In the actual digital baseband communication system, in order to transmit information smoothly in the baseband, non-return to zero(NRZ) signal must be coded into code elements suitable for baseband transmission. Because the sender does not send clock information when sending, but in order to ensure the synchronization of the signal between the sender and the sender, it is necessary to extract clock information from the information stream at the receiver to recover the data. A novel encoding and decoding circuit for third-order high density bipolar code(HDB3) is proposed. The principle of all digital phase-locked loop(PLL) is used at the receiver. The decimal frequency divider is used to design a digital controlled oscillator(DCO) with loop filtering characteristics. Experiments show that the new HDB3 codec circuit can successfully recover timing information and data in the input signal frequency range of 2.048 MHz(±70 ppm).