High throughput pipelined LDPC decoder that supports multiple code rates and codeword sizes is proposed. In order to increase memory throughput, irregular block structured parity-check matrices are designed with the constraint of equally distributed odd and even nonzero block-columns in each horizontal layer for pre-determined set of code rates. Designed decoder achieves data throughput of approximately 1 Gb/s without sacrificing error-correcting performance of capacity-approaching irregular block codes. The prototype architecture is implemented on FPGA.