STS1TX datasheet(31/70 Pages) STMICROELECTRONICS

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STS1TX

Block description

The STS1TX is provided with an automatic and very fast calibration procedure for the

frequency synthesizer. If not disabled, it is performed each time the SYNTH is required to

lock to the programmed RF channel frequency (i.e. from READY to LOCK/TX). Calibration

time is 54 µs.

After completion, the calibration word is used automatically by the STS1TX and is stored in

the RCO_VCO_CALIBR_OUT[1:0] registers.

In order to get the synthesizer locked when the calibration procedure is not enabled, the

correct calibration words to be used must be previously stored in the

RCO_VCO_CALIBR_IN[2:0] registers using VCO_CALIBR_TX field.

The advantage of performing an offline calibration is that the LOCK/setting time is roughly

20 µs (using proper VCO_CALIBR_TX register values).

It is recommended to set the T split time to the longest value (3.47 ns) to facilitate the

calibrator operation, SEL_TSPLIT field of the register SYNTH_CONFIG[0] (register address

0x9F) at 1.

If calibration is enabled, the LOCK/setting time is approximately 80 µs.

8.6

RCO: features and calibration

The STS1TX contains an ultra low-power RC oscillator capable of generating 34.7 kHz with

both 24 MHz and 26 MHz; the RC oscillator frequency is calibrated comparing it to the

digital domain clock fCLK divided by 692 or 750, respectively. The configuration bit, called

24_26MHz_SELECT in the ANA_FUNC_CONF register, contains the information of the

calibrator regarding the frequency of the crystal under operation. If the digital domain clock

is 25 MHz, the setting of the configuration bit 24_26MHz_SELECT will calibrate the low

power RC oscillator according to the following table:

817.0

827.7

100

827.7

838.3

101

838.3

849.2

110

849.2

860.2

111

860.2

872.0

000

872.0

883.8

001

883.8

895.8

010

908.0

919.8

100

919.8

932.0

101

932.0

943.8

110

943.8

956.0

111

Table 24. CP word look-up (continued)

Channel frequency

WCP [2:0]

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