Single-Chip Low Cost Low Power RF-Transceiver (Rev. A)

CC2500Phase shifts are performed with a constanttransition time.The fraction of a symbol period used tochange the phase can be modified with theDEVIATN.DEVIATION_M setting. This isequivalent to changing the shaping of thesymbol.The MSK modulation format implemented inCC2500 inverts the sync word and datacompared to e.g. signal generators.16.3 Amplitude ModulationThe supported amplitude modulation On-OffKeying (OOK) simply turns on or off the PA tomodulate 1 and 0 respectively.17 Received Signal Qualifiers and Link Quality InformationCC2500 has several qualifiers that can be usedto increase the likelihood that a valid syncword is detected.17.1 Sync Word QualifierIf sync word detection in RX is enabled inregister MDMCFG2 the CC2500 will not startfilling the RX FIFO and perform the packetfiltering described in Section 15.3 before avalid sync word has been detected. The syncword qualifier mode is set byMDMCFG2.SYNC_MODE and is summarized inTable 24. Carrier sense in Table 24 isdescribed in Section 17.4.MDMCFG2.SYNC_MODESync word qualifier mode000 No preamble/sync001 15/16 sync word bits detected010 16/16 sync word bits detected011 30/32 sync word bits detected100 No preamble/sync, carrier senseabove threshold101 15/16 + carrier sense above threshold110 16/16 + carrier sense above threshold111 30/32 + carrier sense above thresholdTable 24: Sync word qualifier mode17.2 Preamble Quality Threshold (PQT)The Preamble Quality Threshold (PQT) syncwordqualifier adds the requirement that thereceived sync word must be preceded with apreamble with a quality above a programmedthreshold.Another use of the preamble quality thresholdis as a qualifier for the optional RX terminationtimer. See Section 19.7 on page 38 for details.The preamble quality estimator increases aninternal counter by one each time a bit isreceived that is different from the previous bit,and decreases the counter by 4 each time abit is received that is the same as the last bit.The counter saturates at 0 and 31. Thethreshold is configured with the register fieldPKTCTRL1.PQT. A threshold of 4·PQT for thiscounter is used to gate sync word detection.By setting the value to zero, the preamblequality qualifier of the sync word is disabled.A “Preamble Quality Reached” flag can alsobe observed on one of the GDO pins and inthe status register bitPKTSTATUS.PQT_REACHED. This flag assertswhen the received signal exceeds the PQT.17.3 RSSIThe RSSI value is an estimate of the signallevel in the chosen channel. This value isbased on the current gain setting in the RXchain and the measured signal level in thechannel.In RX mode, the RSSI value can be readcontinuously from the RSSI status registeruntil the demodulator detects a sync word(when sync word detection is enabled). At thatpoint the RSSI readout value is frozen until thenext time the chip enters the RX state. TheRSSI value is in dB with ½dB resolution. TheRSSI update rate depends on the receiverfilter bandwidth (BW channel defined in Section13) and AGCCTRL0.FILTER_LENGTH.fRSSI2 ⋅ BW=8⋅2channelFILTER _ LENGTHPRELIMINARY Data Sheet (Rev.1.2) SWRS040A Page 31 of 83