| 摘要 |
PROBLEM TO BE SOLVED: To stabilize the voltage of power being supplied when a video signal and power are transmitted on one and the same signal line. SOLUTION: The current of power being transmitted is so controlled by a variable constant current circuit 16 that it may be a predetermined target value. The line impedance can be kept high by the variable constant current circuit 16 and a camera-side constant current circuit 18, thereby overlaying a video signal and power can be overlaid. A low frequency component of the voltage of a signal line 10 is filtered by a low pass filter(LPF) 22. The output of the LPF 22 is compared with a given value by a voltage comparing circuit 24. When the LPF output is lower than the given value, the target value of the variable constant current circuit 16 is raised by a controlling circuit 26. When the LPF output exceeds the given value, the target value is lowered. By this method, a low frequency component of the voltage of the signal line 10 including a DC component can be kept at a constant value, and power of stable voltage can be supplied. |
