Patent GB-951398-A (GB)
Title: Sampling oscilloscopes
IPC: G01R13/34
Filed: 1960-08-09
Abstract: 951,398. Cathode ray oscillography. HEWLETT-PACKARD CO. Aug. 9, 1960 [Aug.10, 1959], No.27568/60. Heading G1U. [Also in Division H4] In a sampling cathode ray oscilloscope wherein the amplitude of a repetitive waveform is instantaneously measured at a selected point in time which is incrementally shifted along the time base at each successive recurrence, and the successive measurements are displayed as a series of luminous points of a cathode ray tube during the time occupied by a corresponding number of recurrent waveforms; the waveform under examination is applied to a sampling gate followed by an amplifier and a pulse lengthening circuit comprising a second gate and a signal storage circuit; a positive feedback circuit connecting the output of the pulse lengthening circuit and that of the sampling gate, a clamping circuit comprising a third gate connecting the amplifer output and the feedback circuit and a sweep circuit applying short sampling pulses to open the sampling gate and larger pulses to open the second gate and to lose the third gate respectively. An input waveform is applied to terminals 11, 13 of a sampling gate 15 comprising parallel pairs of series opposed diodes 17, 19 and 21, 23, normally held nonconducting by positive and negative bias voltages respectively connected to their junctions over resistors 25, 29, which possess an inter-electrode capacitance 34 across the output which is cathode follower coupled through A. C. amplifier 37 to a pulse lengthening circuit 41 comprising a further diode gate 43, normally held non- conducting by positive bias over resistor 49 and negative bias over resistor 53, which feeds an output storage capacitor 45, cathode follower coupled to the vertical plates of the display cathode ray tube. Positive feedback from the vertical plates over a resistance network incorporating the vertical shift potentiometer of the cathode ray tube is applied to the output of gate 15 and is adjusted to compensate the sampling efficiency of gate 15 for the time constant introduced by stray capacitance 34. A further gate 77 normally held open by positive and negative bias over resistors 83, 81 connects the vertical plates to the output of amplifier 37, and gating control is derived from sweep circuit 67 driving avalanche transistor pulse generator 69 applying short positive and negative sampling millimicrosecond pulses to gate 15, and also driving a blocking oscillator 21 generating microsecond pulses whose leading edges are synchronous with the sampling pulses, which are transformer coupled to gates 43 and 77. On pulsation gates 15 and 41 open and gate 77 closes, so that a sample of the waveform charges capacitor 45 to a corresponding voltage which vertically deflects the cathode ray tube, and a corresponding signal is fed back to the output of gate 15, which then closes, leaving gate 41 open and gate 77 closed until the termination of the larger pulse from blocking oscillator 71, when gate 41 closes and gate 77 opens to clamp the output of amplifier 37 to the voltage applied to the vertical plates. Specification 692,615 is referred to.