Ian Stirling writes: > Wolfgang S. Rupprecht wrote: >> Does a GSM/wifi/bluetooth/GPS phone really need >> 4 different RF chips and associated antennas and cabling? > There are a large number of reasons why not - firstly, 1GHz A/D > converter chips are both large, power-hungry, and expensive. > Secondly, processing the output from them is hard. > Thirdly, the dynamic range and intermodulation between different radio > frequencies mean that it's even harder.
One of the GPS manufacturers (Garmin) at one time described their system as a 1-bit A/D. Unfortunately they didn't say much more, so it wasn't clear if they mixed the raw 1.5 Ghz down and then "digitized" that or if they applied the A/D directly to the RF signal stream. In the GPS case, the further processing involves throwing the digitized signal at a large number of correlators and then look for a match with the candidate waveforms. The state of the art has progressed so much that one company SiRF, is now claiming to have the equivalent of 200,000 software correlators in their latest Sirf-III chip. So just thinking out loud, I wonder if it is strictly necessary to have an 8-bit A/D at Ghz frequencies. A much simpler one might be good enough. -wolfgang -- Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/ _______________________________________________ OpenMoko community mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/community
