RXM-GPS-SR-T Linx Technologies Inc, RXM-GPS-SR-T Datasheet - Page 3

• Manufacturer Part Number: RXM-GPS-SR-T
• Description: GPS MODULE SMD SIRF W/ANT
• Manufacturer: Linx Technologies Inc
• Series: SRr
• Type: GPS Receiver Moduler

Specifications of RXM-GPS-SR-T

• Package / Case: Module
• Operating Voltage: 3 V to 4.3 V
• Operating Current: 31 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

A BRIEF OVERVIEW OF GPS
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The Global Positioning System (GPS) is a U.S.-owned utility that freely and
continuously provides positioning, navigation, and timing (PNT) information.
Originally created by the U.S. Department of Defense for military applications,
the system was made available without charge to civilians in the early 1980s.
The global positioning system consists of a nominal constellation of 24 satellites
orbiting the earth at about 12,000 nautical miles in height. The pattern and
spacing of the satellites allow at least four to be visible above the horizon from
any point on the Earth. Each satellite transmits low power radio signals which
contain three different bits of information; a pseudorandom code identifying the
satellite, ephemeris data which contains the current date and time as well as the
satellite’s health, and the almanac data which tells where each satellite should
be at any time throughout the day.
A GPS receiver such as the Linx SR Series GPS module receives and times the
signals sent by multiple satellites and calculates the distance to each satellite. If
the position of each satellite is known, the receiver can use triangulation to
determine its position anywhere on the earth. The receiver uses four satellites to
solve for four unknowns; latitude, longitude, altitude, and time. If any of these
factors is already known to the system, an accurate position (Fix) can be
obtained with fewer satellites in view. Tracking more satellites improves
calculation accuracy. In essence, the GPS system provides a unique address for
every square meter on the planet.
A faster Time To First Fix (TTFF) is also possible if the satellite information is
already stored in the receiver. If the receiver knows some of this information,
then it can accurately predict its position before acquiring an updated position fix.
For example, aircraft or marine navigation equipment may have other means of
determining altitude, so the GPS receiver would only have to lock on to three
satellites and calculate three equations to provide the first position fix after
power-up.
TTFF is often broken down into three parts:
Cold: A cold start is when the receiver has no accurate knowledge of its position
or time. This happens when the receiver’s internal Real Time Clock (RTC) has
not been running or it has no valid ephemeris or almanac data. In a cold start,
the receiver takes 35 to 40 seconds to acquire its position. If new almanac data
is required, this may take up to 15 minutes (see page 7 for more details).
Warm or Normal: A typical warm start is when the receiver has valid almanac
and time data and has not significantly moved since its last valid position
calculation. This happens when the receiver has been shut down for more than
2 hours, but still has its last position, time, and almanac saved in memory, and
its RTC has been running. The receiver can predict the location of the current
visible satellites and its location; however, it needs to wait for an ephemeris
broadcast (every 30 seconds) before it can accurately calculate its position.
Hot or Standby: A hot start is when the receiver has valid ephemeris, time, and
almanac data. This happens when the receiver has been shut down for less than
2 hours and has the necessary data stored in memory with the RTC running. In
a hot start, the receiver takes 1 to 2 seconds to acquire its position. The time to
calculate a fix in this state is sometimes referred to as Time to Subsequent Fix
or TTSF.
MODULE DESCRIPTION
BACKUP BATTERY
POWER SUPPLY REQUIREMENTS
THE LED OUTPUT
The SR Series is a high performance self-contained GPS receiver in a compact
RoHS compliant surface mount package. 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 features an integral antenna, LNA and SAW filter,
so no external RF components are needed. The simple serial interface and
industry standard NMEA protocol make integration of the SR 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 SR
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 SR Series 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 module 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.
When a position fix is available, this line outputs a single 50mS pulse every
second. If no fix is available, then it is low. This is suitable for connection to an
LED or other indicator to tell the user that a valid fix has been acquired. When
the module is in sleep mode, this line is an input with an internal 100kΩ pull-down
resistor.
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