The Nexus One currently being sold through Google, while only officially supporting the UMTS 3G frequency bands of 1,4 and 8 (2100Mhz, 1700Mhz-AWS and 900Mhz) carries the Qualcomm RTR6285 RF chip, which fully supports UMTS 3G frequency bands 1,2,3,4,5,6,8 and 9. These bands pretty much cover the whole world in case you were curious. In the US, AT&T utilizes bands 2 and 5 (1900 and 850), yep that’s in there. However, the Nexus One appears to be lacking one key feature to enable the AT&T bands, and that is the power amplifier chip, which takes the signal and boosts it enough to connect to and from the cell towers around you. Why is this?
Let’s start with a quick look at what is required to send/receive cell signals these days. I will refer to this group of components as the radio components of the cell phone and they consist of; antenna, power amplifiers and transceivers. As cell phones have become more complex over the years, so have the radio components.
The transceiver is kind of the brains of the radio components. It’s in charge of creating the signals to send and reading the signals received. It then sends the data to and from the main processor of your cell phone, which turns that into someone’s voice, the YouTube video you’re watching, or your latest email.
The power amplifiers are used to take the tiny signal coming from the transceiver and kicking it up a notch so that the signal is able to make it from your phone to the local cell tower. It’s the muscle of the radio components.
Finally, the antenna is what you think, a metallic cable/wire that is used to collect and send out the signal. In a cell phone, it’s usually very small and you can imagine it like a metal tape. Antennas need to be designed for the specific frequencies in order to get the maximum signal.
Nexus One support forums user, Sharkonwheels, pointed out that while ifixit.com was tearing through the Nexus One shortly after it’s launch, they uncovered the Qualcomm RTR6285 chip and after some quick searching, a PDF datasheet covering the RTR6285 shows the wide range of supported bands. The RTR6285 is the transceiver of the Nexus One. It handles all the data from the Snapdragon processor to the radio components, including GSM/GRPS/EDGE/WCDMA…that’s all the basic phone radio work, the 2G data work and the 3G data work. And, as mentioned previously in this post, it’s capable of most all the 3G frequency bands out there. It can understand them and speak their lingo right back.
However, the Nexus One has what appears to be 4 distinct power amplifiers.
Nexus One Power Amplifier Group
Two of the PAs are easily identifiable and datasheets for both are available. The other two, those marked A5001 and A5008 are not. As much as I tried searching I could not determine who makes them and exactly what they do, however, I am fairly confident that they are, in fact, PAs based on the package size and location on the board, as well as the fact that with just the first two identifiable PAs not all the officially supported 3G frequencies are accounted for.
The larger PA in orange is the Skyworks Sky77336 PA, which is a quad band GSM amplifier handling all the GSM PA work, which is the basic voice and 2G data. The next identifiable PA is also a Skyworks product, 77191. This is a single band WCDMA (3G DATA) amplifier and handles the 1700Mhz frequency used by T-Mobile.
My best estimate of the A5001 and A5008 must be that A5001 is a single band amplifier for the UMTS band 1, which is 2100Mhz, and the A5008 must be a single band amplifier for the UMTS band 8, which is 900Mhz.
Official Nexus One UMTS Frequencies are UMTS Band 1/4/8 (2100/1700/900).
Obviously, the antenna inside the Nexus One was designed for the frequencies listed, all of them, which include the basic voice and 2G data, as well as the 3G data, so in total that’s: 850, 900, 1700, 1800, 1900, 2100.
Being that those frequencies include all of AT&T’s network requirements too, meaning GSM/EDGE as well as the 3G frequencies of AT&T, the antenna inside the Nexus One is also compatible with AT&T.
The missing components seem to be the power amplifiers for AT&T’s 3G network.
So, did HTC/Google leave that out because it was too expensive to add an additional PA or two, making it a 6 chip design instead of 4? Probably not. Because there are many dual band PA IC chips available. If HTC/Google wanted to, for a very minimal price difference (talking a few dollars per phone at most), they could have used at least a couple dual band PAs to cover more 3G frequencies. Here in the US, to cover all the 3G possibilities, a phone would need to cover bands, 1, 2, 4, 5 and 8. Just looking at what Skyworks has available, Bands 1 & 8 can be covered with SKY77195, Bands 2 & 5 covered with SKY77196. Keep the same 77191 for Band 4 and you are done. That’s the same number of PAs, and I’m sure a dual band PA can’t be too much more expensive than a single band PA.
Also, the Nexus One isn’t the first phone capable of this “magic”. Other phones also have the RTR6285 chip.
Conspiracy
This brings me to my final point. I’d like to fist start by stating the obvious: I am no cell phone engineer. I know nothing about antennas, other than the little bit we covered in my physics courses. I’m not a designer, I don’t know the availability of the PA chips I mention above (77195 and 77196 seem new). Maybe there are technical reasons I am still not fully understanding. That being said, it seems to me that with very little effort HTC/Google could have made the Nexus One, and for that matter any manufacturer with any phone, can design it for use on many different networks. I’m typically not a conspiracy theorist, but in this case I’m leaning toward the idea that cell phones are built that way because the service providers, AT&T and T-Mobile, Verizon and Sprint, want it that way. Service providers love to get you on a contract with a subsidized phone. They more than get their money back and they keep a nice stable user base for at least 2 years. What about users who outright buy the phone? That’s ok with service providers too, just as long as the user still has to stay with them to get full functionality from the phone. T-Mobile only recently started to shift that a little, by offering the lower price plans for users with their own phone. This is a move in the right direction, allowing users independence from connecting a phone to a network. It’s like you purchase a car, that can only drive on certain highways. If you want to drive on a different highway, you have to buy a new car.
We’ve seen that it’s very likely AT&T will be getting their own version of the Nexus One via the FCC filings. So, it’s the same phone, just with different frequencies, which means a new set of drawings for HTC and new FCC filing, new paperwork etc…and the cost I’m sure of building a whole new phone verses just making one that works for both must be higher. The only reason to do this is so that the service providers are happy knowing that when someone purchases their Nexus One they are also purchasing their network and making the switch to another carrier is difficult.
I want to start a new website. www.mynexusoneforyournexusone.com Want to trade networks? Trade phones with other users.
