User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 93 of 147
2.4.2 Antenna detection interface (ANT_DET)
2.4.2.1 Guidelines for ANT_DET circuit design
Figure 45 and Table 34 describe the recommended schematic / components for the antennas detection circuit
that must be provided on the application board and for the diagnostic circuit that must be provided on the
antennas’ assembly to achieve primary and secondary antenna detection functionality.
Application Board
Antenna Cable
TOBY-R2 series
81
ANT1
75
ANT_DET
R1
C1 D1
C2
J1
Z
0
= 50 ohm Z
0
= 50 ohm
Z
0
= 50 ohm
Primary Antenna Assembly
R2
C4
L3
Radiating
Element
Diagnostic
Circuit
L2
L1
Antenna Cable
87
ANT2
C3
J2
Z
0
= 50 ohm Z
0
= 50 ohm
Z
0
= 50 ohm
Secondary Antenna Assembly
R3
C5
L4
Radiating
Element
Diagnostic
Circuit
Figure 45: Suggested schematic for antenna detection circuit on application board and diagnostic circuit on antennas assembly
Reference
Description
Part Number - Manufacturer
C1
27 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H270J - Murata
C2, C3
33 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H330J - Murata
D1
Very Low Capacitance ESD Protection
PESD0402-140 - Tyco Electronics
L1, L2
68 nH Multilayer Inductor 0402 (SRF ~1 GHz)
LQG15HS68NJ02 - Murata
R1
10 k Resistor 0402 1% 0.063 W
RK73H1ETTP1002F - KOA Speer
J1, J2
SMA Connector 50  Through Hole Jack
SMA6251A1-3GT50G-50 - Amphenol
C4, C5
22 pF Capacitor Ceramic C0G 0402 5% 25 V
GRM1555C1H220J - Murata
L3, L4
68 nH Multilayer Inductor 0402 (SRF ~1 GHz)
LQG15HS68NJ02 - Murata
R2, R3
15 k Resistor for Diagnostic
Various Manufacturers
Table 34: 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 45 and Table 34 are explained here:
 When antenna detection is forced by AT+UANTR command, ANT_DET generates a DC current measuring
the resistance (R2 // R3) from antenna connectors (J1, J2) provided on the application board to GND.
 DC blocking capacitors are needed at the ANT1 / ANT2 pins (C2, C3) and at the antenna radiating element
(C4, C5) 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, L2) and in series at the diagnostic resistor (L3, L4), to avoid a reduction of the RF
performance of the system, improving the RF isolation of the load resistor.
 Additional components (R1, C1 and D1 in Figure 45) are needed at the ANT_DET pin as ESD protection
 The ANT1 / ANT2 pins must be connected to the antenna connector by means of a transmission line with
nominal characteristics impedance as close as possible to 50 .