RXM-GPS-SG-T Linx Technologies Inc, RXM-GPS-SG-T Datasheet - Page 4

• Manufacturer Part Number: RXM-GPS-SG-T
• Description: GPS MODULE SMD SIRF
• Manufacturer: Linx Technologies Inc
• Series: SGr
• Type: GPS Moduler

Specifications of RXM-GPS-SG-T

• Package / Case: Module
• Operating Voltage: 4.2 V
• Operating Current: 46 mA
• Frequency Range: 1575.42 MHz
• Interface Type: UART, USB
• Operating Temperature Range: - 30 C to + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Voltage - Supply: -
• Frequency: -
• Operating Temperature: -
• Applications: -
• Sensitivity: -
• Memory Size: -
• Data Interface: -
• Data Rate - Maximum: -
• Modulation Or Protocol: -
• Antenna Connector: -
• Current - Receiving: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

MODULE DESCRIPTION
ANTENNA CONSIDERATIONS
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By default, the SG Series will operate in full power mode. However, it also has a
built-in power control mode called Adaptive Trickle Power mode. The module is
based on the SiRFstar III low power chipset, which consumes significantly less
power than competitive products while providing exceptional performance even
in dense foliage and urban canyons. The module includes an internal SAW filter
and LNA, so no external RF components are needed other than an antenna. The
simple serial interface and industry standard NMEA protocol make integration of
the SG Series receiver into an end product or system extremely straightforward.
The module’s high-performance RF architecture allows it to receive GPS signals
that are as low as -159dBm. With over 200,000 effective correlators, the SG
Series can track up to 20 satellites at the same time. Once locked onto the visible
satellites, the receiver calculates the range to the satellites and determines its
position and the precise time. It then outputs the data through a standard serial
port using several standard NMEA protocol formats.
The GPS core handles all of the necessary initialization, tracking, and
calculations autonomously, so no programming is required. The RF section is
optimized for low level signals, and requires no production tuning of any type.
The SG Series module is designed to utilize a wide variety of external antennas.
The module has a regulated power output which simplifies the use of GPS
antenna styles which require external power. This allows the designer great
flexibility, but care must be taken in antenna selection to ensure optimum
performance. For example, a handheld device may be used in many varying
orientations so an antenna element with a wide and uniform pattern may yield
better overall performance than an antenna element with high gain and a
correspondingly narrower beam. Conversely, an antenna mounted in a fixed and
predictable manner may benefit from pattern and gain characteristics suited to
that application. Evaluating multiple antenna solutions in real-world situations is
a good way to rapidly assess which will best meet the needs of your application.
For GPS, the antenna should have good right hand circular polarization
characteristics (RHCP) to match the polarization of the GPS signals. Ceramic
patches are the most commonly used style of antenna, but there are many
different shapes, sizes and styles of antennas available. Regardless of the
construction, they will generally be either passive or active types. Passive
antennas are simply an antenna tuned to the correct frequency. Active antennas
add a Low Noise Amplifier (LNA) after the antenna and before the module to
amplify the weak GPS satellite signals.
For active antennas, the VOUT line can provide 2.85V at 30mA to power the
external LNA. A 300 ohm ferrite bead should be used to connect this line to the
RFIN line. This bead will prevent the RF from getting into the power supply, but
will allow the DC voltage onto the RF trace to feed into the antenna. A series
capacitor inside the module prevents this DC voltage from affecting the bias on
the module’s internal LNA.
Maintaining a 50 ohm path between the module and antenna is critical. Errors in
layout can significantly impact the module’s performance. Please review the
layout guidelines elsewhere in this guide carefully to become more familiar with
these considerations.
BACKUP BATTERY
POWER SUPPLY REQUIREMENTS
THE 1PPS OUTPUT
GENERAL PURPOSE I/O
THE LOCK INDICATOR LINE
Figure 3: SG Series Lock Indicator Signals
The module is designed to work with a backup battery that keeps the SRAM
memory and the RTC powered when the RF section and the main GPS core are
powered down. This enables the module to have a faster Time To First Fix
(TTFF) when the it is powered back on. The memory and clock pull about 10µA.
This means that a small lithium battery is sufficient to power these sections. This
significantly reduces the power consumption and extends the main battery life
while allowing for fast position fixes when the module is powered back on.
The module requires a clean, well-regulated power source. While it is preferable
to power the unit from a battery, it can operate from a power supply as long as
noise is less than 20mV. Power supply noise can significantly affect the
receiver’s sensitivity, therefore providing clean power to the module should be a
high priority during design. Bypass capacitors should be placed as close as
possible to the module. The values should be adjusted depending on the amount
and type of noise present on the supply line.
The 1PPS line outputs 1 pulse per second on the rising edge of the GPS second
when the receiver has an over-solved navigation solution from five or more
satellites. The pulse has a duration of 1µS and an accuracy of about 1µS from
the GPS second. This line is low until the receiver acquires an over-solved
navigation solution (a lock on more than 4 satellites). The GPS second is based
on the atomic clocks in the GPS satellites, which are monitored and set to
Universal Time master clocks. This output and the time calculated from the GPS
satellite transmissions can be used as a clock feature in an end product.
The SG Series module has five general purpose I/Os (GPIOs) that are
configured using four simple input messages: set the I/Os as inputs or outputs,
read the states of the inputs, write the states of the outputs, and read the current
configuration and states of all of the GPIOs. This offers the system additional
lines without increasing the size or load on the user’s microcontroller. Refer to
the NMEA Input Messages section for details on the commands.
The Lock Indicator line outputs a series of 100mS pulses with a 50% duty cycle
when the module is searching for a fix. Once the receiver acquires a solution, the
line outputs a single 100mS pulse every second. This line can be connected to
a microcontroller to monitor the state of the module or connected to an LED as
a visual indicator.
Voltage
0
Position Fixed
1
Seconds
Voltage
0
Searching for Fix
1
Seconds
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