RXM-GPS-SG
WIRELESS MADE SIMPLE
®
SG SERIES GPS RECEIVER MODULE DATA GUIDE
DESCRIPTION
0.591
The SG Series GPS receiver module is a self-
(15.00)
contained high-performance GPS receiver with an
on-board LNA and SAW filter. Based on the SiRFstar
III chipset, it provides exceptional sensitivity, even in
dense foliage and urban canyons. The module’s very
0.512
GPS MODULE
(13.00)
low power consumption helps maximize runtimes in
RXM-GPS-SG
battery powered applications. With over 200,000
effective correlators, the SG Series receiver can
LOT GRxxxx
acquire and track up to 20 satellites simultaneously in
0.087
just seconds, even at the lowest signal levels.
(2.20)
Housed in a compact reflow-compatible SMD
package, the receiver requires no programming or
Figure 1: Package Dimensions
additional RF components (except an antenna) to form a complete GPS solution.
Five GPIOs are easily configured through simple serial commands. These features,
along with the module’s standard NMEA data output, make the SG Series easy to
integrate, even by engineers without previous RF or GPS experience.
FEATURES
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
SiRF Star III chipset
200,000+ correlators
Low power consumption (46mW)
High sensitivity (-159dBm)
20 channels
Fast TTFF at low signal levels
Battery-backed SRAM
5 User Definable GPIOs
No programming necessary
n
No external RF components needed
(except an antenna)
n
No production tuning
n
Direct serial interface
n
Power down feature
n
Compact surface-mount package
n
Manual or reflow compatible
n
RoHS compliant
APPLICATIONS INCLUDE
Positioning and Navigation
Location and Tracking
Security/Loss-Prevention
Surveying
Logistics
Fleet Management
ORDERING INFORMATION
PART #
DESCRIPTION
RXM-GPS-SG-x
GPS Receiver Module
MDEV-GPS-SG
Master Development System
x = “T” for Tape and Reel, “B” for Bulk
Reels are 1,000 pcs.
Quantities less than 1,000 pcs. are supplied in bulk
Revised 1/10/11
ELECTRICAL SPECIFICATIONS
Parameter
POWER SUPPLY
Supply Voltage
Supply Current:
Peak
Acquisition
Tracking
Standby
Backup Battery Voltage
Backup Battery Current
2.85V Output Voltage
2.85V Output Current
Output Logic Low Voltage
Output Logic High Voltage
Output Logic Low Current
Output Logic High Current
Input Logic Low Voltage
Input Logic High Voltage
Input Logic Low Current
With Pull-down
Input Logic High Current
With Pull-down
Input Capacitance
Output Capacitance
LNA SECTION
Insertion Power Gain
Noise Figure
ANTENNA PORT
RF Input Impedance
ENVIRONMENTAL
Operating Temperature Range
Storage Temperature Range
RECEIVER SECTION
Receiver Sensitivity
Tracking
Cold Start
Acquisition Time
Hot Start (Open Sky)
Hot Start (Indoor)
Cold Start
Position Accuracy
Autonomous
SBAS
Altitude
Velocity
Chipset
Firmware Version
Frequency
Channels
Update Rate
Protocol Support
Designation
V
CC
I
CC
–
–
–
–
1.3
–
2.79
–
–
0.75*V
OUT
–
–
-0.3
0.7*V
OUT
-60
–
-60
–
–
–
–
–
–
-30
-40
–
32
28
1.5
–
10
2.85
–
–
–
2
2
–
–
–
–
–
–
–
–
18
0.9
50
–
25
46.0
–
–
–
6.0
–
2.91
30
0.25*V
OUT
–
–
–
0.3*V
OUT
3.6
20
60
20
60
4
4
–
–
–
+85
+85
mA
mA
mA
mA
VDC
µA
VDC
mA
VDC
VDC
mA
mA
VDC
VDC
µA
µA
µA
µA
pF
pF
dB
dB
Ω
Min.
3.0
Typical
–
Max.
4.2
Units
VDC
Notes
1
2
6
6
6
6
–
–
–
3
–
–
–
–
–
–
–
–
–
–
–
4
5
5
–
–
–
Notes:
1.
2.
3.
4.
5.
6.
