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Sweep Generator

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A traditional triangle-square wave generator is used for the sweep circuit.

 

Diode, D13, provides different timings for the forward sweep, and the retrace which can be faster than the forward sweep. Outputs are generated to tell the blanking circuit when to blank the CRT and when to unblank the CRT. The sync trigger input provides pulses that synchronize the start of the sweep to the voltage level selected by the user. The sync trigger input constantly retriggers a 74123 retriggerable one-shot so that pin 4 of U9 is always high. If synchronized trigger is not selected because the value of the input signal never reaches the selected sync level, then the retriggerable one-shot will time out allowing the sweep generator to free-run. A truth table for the 7476 is vital for analyzing this circuit and is given in the table below.

Inputs Outputs
Preset Clear Clock J K Q Q*
L H X X X H L
H H pulse L H L H

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Mike Ellis, 1999, All Rights Reserved