gps
I just brought GPS module "Global-Top GMS-U1LP".
I want to setup it for its UART configuration.
In data-sheet there are 4 different ground but I am not able to trace which ground corresponds to which power input or for data.
Gms-u1lp dtatsheet
So with lot of doubt in mind I made following setup.
Is this configuration correct?
original setup according to data-sheet is as below:
Does anybody know how to setup this GPS receiver IC?
It looks pretty reasonable to me. I've got a question and a comment.
What are the components between the antenna and the GPS module? Any clocks etc? If they are power supply lines, it looks a little light on bypassing.
I'd also drop a dozen or so ground vias under the antenna itself, placed randomly. The reasoning behind this is to make sure you don't create a resonant cavity under the antenna, with the walls formed by ground planes top and bottom, as well as the via holes running around the outside. Unlikely, as your pcb is likely to be lossy, but you'd hate to hit the jackpot with that.
Note that the ANT1818B00DT1516A datasheet specifies a 50mm x 50mm ground plane underneath the patch antenna.
If the ground plane is larger or smaller then there will be effects on the overall performance of the antenna. You can read more in this Maxtenna application note. It states:
When the ground plane size changes the resonance frequency of the patch, where the matching is optimal, changes as well.
So if your ground plane is too small (or too large) the resonance frequency will change, essentially detuning it from 1575.42MHz and making it less sensitive.
In the graph below you can see the centre frequency varying by as much as 40Mhz when the ground plane is too small, the total bandwidth is also reduced. The gain is reduced by ~20dBic which can be seen in the application note.
Yes, this will work, but will also reduce the sensitivity. Ideally you want an unobstructed area around the antenna.
However, many commercial devices exist that have very densely packed enclosures, often with a screen on top. Consider the Garmin Nuvi below:
You will notice that there's not space for a large ground plane above the antenna and the screen is on the other side of the PCB. However, it's likely that a number of different patch antennas were tested before the devices were mass produced, so it's not directly comparable to your scenario.
If you want a small PCB then consider mounting the GPS antenna on the opposite side of the board to the screen. Allowing the correct size ground plane and test it. You might be surprised just how good the GPS receiver is.
No. The ground plane is for the GPS patch antenna only and is separate from the rest of your PCB. You should not connect it to any other part of your PCB.
As a separate note you should consider the antenna feed. It should be run on the opposite side of the PCB and ideally impedance matched to 50 ohms. This likely won't matter for a small run of hobby boards but might be important for a high performance system, because GPS runs at ~1.5Ghz which will likely be impacted on standard FR4 PCB.
Best Answer
All four pins are Ground, and all four pins should be connected to your circuit ground.
It may work if you leave some of the ground connections floating, but you may have reliability issues.
That GPS module does not have separate ground domains. Basically, to reduce the impedance of the ground connection, and possibly for reliability issues, they are using multiple connections from the same ground.
It is in-fact likely that if you use an ohmmeter to measure the resistance between she separate ground connections, you will find they are coupled together within the GPS module as well. You should still ground them all, however.