SX1211I084TRT(2007) Просмотр технического описания (PDF) - Semtech Corporation

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SX1211I084TRT
(Rev.:2007)

Lowest Power Integrated UHF Transceiver Short Range Devices

Semtech Corporation 

SX1211

ADVANCED COMMUNICATIONS & SENSING

and Q amplifiers chains to provide the input signal to the FSK demodulator. Conversely, the OOK demodulator

derives its output from the RSSI block.

The overall accuracy of the RSSI is dependent upon both process and external components. So although the RSSI

resolution is 0.5 dB, its absolute accuracy is not expected to be better than +/-3 dB. Reliable absolute RSSI

measurement will require additional calibration.

3.4.7.2. Performance

The RSSI evaluates the signal strength by sampling I(t) and Q(t) signals 16 times in each Fdev period. An average

is then performed over a sliding window of 16 samples. Hence, the RSSI output register RXParam_RSSI is

updated 16 times in each Fdev period and outputs one correct value per Fdev. For accurate timing information on

the RSSI, please refer to Figure 49.

The dynamic range of the RSSI is over 70 dB, from the sensitivity level.

3.4.7.3. RSSI IRQ Source

The SX1211 can also be used to detect a RSSI level above a threshold. This function can be activated by bit

IRQParam_RSSI_irq, while the threshold level is selected by bits IRQParam_RSSI_thresh. This interrupt can be

mapped to the pins IRQ0 or IRQ1 by bits IRQParam_Rx_stby_irq0 or IRQParan_Rx_stby_irq1. The IRQ is

eventually cleared by writing a “1” to IRQ_Param_RSSI_irq.

The following figure shows the timing diagram of RSSI in interrupt mode.

IRQParam_RSSI_int

RXParam_RSSI(7:0)

24 26 27 30 25 20 20 20 18 22 33 20 22 34 33

IRQParam_RSSI_signal_detect

RSSI_irq

Clear interrupt

Figure 21: RSSI IRQ Timings

3.4.8. Fdev Setting in Receive Mode

The effect of the Fdev setting is different between FSK and OOK modes:

3.4.8.1. FSK Rx Mode

In FSK mode the Fdev setting has no impact on the circuit architecture. The user should leave it set to the default

value.

3.4.8.2. OOK Rx Mode

The frequency deviation Fdev, as described above, sets the sampling rate of the RSSI block. It is therefore

necessary to set Fdev to the recommended IF2 frequency of 100 kHz:

V3.0 – august 15th, 2007

Page 28 of 73

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