u-blox SARA-R4 Series, System Integration Manual

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SARA-R4 series - System Integration Manual
UBX-16029218 - R06 Design-in
Page 56 of 102
2.4.2 Antenna detection interface (ANT_DET)
2.4.2.1 Guidelines for ANT_DET circuit design
Figure 24 and Table 20 describe the recommended schematic / components for the antenna detection circuit
that must be provided on the application board and for the diagnostic circuit that must be provided on the
antenna’s assembly to achieve primary and secondary antenna detection functionality.
Application Board
Antenna Cable
SARA-R4 series
56 ANT
62
ANT_DET
R1
C1 D1
L1
C2
J1
Z
0
= 50 Ω Z
0
= 50 Ω
Z
0
= 50 ohm
Antenna Assembly
R2
C4
L3
Radiating
Element
Diagnostic
Circuit
GND
L2
C3
Figure 24: Suggested schematic for antenna detection circuit on application board and diagnostic circuit on antenna assembly
Reference Description Part Number - Manufacturer
C1 27 pF Capacitor Ceramic C0G 0402 5% 50 V GRM1555C1H270J - Murata
C2 33 pF Capacitor Ceramic C0G 0402 5% 50 V GRM1555C1H330J - Murata
D1 Very Low Capacitance ESD Protection PESD0402-140 - Tyco Electronics
L1 68 nH Multilayer Inductor 0402 (SRF ~1 GHz) LQG15HS68NJ02 - Murata
R1
10 k

Resistor 0402 1% 0.063 W
RK73H1ETTP1002F - KOA Speer
J1
SMA Connector 50

Through Hole Jack
SMA6251A1-3GT50G-50 - Amphenol
C3 15 pF Capacitor Ceramic C0G 0402 5% 50 V GRM1555C1H150J - Murata
L2 39 nH Multilayer Inductor 0402 (SRF ~1 GHz) LQG15HN39NJ02 - Murata
C4 22 pF Capacitor Ceramic C0G 0402 5% 25 V GRM1555C1H220J - Murata
L3 68 nH Multilayer Inductor 0402 (SRF ~1 GHz) LQG15HS68NJ02 - Murata
R2
15 k

Resistor for Diagnostic
Various Manufacturers
Table 20: Suggested components for antenna detection circuit on application board and diagnostic circuit on antennas assembly
The antenna detection circuit and diagnostic circuit suggested in Figure 24 and Table 20 are here explained:

When antenna detection is forced by the +UANTR AT command, the ANT_DET pin generates a DC current
measuring the resistance (R2) from the antenna connector (J1) provided on the application board to GND.

DC blocking capacitors are needed at the
ANT
pin (C2) and at the antenna radiating element (C4) to
decouple the DC current generated by the ANT_DET pin.

Choke inductors with a Self Resonance Frequency (SRF) in the range of 1 GHz are needed in series at the
ANT_DET pin (L1) and in series at the diagnostic resistor (L3), to avoid a reduction of the RF performance of
the system, improving the RF isolation of the load resistor.

Resistor on the ANT_DET path (R1) is needed for accurate measurements through the +UANTR AT
command. It also acts as an ESD protection.

Additional components (C1 and D1 in Figure 24) are needed at the ANT_DET pin as ESD protection.

Additional high pass filter (C3 and L2 in Figure 24) is provided at the
ANT
pin as ESD immunity improvement

The ANT pin must be connected to the antenna connector by means of a transmission line with nominal
characteristics impedance as close as possible to 50

.