SSC - Spread Spectrum Clocking 扩频时钟技术主要是用来降低EMI。
CC - Common Clocked architectures (CC)
SRIS - Separate Refclk Independent SSC.
SRNS - Separate Refclk with No SSC。
SRNS允许600ppm,而SRIS允许5600ppm(其中SSC允许5000ppm(单向展频0.5%,0.5/100=0.005*100 0000ppm=5000ppm),TX/RX允许600ppm)
如果使用SSC所有使用SSC芯片的时钟必须同源
如果不使用SSC,各芯片的时钟不要求同源
PPM计算方法:
ppm是百万分之一,我用的晶振是74.25MHz,实际用频率计测量是74.24MHz,晶振的误差是(74.24-74.25)/74.25≈0.000135=135*10^-6
误差是135ppm
HBW_BYPASS_LBW
In PLL bypass mode, the input clock is passed directly to the output stage, which may result in up to 50 ps of additive
cycle-to-cycle jitter (50 ps + input jitter) on the differential outputs.