V2.0 – Jan-13
User’s Manual
Page 37 of 41
10.8 VANT Pin
The VANT pin is an input pin.
The supply voltage for an active GPS antenna on the ANT input has to be fed into the
Vant pin. The easiest way to do that is to connect Vcc to VANT. The maximum cur-
rent is 50 mA.
Note
: Shortcut between ANT and GND may damage the A2100-A GPS receiver
module. This should be avoided by using an antenna current limiter.
The circuit (chapter “10.7.2 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.
10.9 TM_GPIO5 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 A2100 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.
10m position 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
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.
The given values are based on a 10 satellite, static GPS simulator scenario.
