SYSTEM FOR DESCRAMBLING SCRAMBLED TELEVISION SIGNAL

摘要

PURPOSE:To prevent scrambled data from being easily descrambled by a person other than a specific contractor by extracting a synchronous(SYN) pattern signal during the period of a compressed vertical SYN signal and forming a horizontal SYN signal extracting window from the prescribed position of the extracted signal up to a position covering at least a horizontal SYN signal. CONSTITUTION:A SYN width information signal/SYN pattern information signal checking circuit is activated by a scrambling signal 1 and a horizontal SYN signal extracting window is generated from a horizontal SYN signal extracting window generating circuit (t1) 8 through a horizontal SYN signal extracting window position generating circuit 3 to execute descrambling operation. On the other hand, a descrambling signal is inputted to a horizontal SYN signal extraction detecting circuit 5 as an AND input together with an output from the circuit 3 to check whether a horizontal, SYN signal is or not. When the signal is not extracted yet, an output from the circuit 5 is inputted to the circuit 3 through circuits 6, 7 to determine the succeeding window position. The output of the circuit 5 is also inputted to a horizontal SYN timing signal generating circuit 9 and timing is generated from the circuit 9 and inputted to a horizontal SYN signal extracting window signal (t2) generating circuit to generate a signal (t2).