An 8-Gbps, Low-Jitter, Four-Channel Transmitter with a Fractional-Spaced Feed-Forward Equalizer

Abstract

An 8 gigabits per second (Gbps), low-jitter, four-channel transmitter with fractional-spaced feed-forward equalizer (FFE) is designed to meet the demand for broad transmission bandwidth in serial data communications. A novel frequency divider chain (FDC) architecture is developed, to satisfy the time requirements for high-speed data serialization. Moreover, a reconfigurable output driver circuit is employed to ensure compatibility with different protocols. In addition, a three-tap fractional-spaced FFE, which can enhance signal bandwidth significantly, is proposed, to compensate for channel loss. The transmitter was simulated and validated based on the Semiconductor Manufacturing International Corporation (SMIC) 55-nm process. The post-layout simulation results show the following: The tuning range of the phase-locked loop (PLL) can cover 1.6 to 4.6 GHz. At an output frequency of 4 GHz, the root-mean-square jitter (RJ) of the PLL after integration from phase noise was 1.93 ps. With an 8 Gbps output data rate, using the pseudo-random binary sequence (PRBS)-31 as a data source to simulate the whole transmitter, the power consumption values of the PLL and drive circuit were 27.0 and 29.2 mW, respectively, and the eye width and the valid eye height of output data were 0.76 unit interval (UI) and 0.68.