i want to do GPS 1 pps aligment clock signal generator. Clock signal should be at 24.576 Mhz and voltage level Vmax= 3.3 V and Vmin=0 V DC. How can i do that? It is very important to align between GPS PPS and Clock signal. While looking these components on the internet, i have found MAX24188 and DS31400. I am not familiar with these components. Is it possible to make this with Max24188 and DS31400? If yes can anyone explain me basicly how?
Electrical – GPS 1 PPS Aligment Clock Signal Generator
clockgpssynchronizationtiming-analysis
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The accuracy when following lines of longitude via GPS is easy enough to calculate. It's just a question of how much cross-track error you have relative to how long your baseline is (the distance you fly along the line of longitude).
Specifically, suppose you have a GPS receiver with an RMS error of 5m. This is in any direction, so it affects both the cross-track error and the length of your baseline. If you fly a nominal 100m north along a line of longitude as reported by the GPS, you'll have a cross-track error of up to 5m × √2 = 7m. (The √2 is applied because you have error in your start position, and error in your end position, too. These are assumed to be independent.) There will be a length error of up to 7m, too, but we can ignore that since its effect on the final answer is much less.
So, the overall error in your direction is up to 7m for the 100m you traveled, so the error in your concept of due north is \$\sin^{-1}\frac{7}{100}\$, or approximately 0.07 radians = 4.2° RMS.
Since the cross-track error remains constant regardless of the distance traveled, if you double the length of the baseline, the error in the angle will be halved, and so on. If you fly 500m north, then your error will be less than ±1°.
If you use an RTK-capable GPS receiver, the measurement error will be reduced by about two orders of magnitude — centimeters rather than meters. This would allow you to achieve much higher accuracy for a given baseline distance, or to use a shorter baseline for a given level of accuracy.
If your drone/UAV is large enough, you can mount two receivers on it and use a technique known as "short-baseline interferometry" to get an accurate heading measurement directly without any motion at all. The receivers need to be capable of giving you carrier phase measurements, and their antennas need to be on the order of 24" apart. One of my consulting clients has done pioneering work in this area.
Counting cycles between PPS pulses is not a good approach. Even using clocks with 10ppb stability, you still need to evaluate the skew between different units.
Using an integrated GPS Receiver with timestamping is a good approach. Note however that it will not be easy to get these 30ns RMS accuracy in real life conditions. 30ns translate to only 9m position accuracy. While most receivers reach this easily for kalman filtered position, you will see more disturbance to your timestamps (where the receiver cannot employ a hidden markov model) unless you also average over multiple events.
Multipath reception is your main adversary (for units some tens of km apart and events within fractions of a second). Multipath will be mitigated somehow by the receiver, but the best thing you can do is use a good antenna (choke ring or similar) and choose a good place. Putting it on a tripod can also help.
Group delay calibration will typically not be needed for 30ns if all your modules use a similar Setup (antenna cable length matters, also amplifiers or similar).
Far better accuracy can be reached if you are able to measure the event in band with the GPS Signals, that means trough the RF frontend of the reveiver. This will relate the timing directly to the received signals and offers the opportunity to cancel off several error sources. If you do not need the result in near real time, you may record GPS signals together with your trigger and postprocess them. This will give high accurary of relative position and time (differential GPS).
Best Answer
I have done this sort of thing several times in the past for several embedded systems, and it really isn't all that difficult. I typically use a COTS VCXO and an FPGA to implement the logic — nothing exotic.
First of all, what you really want to do is generate a "replica" 1 pps pulse using your 24.576 MHz clock. Then, you use feedback that varies the VCXO control voltage to phase-align this pulse with the reference pulse coming from the GPS receiver, which also means that your VCXO is then frequency-locked to the GPS timebase.
Use the replica pulse to drive the rest of your logic, rather than the reference pulse. The former, by definition, will be precisely phase-aligned with your local clock.
Just how precisely you need the rising edges of the two pulses to be aligned will ultimately determine how difficult this will be. Most GPS receivers provide a pulse that has on the order of ±50 ns error (jitter). Getting your replica pulse down to a similar level is really not all that difficult.