hardware design v2.00

Smart Machine Smart Decision
5.2 GPS Power on/down Scenarios
5.2.1 Power on GPS engine
User can power on GPS engine by sending AT command “AT+CGPSPWR=1”.
5.2.2 Power down GPS engine
User can power down GPS engine by sending AT command “AT+CGPSPWR=0”.
5.3 GPS-VANT-OUT and GPS-VANT-IN
GPS-VANT-OUT is a 2.8V output for active external antenna, if the active external antenna works at 2.8V
voltage supply domain, user can connect the GPS-VANT-OUT and GPS-VANT-IN directly. If the antenna’s
power is not 2.8V, a proper voltage should be provided to the pin GPS-VANT-IN depending on the active antenna,
and the pin GPS-VANT-OUT should be kept open. For passive antennas, both the pin GPS-VANT-OUT and the
pin GPS-VANT-IN should be kept open.
5.4 GPS Antenna Interface
5.4.1 GPS Antenna Interface
The RF interface has an impedance of 50Ω. To suit the physical design of individual applications, SIM908 offers
alternatives
z Recommended approach: GPS RF connector
z GPS_ANT pad.
If the GPS antenna connector is used, the GPS_ANT pad should be left not connected, and the customer’s main
board under the GPS_ANT pad should be copper keep out.
To minimize the loss on the RF cable, it need be very careful to choose RF cable. SIMCom recommend the
insertion loss should be meet following requirements:
z GPS < 1dB
The customer’s GPS antenna also can be located in the customer’s main board and connect to module’s
GPS_ANT pad through microstrip line or other type RF trace which impendence must be controlled in 50Ω.
Figure 40: GPS antenna matching circuit
SIM908_Hardware Design_V2.00 2012.05.07
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