STW82102B datasheet(53/67 Pages) STMICROELECTRONICS

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STW82102B

SPI digital interface

Doc ID 018516 Rev 2

53/67

10.4

Device calibration through the SPI interface

10.4.1

VCO calibration procedure (SPI interface)

The calibration of the VCO center frequency is activated by setting to ’1’ the SERCAL bit

(ST2 Register bit [6]).

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

procedure is required before every channel change:

Program the ST1 Register with the desired setting (DAC, Mixer, LO Control)

Program the ST3 Register with the desired setting (Functional mode, B and A counters)

Program the ST2 Register with the desired setting (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 1 MHz the following steps are needed:

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

frequency with a proper setting of R, B and A counter so that FPFD results lower than 1

MHz.

Once calibration is completed program the device with the proper setting for the desired

VCO and PFD frequencies according to the following steps:

Program the ST3 Register with the desired setting (Functional mode, B and A

counters)

Program the ST2 Register with the desired setting (R counter, VCO amplitude,

Charge Pump, Prescaler Modulus) with the SERCAL bit set to ’0’.

10.4.2

Power ON sequence (SPI interface)

At power-on the device is configured in power-down mode.

In order to guarantee correct setting of the internal circuitry after the power on, the following

steps must be followed:

Power up the device

Provide the reference clock

Implement the first programming sequence with a proper delay time between the ST3

and ST2 load rising edges (see Figure 24). The Tdelay value must respect the following

condition:

Fref is the reference clock frequency.

delay

1023

ref

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