A 45nm SOI-CMOS dual-PLL processor clock system for multi-protocol I/O

As processors emerge with multiple wireline interfaces for high-performance digital media, a common multi-protocol clock system is essential for cost and power reduction. We present a 45nm SOI-CMOS system that clocks an 8-lane processor I/O designed for PCI Express®, DisplayPort, and TMDS. Its ring-VCO PLL (RO-PLL) achieves 0.99ps rms jitter that can be reduced further to 0.55ps upon switching to its auxiliary LC-VCO PLL (LC-PLL). As seen in Fig. 13.2.1, the clock system contains the two independent frequency synthesizers, an arrangement of programmable dividers to provide the required frequencies, and clock distribution circuitry. Furthermore, design-for-test features are embedded to correct for PVT variation for optimum jitter performance and to monitor PLL bandwidth and jitter peaking.