- This paper presents a duo-binary circular turbo decoder based on border metric encoding. With the proposed method, the memory size for branch memory is reduced by half and the dummy calculation is removed at the cost of the small-sized memory which holds the encoded border metrics. Based on the proposed SISO decoder and the dedicated hardware interleaver, a duo-binary circular turbo decoder is designed for the WiMAX standard using a 0.13 μm CMOS process, which can support 24.26 Mbps at 200MHz.