Patent GB-1282180-A (GB)
Title: A cathode ray oscilloscope apparatus
IPC: G01R13/32
Filed: 1970-04-03
Abstract: 1282180 Expanded timebase circuits; cathode ray tube circuits TEKTRONIX Inc 3 April 1970 [7 April 1969] 16010/70 Headings H3T and H4T A deflection waveform having two portions of different slope is produced by two independent time-base generators of adjustable slope, the second of which takes over when the first reaches a predetermined level and starts from the predetermined level. Fig. 1 comprises a slow sweep circuit A and a fast sweep circuit B of similar type including Miller type sweep generators 44, 74 and a quiescent level control circuit including the "sweep start amplifier" and the "disconnect circuit", the starting level of the "sweep start amplifier" of the B circuit being controlled via switch 90 from the output of the A sweep circuit so that the output level of the B sweep circuit, which is supplied through buffer 63 and horizontal amplifier 18 to the deflection plates, initially follows the A sweep and provides the first part of the deflection. When "delay comparator" 62 (in B) senses equality of the instantaneous A sweep value with an adjustable "delay time" value; provided by a potentiometer 64, the faster sweep is initiated and continues independently of the slower sweep to provide the deflection. Operation of sweep A is initiated by trigger circuit 36 which via a sweep gate controlling a "disconnect circuit" 40 which removes the feedback stabilization of the quiescent level and allows the sweep generator to commence operation. The resulting run down continues until the output fed via the sweep start amplifier to the reset multivibrator switches the multivibrator and reoperates the sweep gate and disconnect circuit to restore the quiescent level. The output from the sweep gate controls an unblanking circuit for the cathode-ray tube beam and also controls a hold-off circuit which maintains the reset multivibrator in its state long enough to ensure complete flyback. The reset circuit also through a lockout amplifier prevents reoperation of the B sweep circuit. This latter circuit operates similarly upon initiation by the delay comparator and provides unblanking signals both from the sweep gate and from an AND gate, the latter being necessary to blank out a step which occurs in the flyback. Fig. 2 shows the circuit of the B sweep generator. The Miller type sawtooth generator comprises valve 182 and transistor 184 with switchable timing capacitors 194 and timing resistors 196. The quiescent state is stabilized by applying the output from 74 to a circuit 220, 218 which compares the quiescent output with the reference voltage applied to the base of 218, this voltage being selectable as a fixed value or as the output from the A sweep generator. The collector of transistor 218 is connected to control the quiescent level through transistor 202. Triggering is effected when the A sweep input 42 reaches the adjustable level determined by potentiometer 64 whereupon the output of the comparator 96, 98 changes over a Schmitt trigger 110, 112 connected to its collectors. An output from this trigger controls a further trigger 140, 142 which when it changes over switches a tunnel diode 158 controlling a transistor 160 to render the stabilizing circuit transistor 202 ineffective so that the sweep can commence. The latter is applied through transistor 220 to the reset trigger 140, 142 so that when its level reaches a predetermined value this trigger changes over to reset the tunnel diode and allow the sweep to return to its quiescent value. The blanking circuit is controlled via transistor 240 by the output of the tunnel diode circuit and also via transistor 258 from the triggers 66 and 68. Further facilities.-The output transistor 272 may be connected to a "B + gate" operating an external circuit in coincidence with the sweep waveform. Ganged switches 216, 90, 254, and 260 provide for operation of the A sweep generator on its own or combined as herein before described, partial blanking to the A sweep so that only during the B sweep is the display complately unblanked, no difference in the deflecting speed of the beam occurring during the B sweep portion, and operation of the B sweep on its own delayed by the A sweep.