10: Applications and Hints
GPS/GLONASS Receiver Module A5100-A User Guide
42
Antenna Sensor with Current Limiter
”) works for Vcc from 3V to 5V. The antenna
current will be limited to 50 mA approximately.
If other transistors are used, other resistor values may be necessary as well. We
strongly recommend simulating and testing your realized version before using it.
10.10 TM_GPIO5 pin (1 pulse per second pin)
The 1PPS pin is an output pin.
In addition to precise positioning, GPS&GLONASS also allows for accurate timing
due to the synchronized atomic clocks in the GPS&GLONASS satellites. While the
current date and time is transmitted in NMEA sentences (UTC), an exact and accu-
rate timing signal is provided via the 1PPS pin of the
A5100
GPS&GLONASS re-
ceiver.
Under good signal conditions the 1PPS signal comes between 620ns and 710ns after
the full GPS&GLONASS system second which is accurately (around 10ns) synchro-
nized to UTC. Therefore the 1 second clock can be derived and maintained within
around 90ns under good signal conditions.
Note:
The 1PPS clock accuracy directly depends on the position accuracy!
The GPS&GLONASS signals travel at the speed of light, therefore a position inaccu-
racy directly translates into 1PPS inaccuracies.
10m po
sition deviation ≈ 33ns 1PPS deviation (typically)
100m position deviation ≈ 333ns 1PPS deviation (typically)
The NMEA messages containing absolute timing information (UTC time) are pro-
vided around 300ms after the 1PPS signal typically. This may change with the
GPS&GLONASS receiver setup.
The 1PPS signal is provided on a “as is” basis with no accuracy specification. It’s
NOT recommended to use 1PPS signal for accurate timing application.
