Possible overflow of a video buffer verifier buffer employed in MPEG-like video encoders is prevented by controlling bits being drained from a video encoder buffer. In the method, the following steps are performed: forming a wiring and a filling layer filled between wirings, on a substrate; forming a gas permeable film on the wiring and the filling layer; removing the filling layer through the gas permeable film so as to form a gap between the wirings; filling a gas having a thermal conductivity equal to or higher than three times that of air at 0. The sensor chips may be arranged such that the pinned layers of the different chips are mutually anti-parallel to each other in order to form a push-pull bridge structure. To this end, the pre-charging circuit is connected to selectively pre-charge the data line to one or more of a plurality of voltage levels depending on the value of the digital video data signal.