This article presents a 50–112-Gb/s current-mode four-level pulse amplitude modulation (PAM-4) transmitter with a two-tap fractional-spaced feed-forward equalizer (FFE). The principle analysis shows that the fractional-spaced FFE can provide an extended compensation range beyond the Nyquist frequency without amplifying noise. For the transmitter prototype implementation, the tap delay is adjusted by a coarse–fine capacitor array-based delay cell located in the quarter-rate clock path. Dynamic latches, pseudo-AND2s, and bandwidth-enhanced 4:1 multiplexers are employed to guarantee an adequate timing margin and a sufficient bandwidth for the data rate of 112 Gb/s. A linearity-optimized FFE driver is employed to overcome the current compression caused by the channel-length modulation. Fabricated in a 65-nm CMOS process, the measurement results show that the proposed fractional-spaced FFE can significantly improve the eye-opening in terms of expanding the eye width and optimizing the eyelid thickness. The PAM-4 transmitter can operate in both full-rate PAM-4 and half-rate NRZ modes, achieving a maximum data rate of 112 Gb/s with an energy efficiency of 2.17 pJ/bit.

中文翻译：

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50-112-Gb/s PAM-4 发射器，在 65-nm CMOS 中具有分数间隔 FFE

本文介绍了一种 50–112 Gb/s 电流模式四电平脉冲幅度调制 (PAM-4) 发射器，该发射器带有两个抽头分数间隔前馈均衡器 (FFE)。原理分析表明，分数间隔FFE可以在不放大噪声的情况下提供超出奈奎斯特频率的扩展补偿范围。对于发射器原型实现，抽头延迟由位于四分之一速率时钟路径中的基于粗-细电容器阵列的延迟单元进行调整。动态锁存器、伪与 2 和带宽增强型 4:1 多路复用器用于保证足够的时序余量和足够的带宽以实现 112 Gb/s 的数据速率。采用线性优化的 FFE 驱动器来克服由通道长度调制引起的电流压缩。采用 65 纳米 CMOS 工艺制造，测量结果表明，所提出的分数间隔FFE可以在扩大眼睛宽度和优化眼睑厚度方面显着改善眼睛睁开度。PAM-4 发射器可以在全速率 PAM-4 和半速率 NRZ 模式下运行，实现 112 Gb/s 的最大数据速率和 2.17 pJ/bit 的能效。