Design Techniques for Signal Reflection Suppression in High-Speed 25-Gb/s Laser Drivers in CMOS

In this letter, we propose design techniques to suppress high-speed signal reflections observed in direct-modulated laser drivers. The first technique utilizes active back-termination (ABT) to absorb the reflected energy from the laser impedance mismatch. In the second design, capacitively coupled pre-emphasis (CCPE) is proposed to cancel the transient over-shooting observed from the bond-wire reflections. In order to evaluate these techniques, the two 25-Gb/s CMOS laser drivers are designed and fabricated in a standard 65-nm process. Experimental results show that both drivers exhibit clear 25.78-Gb/s optical eye-diagrams with >4 dB extinction ration, and also exhibit significant improvement in jitter performance when the ABT or CCPE is enabled.