Ublox TOBY-R2 Series System Integration Manual

Also see for TOBY-R2 Series: User guide

Contents

Ublox TOBY-R2 Series System Integration Manual Manual pdf 92 page image

TOBY-R2 series - System integration manualUBX-16010572 - R10 Design-in Page 92 of 1512.4.2 Antenna detection interface (ANT_DET)2.4.2.1 Guidelines for ANT_DET circuit designFigure 45 and Table 35 describe the recommended schematic / components for the antennasdetection circuit that must be provided on the application board and for the diagnostic circuit thatmust be provided on the antennas’ assembly to achieve primary and secondary antenna detectionfunctionality.Application BoardAntenna CableTOBY-R2 series81ANT175ANT_DET R1C1 D1C2 J1Z0 = 50 ohmZ0 = 50 ohmZ0 = 50 ohmPrimary Antenna AssemblyR2C4L3RadiatingElementDiagnosticCircuitL2L1Antenna Cable87ANT2 C3 J2Z0 = 50 ohmZ0 = 50 ohmZ0 = 50 ohmSecondary Antenna AssemblyR3C5L4RadiatingElementDiagnosticCircuitFigure 45: Suggested schematic for antenna detection circuit on application PCB and diagnostic circuit on antenna assemblyReference Description Part Number - ManufacturerC1 27 pF Capacitor Ceramic C0G 0402 5% 50 V GRM1555C1H270J - MurataC2, C3 33 pF Capacitor Ceramic C0G 0402 5% 50 V GRM1555C1H330J - MurataD1 Very Low Capacitance ESD Protection PESD0402-140 - Tyco ElectronicsL1, L2 68 nH Multilayer Inductor 0402 (SRF ~1 GHz) LQG15HS68NJ02 - MurataR1 10 k Resistor 0402 1% 0.063 W RK73H1ETTP1002F - KOA SpeerJ1, J2 SMA Connector 50  Through Hole Jack SMA6251A1-3GT50G-50 - AmphenolC4, C5 22 pF Capacitor Ceramic C0G 0402 5% 25 V GRM1555C1H220J - MurataL3, L4 68 nH Multilayer Inductor 0402 (SRF ~1 GHz) LQG15HS68NJ02 - MurataR2, R3 15 k Resistor for Diagnostic Various ManufacturersTable 35: Suggested parts for antenna detection circuit on application PCB and diagnostic circuit on antennas assemblyThe antenna detection circuit and diagnostic circuit suggested in Figure 45 and Table 35 areexplained here: When antenna detection is forced by AT+UANTR command, ANT_DET generates a DC currentmeasuring the resistance (R2 // R3) from antenna connectors (J1, J2) provided on the applicationboard to GND. DC blocking capacitors are needed at the ANT1 / ANT2 pins (C2, C3) and at the antenna radiatingelement (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 seriesat the ANT_DET pin (L1, L2) and in series at the diagnostic resistor (L3, L4), to avoid a reduction ofthe 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 ESDprotection The ANT1 / ANT2 pins must be connected to the antenna connector by means of a transmissionline with nominal characteristics impedance as close as possible to 50 .The DC impedance at RF port for some antennas may be a DC open (e.g. linear monopole) or a DC shortto reference GND (e.g. PIFA antenna). For those antennas, without the diagnostic circuit of Figure 45,the measured DC resistance is always at the limits of the measurement range (respectively open orshort), and there is no means to distinguish between a defect on antenna path with similarcharacteristics (respectively: removal of linear antenna or RF cable shorted to GND for PIFA antenna).