P1821

The P18xx is a versatile spread spectrum frequency modulator designed specifically for a wide range of input clock frequencies from 10 to 160 MHz (see Input Frequency and Modulation Rate Selections). The P18xx can generate an EMI reduced clock from crystal, ceramic resonator, or system clock. The P18xx-A to P18xx-H offer various combinations of spread options and percentage deviations (see Spread Deviation Selections). These combinations include Down Spread, Center Spread and percentage deviation range from ±0.625% to -3.50%.

The P18xx reduces electromagnetic interference (EMI) at the clock source, allowing a system wide EMI reduction for all the down stream clocks and data dependent signals. The P18xx allows significant system cost savings by reducing the number of circuit board layers, ferrite beads, shielding, and other passive components that are traditionally required to pass EMI regulations.

The P18xx modulates the output of a single PLL in order to "spread" the bandwidth of a synthesized clock, thereby decreasing the peak amplitudes of its harmonics. This results in significantly lower system EMI compared to the typical narrow band signal produced by oscillators and most clock generators. Lowering EMI by increasing a signal's bandwidth is called "spread spectrum clock generation".

The P18xx uses the most efficient and optimized modulation profile approved by the FCC and is implemented by using a proprietary all-digital method.