Hi,
I read the section 9.4 "Crystal" of the AN094 ("Using the CC1190 Front End with CC1101 under EN 300 220") and it says that some spurs derivated from the crystal oscillator can be a problem for certification :
"There are spurs appearing at N times the reference frequency (= N x crystal frequency/2).
These spurs are also folded around the carrier. The further away in Hz the spurs are from the
carrier the lower they will be in amplitude. For operation at 869.525 MHz the spur closest to
the carrier will be at 864 MHz when using a 27 MHz crystal and at 871 MHz when using a 26
MHz crystal. A 27 MHz crystal frequency is recommended for the CC1101-CC1190 design."
In order to confirm that point I made some measurements regarding the 7.8 "Unwanted emissions in the spurious domain":
- DUT: cc1101+cc1190 with SAW+integrated balun in between. RF filters equivalent to reference design "cc1101_cc1190EM 869MHz"
- cc1101 crystal frequency: 27 [MHz]
- method 7.8.2.1 (the module doesn't have any antenna, only a SMA connector)
- central frequency: 869.525 [MHz]
- nominal power: see pictures
- temperature: 23°c
It appears that the spur do not appear at 864 MHz but at 856.02 MHz:
I decided to decrease the power and see how the spurs are changing:
The spur at 883.02 MHz seem to be generated by saturation, as it disappears whenever I decrease the output power (it actually disappears under noise with an output power of ~15dBm).
Anyway, the spur at 856.02 MHz is inside the template with an output power of 9dBm or lower. Above 9dBm, it exceeds the template, and with the nominal 23dBm output power, in is 8dB too high. Furthermore, It is not on the 864 MHz frequency, as stated in AN094.
Could you please help me figuring out
1) why it is not on 864 MHz (given by the app note AN094)
2) how can I decrease this spur
ps: my register config:
0x29, // IOCFG2
0x2E, // IOCFG1
0x06, // IOCFG0
0x47, // FIFOTHR
0xD3, // SYNC1
0x91, // SYNC0
0xFF, // PKTLEN
0x04, // PKTCTRL1
0x45, // PKTCTRL0
0x00, // ADDR
0x00, // CHANNR
0x06, // FSCTRL1
0x00, // FSCTRL0
0x20, // FREQ2
0x34, // FREQ1
0x62, // FREQ0
0xCA, // MDMCFG4
0x75, // MDMCFG3
0x13, // MDMCFG2
0x22, // MDMCFG1
0xF8, // MDMCFG0
0x34, // DEVIATN
0x07, // MCSM2
0x30, // MCSM1
0x38, // MCSM0
0x16, // FOCCFG
0x6C, // BSCFG
0x43, // AGCCTRL2
0x40, // AGCCTRL1
0x91, // AGCCTRL0
0x87, // WOREVT1
0x6B, // WOREVT0
0xFB, // WORCTRL
0x56, // FREND1
0x10, // FREND0
0xE9, // FSCAL3
0x2A, // FSCAL2
0x00, // FSCAL1
0x1F, // FSCAL0
0x41, // RCCTRL1
0x00 // RCCTRL0
Thanks you.
