STS1TX datasheet(38/70 Pages) STMICROELECTRONICS

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Transmission and reception

STS1TX

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DocID025109 Rev 1

where:

•

FC_OFFSET is a 12-bit integer (expressed as 2's complement number) set by the

FC_OFFSET[1:0] registers

Furthermore, the selection between VCOH (“high”) and VCOL (“low”) in the frequency

synthesizer according to the band selected and the VCO threshold is required.

If the center frequency is below the frequency threshold for that frequency band, the VCO_L

must be selected by setting the bit 2 VCO_L_SEL field in the SYNTH_CONFIG register.

If the center frequency is above the frequency threshold for that frequency band, VCO_H

must be selected by setting the bit 1 VCO_ H _SEL field in the SYNTH_CONFIG register.

The user must make sure that actual frequency programming is inside the specified

frequency range. The accuracy of the offset is about 99 Hz for the 26 MHz reference and

about 198 Hz for the 52 MHz reference.

9.3

Modulation scheme

The following modulation formats are supported: 2-FSK, GFSK, MSK, OOK, and ASK. The

actual modulation format used is controlled by the MOD_TYPE field of the MOD0 register:

•

MOD_TYPE =

–

0 (00): 2-FSK

–

1 (01): GFSK

–

2 (10): ASK/OOK

–

3 (11): MSK

In 2-FSK and GFSK modes, the frequency deviation is controlled by the FDEV register

according to the following formula:

Equation 7

where:

•

fXO is the XTAL oscillator frequency (typically 26 MHz or 52 MHz).

•

FDEV_M is a 3-bit integer ranging from 0 to 7

•

FDEV_E is a 4-bit integer ranging from 0 to 9.

The fdev values obtainable are then:

For fXO = 52 MHz

Table 27. Frequency threshold

Frequency threshold for each band (MHz)(1)

1. By default, the VCO_H is selected.

Very low band

Low band

Middle band

High band

161281250

322562500

430083334

860166667

fdev

fxo

floor 8

(

FDEV_M

)

FDEV_E 1

–

)

⋅

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