Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 65 of 119
2.4.2 Antenna detection interface (ANT_DET)
2.4.2.1 Guidelines for ANT_DET circuit design
Figure 35 and Table 25 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 antenna detection functionality.
Applicat ion Board
Ant enna Cable
SARA-R4/ N4
56
ANT
62
ANT_DET
R1
C1 D1
L1
C2
J 1
Z
0
= 50 Ω Z
0
= 50 Ω
Z
0
= 50 ohm
Ant enna Assembly
R2
C4
L3
Radiat ing
Elem ent
Diagnost ic
Circuit
GND
L2
C3
Figure 35: Suggested schematic for antenna detection circuit on application PCB 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 kΩ Resistor 0402 1% 0.063 W
RK73H1ETTP1002F - KOA Speer
J1
SMA Connector 50 Ω 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 kΩ Resistor for Diagnostics
Various Manufacturers
Table 25: Suggested parts for antenna detection circuit on application PCB and diagnostic circuit on antennas assembly
The antenna detection circuit and diagnostic circuit suggested in Figure 35 and Table 25 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 35) are needed at the ANT_DET pin as ESD protection.
• Additional high pass filter (C3 and L2 in Figure 35) 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 Ω.
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 of Figure 35, the measured DC resistance is always
at the limits of the measurement range (respectively open or short), and there is no mean to distinguish between a defect