Abstract: To solve the drawbacks of the existing HDB3(high density bipolar 3) encoders, such as high encoding complexity and long output delay,a fast design method for HDB3 encoders based on block encoding,unified polarity judgment and position polarity judgment was proposed.As a result,a fast design method for decoding was proposed based on polarity judgment to avoid checking substitute nodes in the process of decoding.Simulation results in QuartusⅡ 5.1 show that the proposed encoding and decoding methods have advantages over the existing methods in resource consumption and operation speed.Compared with the existing methods,with the proposed encoding and decoding methods the number of logic elements is dropped by 25% for encoding and 40% for decoding,and the fan-out numbers for encoding and decoding are decreased by 29.4% and 50.9% respectively.The test result indicates that the new encoder and decoder have a right function and can be applied to actual circuits.