PCK12429

The internal oscillator PCK12429 uses the external quartz crystal as the basis f its frequency reference. The output of the reference oscillator isdivided by 16 before being sent to the phase detector.

The VCO output of PCK12429 is scaled by a divider that is configured by eitherthe serial or parallel interfaces. The output of this loop divider is alsoapplied to the phase detector.

The phase detector and loop filter of PCK12429 attempt to force the VCO outputfrequency to be M times the reference frequency by adjusting theVCO control voltage. Note that for some values of M (either too highor too low) the PLL will not achieve loop lock.

The output of the VCO is also passed through an output dividerbefore being sent to the PECL output driver. This output divider (Ndivider) of PCK12429  is configured through either the serial or the parallelinterfaces, and can provide one of four division ratios (1, 2, 4, or 8).This divider extends performance of the part while providing a 50%duty cycle.

The output driver of PCK12429 is driven differentially from the output divider, andis capable of driving a pair of transmission lines terminated in 50 Wto VCC2.0. The positive reference for the output driver and theinternal logic is separated from the power supply for thephase-locked loop to minimize noise induced jitter.

The configuration logic of PCK12429 has two sections: serial and parallel. Theparallel interface uses the values at the M[8:0] and N[1:0] inputs toconfigure the internal counters. Normally, on system reset, theP_LOAD input is held LOW until sometime after power becomesvalid. On the LOW-to-HIGH transition of P_LOAD, the parallel inputsare captured. The parallel interface has priority over the serialinterface. Internal pullup resistors are provided on the M[8:0] andN[1:0] inputs to reduce component count in the application of thechip.

The serial interface of PCK12429 centers on a fourteen bit shift register. The shiftregister shifts once per rising edge of the S_CLOCK input. Theserial input S_DATA must meet setup and hold timing as specified inthe AC Characteristics section of this document. The configurationlatches will capture the value of the shift register on the HIGH-to-LOW edge of the S_LOAD input. See the programmingsection for more information.

The TEST output of PCK12429 reflects various internal node values, and iscontrolled by the T[2:0] bits in the serial data stream. See theprogramming section for more information.