From ASICs to SOCs: A Practical Approach

Appendix C. Phase-Locked Loops (PLLs)

Most ASICs currently developed include one or more phase-locked loop (PLL) circuits. PLLs are used for a number of reasons including reduction of on-chip clock latency, synchronization of clocks between different ASICs, frequency synthesis, and clock-frequency multiplication. ASIC vendors offer various types of PLLs based on their frequency range, pin count, size, and stability.