INPUT SWITCH CIRCUIT HAVING NOISE REDUCTION FUNCTION AND VIDEO PRE-AMPLIFYING CIRCUIT HAVING VIDEO INPUT SELECTION FUNCTION

摘要

PURPOSE: An input switch circuit having noise reduction function and video pre-amplifying circuit having video input selection function are provided to prevent wrong operation caused by an instability of synchronous signal by eliminating noise contained in horizontal and vertical synchronous signals. CONSTITUTION: An input switch circuit comprises a horizontal synchronous signal switch unit(60) including a first comparing unit(80) having a first reference voltage setting portion for providing a first comparator with a lower voltage as a reference voltage if an output from the first comparator is high level, and a second comparing unit(82) having a second reference voltage setting portion for providing a second comparator with a lower voltage as a reference voltage if an output from the second comparator is high level; and a vertical synchronous signal switch unit(65) including a third comparing unit(84) having a third reference voltage setting portion for providing a third comparator with a lower voltage as a reference voltage if an output from the third comparator is high level, and a fourth comparing unit(86) having a fourth reference voltage setting portion for providing a fourth comparator with a lower voltage as a reference voltage if an output from the fourth comparator is high level.