In this paper, a (1200,720) LDPC decoder based on an irregular parity check matrix is presented. For achieving higher chip density and less critical path delay, the proposed architecture features a new data reordering such that only one specific data bus exists between message memories and computational units. Moreover, the LDPC decoder can also process two different codewords concurrently to increase throughput and datapath efficiency. After chip implementation, a 3.33Gb/s data rate is achieved with 8 decoding iterations in the 21.23mm2 0.18μm silicon area. The other 0.13μm chip with the 10.24mm2 core can further reach a 5.92Gb/s data rate under 1.02V supply.