Hi,
I have a couple questions about the RX PLL in the LMS chip:
- What are the various LOBUF for ? (1/2/3). Do they correspond the the 3 input of the RX side ? I see they're controlled by the SELOUT bits, but I have no idea how to choose. Should it be matched to LNASEL_RXFE ?
- What's the expected levels of the LO harmonics ? In my tests I see to measure around -10 dB for 3xLO and ~ -22 dB for 5x LO. Is there any way to improve this ?
The method I used to measure is to feed 400 MHz narrow bw signal to the input. Tune LMS to 400 MHz and measure the received strength, then change the signal generator to TX a signal at 1.2 GHz and measure again, then at 2GHz, and so on ...
Cheers,
Sylvain
Hi Ricardas,
Thanks for the quick answer. A couple of followup questions :
You should see 2xLO, 4xLO ... as well.
Oh really ? Mmm, I couldn't see those. I guess they're much lower than the odd harmonics and were buried in the noise floor.
On the TX side these can be reduced by RF filter/duplexer. RX LPF will filter them out on the RX side.
Yes, I know how to get rid of them. Unfortunately designing a front end that can programmably filter those for the whole range of the LMS (like in a broadband SDR), it's not easy :p
So I was wondering if you had any data on the typical / worst case values for those so I can know exactly how good a pre-filtering I need to have on the input.
Cheers,
Sylvain
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Sylvain Munaut