Revision(s) Affected:

Description:

Digital filtering activity can potentially couple to XTAL pins and lead to spurs in the LO, which would also be seen in the Rx data. The spur in the Rx data would be seen at the spur frequency offset around a strong object. For example if the spur frequency is 500Khz and there is a strong object at 2Mhz , the Rx ADC spectrum could have a spike at 1.5Mhz or 2.5Mhz. Note that the Tx – Rx antenna coupling would also form a strong object close to DC. The spur frequency depends on the sampling rate (Fs). The strongest of these spurs have been observed when Fs is close to 10, 12.5, 18, 18.75,20, 25, Msps. In these ranges, an IF spur can appear at Fs-10 Mhz, 2Fs-40MHz, 4Fs-40 MHz, 4Fs-100 MHz, 8Fs-100 MHz , 2Fs-37.5 MHz, 2Fs-36 MHz. The spur is observable when the spur frequency falls within 1.5 MHz, beyond that it gets heavily filtered out. Please refer the device datasheet for max usable sampling rate.

Workaround(s):

Workaround #1:

Avoid sampling rates close to these numbers (10, 12.5, 18, 18.75, 20, 25 Msps) or use exactly these numbers (spur is at 0 Hz in the latter case).

Workaround #2:

Using external TCXO, instead of XTAL, with voltage swing between 1.4-1.8 Vpp can avoid these spurs.