The Design Of Coder Circuit In Magnetic Card Decoder Chip

Based on SPM2200 magnetic card decoder chip's characteristic and application, the paper researches on the system structure of the chip, and designs the coder circuit of this chip which mainly sees to transform analog voltage signals into binary F2F signals. The capability of coder circuit module is related to the performance of dealing with low frequency small signals of the chip, so this module is one of the necessary and important modules of SPM2200 magnetic card decoder chip.In this paper , according to the characteristic,application and performance of SPM2200 , we put forward a new structure .This structure , unlike other circuits which have an invariable benchmark , its benchmark is changed with the input signals . This structure can overcome the jam of glitch for low frequency small signals effectively. At the same time, the structure can also improve coding efficiency, and reduce error rate in coding and the difficulty of decoder's design; and the structure of circuit is compaction, which can reduce the area of chip, and depress the cost of fabrication.Based on CSMC0.5um CMOS technology, using EDA software, we simulate the performance of this module. The result proved that the performance achieved the request of the design. Consequently, we completed layout design according to CSMC0.5um CMOS technology. During our design, we used common-centroid layout for some important circuit, and used guard ring to isolate sensitive circuit against bulk noise made by other circuit. Also, we used"digital ground"and"analog ground"so as to avoid instantaneous noise created by digital circuit to interfere analog circuit. For some sensitive signal line, we shielded them.At last, the design was taped out. And the sample was tested. The test results proved that if we moved the card at the speed of 10cm/S (signal frequency is about 200Hz), the chip worked wonderful and fulfilled the request of the design.