CHARACTER SIGNAL SUPERPOSING CIRCUIT

• Main Author: MIYAJIMA AKIO
• Format: Patent
• Language: English
• Published: 16.10.1987
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; MULTIPLEX COMMUNICATION; PICTORIAL COMMUNICATION, e.g. TELEVISION

PURPOSE:To superpose a character signal without disturbing a horizontal scanning period by generating character signals synchronizing with synchronizing signals obtained from composite video signals and generating pulses shorter than horizontal scanning period synchronizing with above-mentioned synchronizing signals and superposing them on the composite video signals. CONSTITUTION:Synchronizing signals (b) obtained by removing video signals from composite video signals (a) by a video signal removing circuit 1 are inputted to a character signal generator 2 and character signals (c) are obtained. At the same time, synchronizing signals (b) are inputted to a monostable multivibrator 4 and an output pulse (e) having pulse width of period T'' shorter than horizontal scanning period T shown in the figure 3 synchronous with the synchronizing signals (b) is obtained. Then, character signals (f) and composite video signals (a) are superposed by a super=posing circuit 3 and composite video signals (g) on which character signals(f) are superposed are obtained. As pulse width of the output pulse (e) is determined by time constant of CR of the monostable multivibrator 4, the range of generation of character signals can be adjusted by changing time constant of CR.