Patent GB-1269120-A (GB)
Title: Circuit arrangement, for use in triggering an (e.g. electron beam) oscilloscope
IPC: G01R13/28
Filed: 1969-10-24
Abstract: 1,269,120. Cathode-ray tube displays. SIEMENS A.G. 24 Oct., 1969 [28 Oct., 1968], No. 52310/69. Heading H4T. In an arrangement in which graphical representations of a plurality of signals are simultaneously displayed on a single-beam cathode-ray tube oscilloscope by switching the signals in sequence to deflection modulate a horizontal time base trace which is given different amounts of vertical displacement for each signal display the time base is triggered by a pulse derived from at least one of the signals and inhibition means are provided to prevent triggering by spurious pulses produced by the sequence switching means. The invention is described in connection with a system in which graphical representations of two signals are simultaneously displayed by switching each signal alternately to deflection modulate, during the whole of the sweep period, a respective one of two vertically displaced horizontal time-base traces initiated by trigger pulses derived from the respective signals when the time base sweep frequency exceeds 25 c.p.s. (termed " alternating " operation) or, when the latter is less than 25 c.p.s., by switching the two signals alternately at a high rate (1 Mc/s.) to deflection modulate the time base trace which, in this case, comprises a horizintal trace triggered by one of the signals and portions of which are vertically displaced during alternate modulation periods (termed " chopper " operation). Fig. 2 shows the arrangement for carrying out the invention and comprises a " chopper " consisting of an astable multivibrator CM operating at about 1 Mc/s. the pulse output of which operates, unless inhibited, to changeover the state of a bi-stable multivibrator FF which controls via switches U 2  and U 2 <SP>1</SP> the change-over between the input signals to be displayed MS1, MS2 and a delay line L1 feeding the vertical deflection amplifier. During " alternating " operation the negative portion of the beam blanking pulse (applied to K24 and differentiated by C10, R15) is effective to changeover the circuit FF and during this operation the " chopper " pulses are prevented from being effective by the application of negative potential via Zener diode ZD2 and resistor R9 which biases diode GR3 " off ". Thus during " alternating " operation the circuit FF switches the two input signals MS1, MS2 alternately to the vertical beam deflection amplifier via delay line L1 whilst simultaneously a synchronously operating trigger comprising a bi-stable multivibrator T operates via switches U1 and U 1 <SP>1</SP> to supply to the time base generator trigger pulses derived alternately from the signals MS1 and MS2. During " chopper " operation the circuit FF is changed over by the chopper output signals but the operation of multivibrator T is inhibited by supplying a negative potential to resistor R29 to bias a diode GR7 off. The signals MS1, MS2 are thus alternately switched to the vertical deflection amplifier at the chopper frequency and the time base is triggered by one or other of the signals depending on the state in which trigger T rests when diode GR7 is biased off. In this mode of operation spurious triggering of the time base is prevented by the biasing off of diode GR3 during the blanking period and a pulse derived over channel K21 from the chopper CM blanks the beam of the display tube during this period.