I
OUT
= 0
V
CC
=
3.3V,
I
OUT
= 0
V
CC
=
3.3V
Output buffer
At 25
°
C
With passive antenna. Active antennas will increase current consumption.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage V
CC
Input Battery Backup Voltage
2.85V Output Current
Operating Temperature
Storage Temperature
Soldering Temperature
+6.5
+7.0
50
-30
to
+85
-40
to
+125
+225°C for 10 seconds
VDC
VDC
mA
°C
°C
V
BAT
I
BAT
V
OUT
I
OUT
V
OL
V
OH
I
OL
I
OH
V
IL
V
IH
I
IL
I
IH
C
IN
C
OUT
|S
21
|
2
NF
R
IN
–
–
*NOTE*
Exceeding any of the limits of this section may lead to permanent
damage to the device. Furthermore, extended operation at these maximum
ratings may reduce the life of this device.
*CAUTION*
This product incorporates numerous static-sensitive components.
Always wear an ESD wrist strap and observe proper ESD handling
procedures when working with this device. Failure to observe this
precaution may result in module damage or failure.
ONLINE RESOURCES
®
°
C
°
C
–
–
–
–
–
-159
-144
–
–
35
–
–
2
15
–
10
5
60,000
1,000
dBm
dBm
S
S
S
m
m
ft
Knots
–
–
–
–
–
–
–
–
–
www.linxtechnologies.com
–
–
–
–
–
–
–
–
SiRF Star III, GSC3f/LPx 7990
GSW3.5.0_3.5.00.00-SDK-3EP2.01A
•
•
•
•
•
Latest News
Data Guides
Application Notes
Knowledgebase
Software Updates
L1 1575.42MHz, C/A Code
20
1Hz
NMEA 0183 ver
3.0,
SiRF Binary
If you have questions regarding this or any Linx product make
www.linxtechnologies.com your first stop. Day or night, the Linx website gives
you instant access to the latest information regarding the products and services
of Linx. It’s all here: manual and software updates, application notes, a
comprehensive knowledgebase, FCC information, and much more. Here you will
find the answers you need arranges in an intuitive format. Be sure to visit often!
Page
3
Table 1: SG Series Receiver Specifications
Page 2
PIN ASSIGNMENTS
1
2
3
4
5
21
6
7
8
9
10
NC
NC
1PPS
TXA
RXA
GND
GPIO10
LCKIND
GPIO1
RFPWRUP
ON_OFF
GND
RFIN
GND
VOUT
NC
GND
GPIO13
GPIO15
GPIO14
VCC
VBACKUP
20
19
18
17
16
22
15
14
13
12
11
A BRIEF OVERVIEW OF GPS
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 SG 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 9 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.
Page 5
Figure 2: SG Series Receiver Pinout (Top View)
PIN DESCRIPTIONS
Pin #
1, 2, 16
3
4
5
6
7
8
9
10
Name I/O
NC
1PPS
TXA
RXA
GPIO10
LCKIND
GPIO1
RFPWRUP
ON_OFF
–
Description
No Connect. No electrical connection.
Pulse per second (1uS pulse)
Serial output for channel A (default NMEA)
Serial input for channel A (default NMEA)
General Purpose I/O
Lock Indicator
General Purpose I/O, 100kΩ pull down
Indicate power state
Edge triggered soft on/off request. Should only be
used to wake up the module when the RFPWRUP line
is low.
Backup battery supply voltage. This line must be
powered to enable the module.
Supply Voltage
General Purpose I/O, 100kΩ pull up
General Purpose I/O, 100kΩ pull up
General Purpose I/O
2.85V Linear regulator power output
Ground
GPS RF signal input
O
O
I
I/O
O
I/O
O
I
11
12
13
14
15
17
18,20-22
19
VBACKUP
VCC
GPIO14
GPIO15
GPIO13
VOUT
GND
RFIN
P
P
I/O
I/O
I/O
P
P
I
Page 4
MODULE DESCRIPTION
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.
BACKUP BATTERY
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.
POWER SUPPLY REQUIREMENTS
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 OUTPUT
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.
ANTENNA CONSIDERATIONS
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.
Page 6
GENERAL PURPOSE I/O
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
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
Voltage
0
Position Fixed
1
Seconds
0
1
Searching
for Fix
Seconds
Figure
3:
SG Series Lock Indicator Signals
Page 7
POWER CONTROL
The SG Series has a built-in power control mode called Adaptive Trickle Power
mode. In this mode, the receiver will power on at full power to acquire and track
satellites and obtain satellite data. It then powers off the RF stage and only uses
its processor stage (CPU) to determine a position fix (which takes about 160mS).
