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Two new lines of phase-locked loop (PLL) analog hard macros address issues associated with tradeoffs between undesirable options.

One series comprises low-jitter spread-spectrum PLLs, which allow spread-spectrum functionality to be included within an ASIC rather than on the system board, reducing manufacturing costs. These PLLs multiply an input clock by an integer or fixed-point number with a frequency spreading capability suited for PCs and other consumer applications.

A second series of PLLs includes low-bandwidth types that address excessive jitter from system clocks originating from lower-quality crystals. The PLLs generate high-speed clocks required for processors and chip interfaces that require low-jitter performance.

The spread-spectrum PLLs offer a completely adjustable bandwidth, spreading rate, and spreading amount. While the actual spreading amount with a particular setting can be difficult to control for most PLL designs, these circuits eliminate variability in the actual spreading amount.

Both PLL lines feature LockNow! technology, enabling them to achieve lock in essentially constant time at a particular output frequency independent of feedback divider and bandwidth settings. This is accomplished regardless of the loop bandwidth for a given output frequency and adds no additional frequency overshoot. ASIC and system-on-a-chip designers using PLLs with LockNow! technology can expect two or more orders of magnitude improvement in lock times with the same level of input period jitter rejection as before.

PLLs are available in a range of frequencies, multiplication factors, and functions for CMOS processes from 0.25 to 0.13 µm and foundries such as Texas Instruments, Taiwan Semiconductor Manufacturing Co., and UMC. PLL hard macros with LockNow! technology are available for a per-use license fee with no royalties.

True Circuits Inc.
(650) 691-2500

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