LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3
Preliminary
Design-In
Page 97 of 125
2.4.3
Antenna detection functionality
The internal antenna detect circuit is based on ADC measurement at
ANT
pin: the RF port is DC coupled to the
ADC unit in the baseband chip which injects a DC current (30 µA for 250 µs) on
ANT
and measures the resulting
DC voltage to evaluate the resistance from
ANT
pad to GND.
The antenna detection is performed by the measurement of the resistance from
ANT
pad to GND (DC element
of the GSM antenna), that is forced by the AT+UANTR command
:
refer to
u-blox AT Commands Manual
[2] for
more details on how to access to this feature.
To achieve good antenna detection functionality, use an RF antenna with built-in resistor from
ANT
signal to
GND, or implement an equivalent solution with a circuit between the antenna cable connection and the
radiating element as shown in Figure 55.
Antenna Assembly
Diagnostic Circuit
Application Board
LEON-G100/G200
ANT
ADC
Current
Source
RF
Choke
DC
Blocking
Front-End
RF Module
RF
Choke
DC
Blocking
Radiating
Element
Zo=50 Ohm
Resistor for
Diagnostic
Coaxial Antenna Cable
Internal
Resistor
Figure 55: Module Antenna Detection circuit and antenna with diagnostic resistor
Examples of components for the antenna detection diagnostic circuit are reported in the following table:
Description
Part Number - Manufacturer
DC Blocking Capacitor
Murata GRM1555C1H220JA01 or equivalent
RF Choke Inductor
Murata LQG15HS68NJ02, LQG15HH68NJ02 or equivalent
Resistor for Diagnostic
15k
Ω
5%, various Manufacturers
Table 32: Example of components for the antenna detection diagnostic circuit
The DC impedance at RF port for some antennas may be a DC open (e.g. linear monopole) or a DC short to
reference GND (e.g. PIFA antenna). For those antennas, without the diagnostic circuit Figure 55, the measured
DC resistance will be always on the extreme of measurement range (respectively open or short), and there will
be no mean to distinguish from defect on antenna path with similar characteristic (respectively: removal of linear
antenna or RF cable shorted to GND for PIFA antenna).
Furthermore, any other DC signal injected to the RF connection from
ANT
connector to radiating element will
alter the measurement and produce invalid results for antenna detection.
