A digitally controlled PLL for digital SOCs

A fully integrated digitally controlled PLL used as a clock multiplying circuit is designed and fabricated. The PLL has no off-chip components and it is made from standard cells found in most digital standard cell libraries. It is therefore portable between processes as an IP-block. Using a 0.35 μm standard CMOS process and a 3.0 V supply, the PLL has a frequency range of 152 MHz to 366 MHz and occupies an on-chip area of about 0.07 mm². In addition, the next version of this all-digital PLL is described in synthesizable VHDL-code, which simplifies digital system simulation and change of process. A new time-to-digital converter with simulated resolution of 250 ps is made for the next PLL.