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This paper presents a multi-mode decoder design for Quasi-Cyclic LDPC codes for Mobile WiMAX system. This chip can be operated in 19 kinds of modes specified in Mobile WiMAX system, including block sizes of 576,..., 2304. There are four proposed design techniques: reordering of the base matrix, overlapped operations of main computational units, early termination strategy and multi-mode design strategy. Based on overlapped decoding mechanism, the decoding latency can be reduced to 68.75% of non-overlapped method, and the hardware utilization ratio can be enhanced from 50% to 75%. Besides, the proposed early termination strategy can dynamically adjust the number of iterations when dealing with communication channels of different SNR values. The proposed multi-mode LDPC decoder design is implemented and fabricated in TSMC 0.13 mum 1.2 V 1P8M CMOS technology. The maximum operating frequency is measured 83.3 MHz and the corresponding power dissipation is 52 mW. The core size is 4.45 mm2 and the die area only occupies 8.29 mm2.