Sweep circuit Oscilloscope history

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oscilloscope synchronized sweep. hor. selector sets horizontal frequency range (the capacitor); freq. vernier adjusts free-running frequency; sync. amplitude sets gain comparator.


early oscilloscopes used synchronized sawtooth waveform generator provide time axis. sawtooth made charging capacitor relatively constant current; create rising voltage. rising voltage fed horizontal deflection plates create sweep. rising voltage fed comparator; when capacitor reached level, capacitor discharged, trace return left, , capacitor (and sweep) start traverse. operator adjust charging current sawtooth generator have longer period multiple of vertical axis signal. example, when looking @ 1 khz sinewave (1 ms period), operator might adjust horizontal frequency little bit more 5 ms. when input signal absent, sweep free run @ frequency.


if input signal present, resulting display not stable @ horizontal sweep s free-running frequency because not submultiple of input (vertical axis) signal. fix that, sweep generator synchronized adding scaled version of input signal sweep generator s comparator. added signal cause comparator trip little earlier , synchronize input signal. operator adjust synch level; designs, operator choose polarity. sweep generator turn off (known blanking) beam during retrace.


the resulting horizontal sweep speed uncalibrated because sweep rate adjusted changing slope of sawtooth generator. time per division on display depended upon sweep s free-running frequency , horizontal gain control.


a synchronized sweep oscilloscope not display non-periodic signal because not synchronize sweep generator signal. horizontal circuits ac-coupled


triggered sweep

during world war ii, few oscilloscopes used radar development (and few laboratory oscilloscopes) had so-called driven sweeps. these sweep circuits remained dormant, crt beam cut off, until drive pulse external device unblanked crt , started constant-speed horizontal trace; calibrated speed permitted measurement of time intervals. when sweep complete, sweep circuit blanked crt (turned off beam), reset itself, , waited next drive pulse. dumont 248, commercially available oscilloscope produced in 1945, had feature.


oscilloscopes became more useful tool in 1946 when howard vollum , jack murdock introduced tektronix model 511 triggered-sweep oscilloscope. howard vollum had first seen technology in use in germany. triggered sweep has circuit develops driven sweep s drive pulse input signal.


triggering allows stationary display of repeating waveform, multiple repetitions of waveform drawn on same trace on phosphor screen. triggered sweep maintains calibration of sweep speed, making possible measure properties of waveform such frequency, phase, rise time, , others, not otherwise possible. furthermore, triggering can occur @ varying intervals, there no requirement input signal periodic.



triggered sweep controls on tektronix 465 oscilloscope


triggered-sweep oscilloscopes compare vertical deflection signal (or rate of change of signal) adjustable threshold, referred trigger level. well, trigger circuits recognize slope direction of vertical signal when crosses threshold—whether vertical signal positive-going or negative-going @ crossing. called trigger polarity. when vertical signal crosses set trigger level , in desired direction, trigger circuit unblanks crt , starts accurate linear sweep. after completion of horizontal sweep, next sweep occur when signal once again crosses threshold trigger.


variations in triggered-sweep oscilloscopes include models offered crts using long-persistence phosphors, such type p7. these oscilloscopes used applications horizontal trace speed slow, or there long delay between sweeps, provide persistent screen image. oscilloscopes without triggered sweep retro-fitted triggered sweep using solid-state circuit developed harry garland , roger melen in 1971.


as oscilloscopes have become more powerful on time, enhanced triggering options allow capture , display of more complex waveforms. example, trigger holdoff feature in modern oscilloscopes can used define period following trigger during oscilloscope not trigger again. makes easier establish stable view of waveform multiple edges otherwise cause trigger.








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