D convert initiate ". This output also controls the counter control 26 (Fig. 2, not shown) to arrest the operation until the sampling circuit has a stable output and then to hold the system at a particular point until the A/D conversion has been completed. The system then reverts to normal operation on receipt of an A/D conversion complete signal.