This invention relates to a memory circuit for use in a video signal processing circuit and, more particularly, to an MOS-IC (metal oxide semiconductor-integrated circuit) memory circuit capable of frame-by-frame storage of a video signal, i.e., the so-called frame memory circuit.
The frame memory used for the frame-by-frame storage of the video signal is composed of several hundred chips of MOS-IC's each having 4,000-bit memory capacity. A substrate voltage (V.sub.SUB) as well as a main voltage (V.sub.DD) should be supplied to the MOS-IC. In this case, the main voltage should be impressed to the MOS-IC, after the substrate voltage is supplied thereto. In case the main voltage is impressed before the substrate voltage is supplied, the MOS-IC will be damaged and can no longer be used again. For this reason, a time sequentially operating switch has been required for a power source for a conventional system. When the power source is turned on, the time sequentially operating switch supplies the main voltage after the substrate voltage is supplied. When the power source is turned off, the switch cuts off the main voltage before the substrate voltage is cut off. However, even if the switch operates normally, the memory is damaged if the substrate voltage is lowered during the operation or is no longer supplied to the memory due to defective contact of a connector and the like. In addition, a conventional time sequentially operating switch having a combination of switches with relays is large in size.