Interference power

Hi ,

one of the application note(APS004) DW1000 IC provide the value of maximum signal present at the in put of the DW1000 chip, Which is The strongest receiver signal presented to the DW1000 IC should not exceed -39 dBm. In my board there is one more radio its 1st harmonic is at 1.8 GHz and second 2.8 and 3rd 3.8 GHz. The radio transmit at +20 dBm power. The decawave antenna couples around 20 dB, 26 dB, 30 dB respectively for harmonics. we are working in the channel 5. If the coupled power at 2.98 GHz reaches more than -39 dBm , will it saturate the DW1000 IC.


Not clear what your question was, so I presume you are asking for help with handling the strength of the non UWB radio harmonics into the DW1000.

Decawave note in APS004 suggests they want the intended UWB receiver signal to not exceed -39 dBm, not necessarily that all signals must be less than -39 dBm, but it would be reasonable to limit those as well. The front end can only take so much signal before you saturate the either the analog or digital receiver chain.

The best approach to this based on your use case is a high pass filter (HPF) which cuts out the lower frequencies you don’t want entering the DW1000. These are commercially available.

In an LNA equipped node, the HPF can be after the antenna and before the LNA, or it can be after the LNA, each approach has benefits and drawbacks.

If the HPF is before the LNA, the filter keeps the LNA from being saturated and losing linearity. This makes the system more tolerant to interferers that are out of band (say cellular or 900 MHz, which sounds like your use case). The downside is that the insertion loss of the filter reduces reception range.

If the HPF is after the LNA, the filter doesn’t reduce reception range hardly at all, but you will be more susceptible to linearity limits on your LNA. This means a strong signal can saturate the LNA and causes loss of reception. We have seen this occur for nodes near cellular radio towers.

In our experience, putting the HPF before the LNA is the better solution which provides the most reliable system. The insertion loss can be under 1 dB and we find cutting out the low bands helps with reception reliability, so it has minimal impact on the system intended performance while greatly reducing interference from unwanted signals.

Another treatment is to use the non LNA RF path (the transmit path, typically) when you know in advance you have a very close transmitter you want to receive. To do this requires some sort of schedule knowledge of when and where particular nodes do transmit so you can preset the RF path. Typically any Aloha style (random beacon) type system doesn’t allow this, but air time scheduled/slotted systems do.

Mike Ciholas, President, Ciholas, Inc
3700 Bell Road, Newburgh, IN 47630 USA
+1 812 962 9408

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