Vincotech A1035-H, Руководство пользователя

Страница: 30 / 37

10.3 VANT Pin (antenna voltage input pin)
The VANT pin is an input pin.
The supply voltage for an active GPS antenna has to be fed into the VANT pin.
The easiest way to do that is to connect Vcc to VANT. The maximum current is 50
mA.
Note
: Shortcut between ANT and GND may damage the A1035-H GPS receiver
module. This should be avoided by using an antenna current limiter.
The circuit (chapter “
10.2.2 External Antenna Sensor with Current Limiter”) works
for Vcc from 3 V to 5 V. 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 completed version before using it.
10.4 1PPS Pin (1 pulse per second pin)
The 1PPS pin is an output pin.
In addition to precise positioning, GPS also allows for accurate timing due to the
synchronized atomic clocks in the GPS satellites. While the current date and time is
transmitted in NMEA sentences (UTC), an exact and accurate timing signal is pro-
vided via the 1PPS pin of the A1035-H GPS receiver.
Under good signal conditions the 1PPS signal comes between 620ns and 710ns
after the full GPS system second which is accurately (around 10ns) synchronized 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 signals travel at the speed of light, therefore a position inaccuracy directly
translates into 1PPS inaccuracies.
10 m position deviation
≈ 33 ns 1PPS deviation (typically)
100 m position deviation ≈ 333 ns 1PPS deviation (typically)
The NMEA messages containing absolute timing information (UTC time) are pro-
vided around 300 ms after the 1PPS signal, typically. This may change according to
the setup of the GPS receiver.
The 1PPS signal is provided on an “as is” basis with no accuracy specification.
The given values are based on a 10 satellites, static GPS simulator scenario.
V1.5 – Dec-09 User’s Manual Page 30 of 37