STS1TX datasheet(32/70 Pages) STMICROELECTRONICS

32 / 70 page

Block description

STS1TX

32/70

DocID025109 Rev 1

By default, the calibration is disabled at reset to avoid using an out-of-range reference

frequency (for instance, when the XTAL is 26 MHz and the digital divider is active, in fact, by

default). After the internal clock divider is correctly configured, the user can enable the RCO

calibration in the PROTOCOL[2] register.

The user can replace the internal 34 kHz-signal source with an external one (provided

through a GPIO, Section 10.3). To enable the usage of the external signal, the user must set

the EXT_RCOSC bit in the XO_RCO_CONFIG register. However, the internal calibrator is

not automatically disabled from the EXT_RCOSC bit (the user must reset the

RCO_CALIBRATION bit in the PROTOCOL[2] register, if previously set).

8.6.1

RC oscillator calibration

RC oscillator calibration is enabled when bit RCO_CALIBRATION is set in the

PROTOCOL[2] register (by default the calibration is disabled). The calibration words found

by the calibration algorithm are accessible in the RCO_VCO_CALIBR_OUT[1:0] registers

(fields RWT_OUT[3:0] and RFB_OUT[4:0],).

When the calibration is disabled, the frequency of the RC oscillator is set by a couple of

configuration words, namely RWT_IN[3:0] and RFB_IN[4:0], in the

RCO_VCO_CALIBR_IN[2:0] registers (fields RWT_IN[3:0] and RFB_IN[4:0]). RWT_IN[3:0]

can range from 0 up to 13 (decimal value) affecting the raw value of the frequency, while the

more accurate and fine control is up to RFB_IN[4:0] (ranging from 1 up to 31).

8.7

Transmitter

The STS1TX contains an integrated PA capable of transmitting at output levels between -30

dBm to +11 dBm. The PA is single-ended and has a dedicated pin (TXOUT). The PA output

is ramped up and down to prevent unwanted spectral splatter. In TX mode the PA drives the

signal generated by the frequency synthesizer out to the antenna terminal. The output

power of the PA is programmable via SPI. Delivered power, as well as harmonic content,

depends on the external impedance seen by the PA. To obtain approval on ETSI EN 300

220, it is possible to program TX to send an unmodulated carrier.

The output stage is supplied from the SMPS through an external choke and is loaded with a

LC-type network which has the function of transforming the impedance of the antenna and

filter out the harmonics.

Table 25. RC calibrated speed

Digital domain clock

24_26MHz_SELECT

RC calibrated speed

24 MHz

34.7 kHz

26 MHz

34.7 kHz

25 MHz

36.1 kHz

25 MHz

33.3 kHz

STS1TX 数据表(PDF) 32 Page - STMicroelectronics

STS1TX 数据表(HTML) 32 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

数据表下载