Low jitter design for ring oscillator in Serdes

A new configuration of delay cell used in voltage controlled oscillators is presented. Jitter comparison between source-coupled differential delay cell and the proposed voltage-controlled-oscillator configuration is given. Loop parameter based on low-jitter optimization in PLL is also introduced. A low-jitter 1.25 GHz SerDes is implemented in a 0.35 mum standard 2P3M CMOS process. The result shows that, RJ rms (random jitter) of high speed series output is 2.3 ps (0.0015UI) and RJ (1sigma) is 0.0035 UI. Phase noise measure shows -120 dBc/Hz at 100 kHz.