GB1127744A - A method and system for clearing repetitive voltage waveforms of statistical interferences - Google Patents

Abstract

1,127,744. Pulse modulation systems. VARIAN INTERNATIONAL A.G. 29 Sept., 1965 [30 Sept., 1964], No. 41414/65. Heading H4L. In an apparatus for separating a recurrent voltage waveform from noise, of the type in which short sections of the signal are stored during a time interval and similar short sections are repeatedly added to the stored portion during succeeding time intervals, the voltage value is converted into a corresponding time spacing between pulse pairs prior to storage. Magnetic tape is used for the storage of the signals, and to prepare the apparatus, Fig. 1, it is first necessary to record control pulses by switching over switches 30, 31, 32 from the position shown. This starts oscillator 28 which generates pulses spaced by 400 ms. which trigger mono-stable devices 25, 26. Both outputs of device 26 are fed via a pulse shaper 27 to the recorder 11 (track I) so that a double pulse spaced by 1À5 ms. is recorded for each operation of device 26. This double pulse identifies the first pulse of the pulse pair. Monostable device 25 is adjustable to provide a delay of 4 to 8 ms. so that a pulse from device 25 is recorded, for example, 6 ms. after the double pulse from device 26. The pulse pairs are repeated every 400 ms. until track I on the endless magnetic tape has been completed. The output of the recorder 11 is then switched to feed the recorded pulses from track I via a shaper 12 to operate a mono-stable device 13, switches 30, 31, 32 being returned to the position shown. The first pulse of the double pulse triggers device 13 which applies one output to AND gate 14 and the second pulse of the double pulse causes gate 14 to put flip-flop 16 in its reset state whatever its previous state. One millisecond later the pulse from device 13 ends, the flip-flop 16 is set, and this triggers the monostable device 25. The device 25 returns to its original state after 6 ms. and mono-stable device 26 is operated to produce a double marker pulse, as described previously, which is recorded on the empty track II of the tape. When the second pulse of the pair is supplied from track I the device 13 is triggered, and 2À5 ms. later it is returned and resets flip-flop 16. This triggers a linear ramp voltage generator 19 which supplies a comparison voltage to a circuit 20 receiving also the input signal via amplifier 21. When the input signal and the comparison voltage reach equality an amplifier 23 applies a pulse via pulse shaper 27 to be recorded on track II. This cycle is repeated track-by-track until sufficient signal amplitudes have been added to enable the signal to be distinguished from the noise voltages which being random tend to cancel, the time spacing of the stored pulse pairs being increased in each cycle by the spacing of the new pulse pairs. When this is achieved the unit 33 is started and the recorded pulse pairs from track II are supplied via shaper 12, mono-stable device 13 and flip-flop 16 to the unit 33 for conversion back into amplitudes and application to a recording instrument. Transistorized circuitry is described, Fig. 3 (not shown). The apparatus may be included in a nuclear magnetic resonance spectrometer, Fig. 5 (not shown).