STW81103 datasheet(40/53 Pages) STMICROELECTRONICS

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SPI digital interface

STW81103

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The LO output frequency is programmed by setting the proper value for A, B and R

according to the following formula:

and P is the selected prescaler modulus.

7.3.1

Default configuration

At power on, all the bits are set to '0'. Consequently the part starts in power down mode.

7.4

VCO calibration procedure

Calibration of the VCO center frequency is activated when the SERCAL bit (ST1 register

bit[6]) is set to 1.

To program the device properly while ensuring VCO calibration, perform the following steps

before every channel change:

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 with the SERCAL bit set to 1.

The maximum allowed PFD frequency (F

PFD) during calibration is 1 MHz; if you want a FPFD

higher than 1 MHz, perform the following additional steps:

●

Perform all the steps (step 1 and 2 above) of the calibration procedure, making sure to

program the desired VCO frequency with proper settings of the R, B and A counters so

that F

PFD is

≤1 MHz.

●

Program the device with the desired VCO and PFD frequency settings as per steps 1

and 2 above with SERCAL bit set to 0.

7.4.1

VCO calibration auto-restart feature

The VCO calibration auto-restart feature can be enabled in two steps:

Set the desired frequency ensuring VCO calibration as described above (

Section 7.4)

Program the ST2 register with the CAL_AUTOSTART_EN bit set to '1' while keeping

unchanged the others.

where

DR equals

{

for direct output

0.5

for output divided by 2

0.25 for output divided by 4

OUT

()

REF

CLK

–

-----------------------------------

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