- Sun Mar 15, 2009 12:24 pm
#68511
Hi Randy;
There are several things to consider when evaluating RF ICs.
1) Output Power and Receive Sensitivity - These will govern the range you have
2) RX/TX Current - This is usually a typical value on the IC, but can change drastically depending on the quality of matching on your RF Path
4) harmonics - Different chips have different harmonics, if you need to pass compliance you need to know which will give you problems, especially if the chip happens to have a VCO that radiates at a frequency other than 2.4 GHz. Typically just using a transceiver chip and no external PA won't give you problems, though
4) Input/Output impedance - You ideally want 50 Ohm receiver impedance, and 50 Ohm output impedance (after a Balun, if the design is differential and calls for a balun (so differential load impedance will be different, but should be made into a standard 50 Ohms by the Balun))... Most ICs *SHould* have 50 ohms impedances, since it's a somewhat defacto standard, but I've designed with an IC that had ridiculous and arbitrary impedances... It made it very difficult to tune the circuit with matching networks.
5) Clocks - Can you drive the transceiver off the same crystal as other parts of the entire circuit (i.e. driving the radio from a micro-controller output clock) or will you need an additional clock circuit. This impacts cost and complexity
6) Data rates - Depending what you need to send, and how you want to send it, you may need additional overhead for error checking, retransmits, etc
7) Modulation type - Different radios transmit different ways, so once again you'll have to find out what you want to do, and in what kind of an RF environment. Some types of modulation are good for immunity to interference, others not.. Some allow you a lot of channels to hop on to hop around interferers in the band, others do not have that kind of diversity.. Complicated subject
8) Additional circuit requirements - What else will that particular radio IC require to run?
Those are just a few of the things to consider.. There are a bunch more that may or may not be important based on your requirements. I've designed with Chipcon/TI parts before, and like them, though I haven't had any experience with Nordic's offerings so can't say anything about them. I think in most applications, either could be a good choice, so it would really come down to what attribute of the particular chips is more import to your application. You could try to make sample RF links for your application using the dev kits you have, and use which ever one seems to work best for RF interference immunity, power, etc...
Last edited by Roko on Wed Mar 18, 2009 12:28 pm, edited 1 time in total.
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