Synchronizing signal separating circuit separating synchronizing signal from a composite video signal

摘要

A synchronizing signal separating circuit inverts and amplifies, in an inverter 12, a composite video signal received from a video amplifying circuit 100 through a coupling condenser 1. An output node B of the inverter 12 is connected to an input node A of the inverter 12 through a switch 14 and a bias resistor 10. A bias resistor 11 is connected between the input node A and a ground potential. An output of the inverter 12 is further inverted and amplified by an inverter 13 and outputted as a composite synchronizing signal and also supplied to a control input of the switch 14. As a result, the switch 14 is turned on in a synchronizing signal period, so that the coupling condenser 1 is charged with the output of the inverter 12 and also the electric charges of the coupling condenser 1 are discharged through the bias resistor 11 in other period than the synchronizing signal period. Therefore, irrespective of a APL of an inputted composite video signal, it is possible to maintain a level difference between a top level of the synchronizing signal and a separation level to be constant to correctly perform separation of the synchronization.