Once the fix is obtained, the receiver goes into a low power standby state. After
a user-defined period of time, the receiver wakes up to track the satellites for a
user-defined period of time, updates its position using the CPU only, and then
resumes standby. The initial acquisition time is variable, depending on whether
it is a cold start or assisted, but a maximum acquisition time is definable. This
cycling of power is ideal for battery-powered applications since it significantly
reduces the amount of power consumed by the receiver while still providing
similar performance to the full power mode.
In normal conditions, this mode provides a fixed power savings, but under poor
signal conditions, the receiver returns to full power to improve performance. The
receiver sorts the satellites according to signal strength and if the fourth satellite
is below 26dB-Hz, then the receiver switches to full power. Once the fourth
satellite is above
30dB-Hz,
the receiver returns to Adaptive Trickle Power mode.
For optimum performance, SiRF recommends cycle times of
300mS
track to 1S
interval or 400mS track to 2S interval. CPU time is about 160mS to compute the
navigation solution and empty the UART. There are some situations in which the
receiver stays in full power mode. These are: to collect periodic ephemeris data,
to collect periodic ionospheric data, to perform RTC convergence, and to
improve the navigation result. Depending on states of the power management,
the receiver will be in one of three system states:
Full Power State
All RF and baseband circuitry are fully powered. There is a difference in power
consumption during acquisition mode and tracking mode. Acquisition requires
more processing, so it consumes more power. This is the initial state of the
receiver and it stays in this state until a reliable position solution is achieved.
CPU Only State
This state is entered when the satellite measurements have been collected but
the navigation solution still needs to be computed. The RF and DSP processing
are no longer needed and can be turned off.
Stand-By State
In this state, the RF section is completely powered off and the clock to the
baseband is stopped. About 1mA of current is drawn in this state for the internal
core regulator, RTC and battery-backed RAM. The receiver enters this state
when a position fix has been computed and reported.
The table below shows the RFPWRUP and Vout conditions in each power state.
Power State
Full power
CPU only
Stand by
RFPWRUP
H
H
L
VOUT
Enabled
Enabled
Enabled
TYPICAL APPLICATIONS
Figure 4 shows a circuit using the GPS module with a passive antenna.
VCC
VCC
µP
RX
TX
GND
GND
GND
1
2
3
4
5
21
6
7
8
9
10
NC
NC
1PPS
TXA
RXA
GND
GPIO10
LCKIND
GPIO1
RFPWRUP
ON_OFF
GND
RFIN
GND
VOUT
NC
GND
GPIO13
GPIO15
GPIO14
VCC
VBACKUP
20
19
18
17
16
22
15
14
13
12
11
GND
VCC
GND
Figure 4: SG Series Module with a Passive Antenna
Figure 5 shows a circuit using the GPS module with an active antenna.
VCC
VCC
µP
RX
TX
GND
GND
GND
1
2
3
4
5
21
6
7
8
9
10
NC
NC
1PPS
TXA
RXA
GND
GPIO10
LCKIND
GPIO1
RFPWRUP
ON_OFF
GND
RFIN
GND
VOUT
NC
GND
GPIO13
GPIO15
GPIO14
VCC
VBACKUP
20
19
18
17
16
22
15
14
13
12
11
300Ω
Ferrite Bead
GND
VCC
GND
Figure 5: SG Series Module with an Active Antenna
SLOW START TIME
The most critical factors in start time are current ephemeris data, signal strength,
and sky view. The ephemeris data describes the path of each satellite as they
orbit the earth. This is used to calculate the position of a satellite at a particular
time. This data is only usable for a short period of time, so if it has been more
than a few hours since the last fix or if the location has significantly changed (a
few hundred miles), then the receiver may need to wait for a new ephemeris
transmission before a position can be calculated. The GPS satellites transmit
the ephemeris data every
30
seconds. Transmissions with a low signal strength
may not be received correctly or be corrupted by ambient noise. The view of the
sky is important because the more satellites the receiver can see, the faster the
fix and the more accurate the position will be when the fix is obtained.
If the receiver is in a very poor location, such as inside a building, urban canyon,
or dense foliage, then the time to first fix can be slowed. In very poor locations
with poor signal strength and a limited view of the sky with outdated ephemeris
data, this could be on the order of several minutes. In the worst cases, the
receiver may need to receive almanac data, which describes the health and
course data for every satellite in the constellation. This data is transmitted every
15 minutes. If a lock is taking a long time, try to find a location with a better view
of the sky and fewer obstructions. Once locked, it is easier for the receiver to
maintain the position fix.
Page 9
Table 2: RFPWRUP and VOUT conditions
Page
8
