TELEVISION SIGNAL SYSTEM DISCRIMINATING CIRCUIT

PURPOSE:To easily discriminate the television signal system by comparing the width of a reference pulse with a vertical synchronizing signal obtained from latch of a high or low level of a composite synchronizing signal at a trailing edge of a pulse of nearly 20mus generated from the composite synchronizing signal. CONSTITUTION:Every time a composite synchronizing signal SYNC.IN is given to a negative logic input terminal of the 4th circuit, a monostable multivibrator MM 1 is driven, from which a pulse whose time constant is nearly 20mus depending on a resistor and a capacitor is generated. The 5th circuit FF 1 receives the signal SYNC.IN and an inverse of Q output of the MM 1 and latches the signal SYNC.IN depending whether it is at H or L level to detect a vertical synchronizing signal. A monostable multivibrator MM 2 of the 2nd circuit being triggered by the vertical synchronizing signal output a reference pulse and the FF 2 of the 3rd circuit compares the width of the latched vertical synchronizing signal with that of the reference pulse. Thus, the signal system is discriminated by a simple circuit.