STW81101 datasheet(33/42 Pages) STMICROELECTRONICS

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STW81101

SPI digital interface

33/42

6.4

VCO calibration procedure

The calibration of the VCO center frequency is activated by a '0' to '1' transition of the

SERCAL bit (ST1 Register bit[6]).

In order to program properly the device, ensuring the VCO calibration, the following

procedure is required before every channel change:

Program the ST1 Register with the desired settings (R counter, VCO amplitude,

Charge Pump, Prescaler Modulus) and SERCAL bit set to '0'

Program the ST2 Register with the desired settings (Functional mode, B and A

counters)

Program the ST1 Register with the desired settings (R counter, VCO amplitude,

Charge Pump, Prescaler Modulus) and SERCAL bit set to '1'

The maximum allowed PFD frequency (fPFD) to perform the calibration process is 1 MHz; if

the desired fPFD is higher than 1MHz the following steps are needed:

–

Perform all the steps of the calibration procedure programming the desired VCO

frequency with a proper setting of R, B and A counter so that fPFD is ≤ 1MHz.

–

Program the device with the proper setting for the desired VCO and PFD

frequencies according to the above step a) and b) only.

STW81101 Datasheet(PDF) 33 Page - STMicroelectronics