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

Fdev = IF 2 = 100kHz

MCParam _ Freq _ dev ="00000011"

3.4.9. FSK Demodulator

The FSK demodulator provides data polarity information, based on the relative phase of the input I and Q signals at

baseband. Its outputs can be fed to the Bit Synchronizer to recover the timing information. The user can also use

the raw, unsynchronized, output of the FSK demodulator in Continuous mode.

The FSK demodulator of the SX1211 operates most effectively for FSK signals with a modulation index greater

than or equal to two:

β = 2 * Fdev ≥ 2

BR

3.4.10. OOK Demodulator

The OOK demodulator performs a comparison of the RSSI output and a threshold. Three different threshold modes

are available, programmed through bits RXParam_OOK_thresh_type.

The recommended “Peak” threshold mode is described on Figure 22:

RSSI

(dB)

‘’Peak -6dB’’ Threshold

‘’Floor’’ threshold as in

MCParam_OOK_floor_thresh

Noise floor of

receiver

Zoom

Decay in dB as defined in

RXPAram_OOK_thresh_step

Fixed 6dB difference

Time

Period as defined in

RXParam_OOK_thresh_dec_period

Figure 22: OOK Demodulator Description

In peak threshold mode the comparison threshold used is the peak value of the RSSI, lowered by 6dB. In the

absence of an input signal or, equivalently, during the reception of a logical “0”, the acquired peak value is

decremented by one RXPAram_OOK_thresh_step every RXParam_OOK_thresh_dec_period.

When the RSSI output is null for a long time (for instance after a long string of “0” received, or if no transmitter is

present), the peak threshold level will continue falling until it reaches the “Floor Threshold” that is programmed

through the register MCParam_OOK_floor_thresh.

V3.0 – august 15th, 2007

Page 29 of 73

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