CC1120 Deviation vs Xtal accuracy

Jose Manuel Carballo

Hello.

I´m developing a system with this transceiver. I have configured the registers with Smart RF Studio, that I supposed that are values for a 10ppm xtal ("32MHz). My settings are for 868MHz, 50kbps, 2-GFSK, one of the predefined options of Smart RF Studio.

My question is, if I get a deviation of 25KHz for 10ppm xtal, can I use a 2ppm xtal to reduce the deviation and improve the sensitivity? Or it exists a limitation to reduce the deviation?

If its ok, can I use a 5KHz deviation for 2ppm?

Thanks for the answers

Jose

over 11 years ago

0 Sverre over 11 years ago

TI__Mastermind 39860 points

Theoretically, there is an optimum deviation/datarate setting if you simultaneously minimize the receiver filter bandwidth. Every halving of receiver filter bandwidth increases sensitivity with 3 dB whereas sensitivity vs deviation/datarate decreases with about 1.5-2.5 dB per halving down to a certain limit where the loss increases very fast.

Using a modulation index of 1 (m = 2 x deviation / symbol rate) is a good compromise if you set the RX filter BW wide just wide enough to account for the transmitted signal BW and the frequency error between RX and TX units.