AMY-6M - Hardware Integration Manual
UBX-17021971 – R07
Design-in
Page 27 of 57
2.7
RF input
The AMY-6M RF input is already matched to 50 Ohms and has an internal DC block, see Figure 1. To achieve the
performance values as written in
AMY-6M Data Sheet
[1] an active antenna with a good LNA inside or the
mandatory LNA in front of AMY-6M must have below 1dB noise figure.
2.7.1
Active Antenna used
In case an active antenna is used, just the active antenna supply circuit has to be added in front of AMY-6M RF-
input. See section 2.1.11. In case the active antenna has to be supervised, the Active Antenna Supervisor circuit,
see section 2.8, has to be added to the active antenna circuit. This Active Antenna Supervisor circuit also makes
sure the active antenna is turned off in some Power Save Mode stages.
2.7.2
Passive Antenna
In case no active antenna is connected to the AMY-6M it is mandatory to use an additional LNA in front of
AMY-6M. An LNA (LNA1) alone would make the AMY-6M more sensitive to outband jammers, so an additional
GPS SAW filter (F2) has to be connected between the external LNA (LNA1) and the AMY-6M RF-input.
Figure 23: Recommended passive antenna design
PIO17 can be configured as ANTOFF (active antenna off) signal which can be used to turn off an external LNA.
The ANTOFF signal must be inverted for common LNAs which come with an enable pin which has be “low” to
turn off. To configure PIO17 as ANTOFF, see
u-blox 6 Receiver Description including Protocol Specification
2.7.3
Increased Jamming Immunity
If strong outband jammers are close to the GPS antenna (e.g. a GSM antenna) GPS performance can be
decreased or the maximum input power of the AMY-6M RF-input can be exceeded. An additional SAW filter has
to put in front of the external LNA (LNA1). If the external LNA (LNA1) can accept the maximum input power, the
SAW filter between the passive antenna and external LNA (LNA1) might not be necessary. This results in a better
noise figure than an additional SAW filter in front of the external LNA (LNA1).
Figure 24: Recommended circuit for increased jamming immunity
