User Manual
Table Of Contents
- Document History
- Introduction
- Product Concept
- GSM Application Interface
- GSM/GPRS Operating Modes
- Power Supply
- Power Up / Down Scenarios
- Automatic GPRS Multislot Class Change
- Charging Control of the GSM Part
- Power Saving
- Summary of State Transitions (Except SLEEP Mode)
- RTC Backup for GSM Part of XT55/56
- Serial Interfaces of the XT55/56 GSM Part
- Audio Interfaces
- SIM Interface
- Control Signals
- GPS Application Interface
- GSM and GPS Antenna Interfaces
- Electrical, Reliability and Radio Characteristics
- Mechanics
- Reference Approval
- Example Applications
- List of Parts and Accessories
XT55/56 Hardware Interface Description
Confidential / Preliminary
s
XT55/56_hd_v02.96 Page 81 of 125 18.08.2005
5 GSM and GPS Antenna Interfaces
5.1 GSM Antenna Installation
The RF interface has an impedance of 50. XT55/56 is capable of sustaining a total
mismatch at the antenna connector or pad without any damage, even when transmitting at
maximum RF power.
The external antenna must be matched properly to achieve best performance regarding
radiated power, DC-power consumption and harmonic suppression. Matching networks are
not included on the XT55/56 PCB and should be placed in the host application.
Regarding the return loss XT55/56 provides the following values:
Table 20: Return loss
State of module Return loss of module Recommended return loss of application
Receive > 8dB > 12dB
Transmit not applicable > 12dB
Idle < 5dB not applicable
The connection of the antenna or other equipment must be decoupled from DC voltage.
5.1.1 GSM antenna Connector
To suit the physical design of individual applications XT55/56 offers two alternative
approaches to connecting the GSM antenna:
• Recommended approach: U.FL-R-SMT antenna connector from Hirose assembled on
the component side of the PCB (top view on XT55/56). See Chapter 5.3 for details.
• Antenna pad and grounding plane placed on the bottom side. See Chapter 5.1.2.
Figure 31: U.FL-R-SMT connector Figure 32: Antenna pad and GND plane
Antenna pad
Antenna ground