MDEV-GPS-RM datasheet(6/27 Pages) LINX

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Time To First Fix (TTFF)

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 up to 30 seconds to acquire its position.

Warm: 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: A hot start is when the receiver has valid ephemeris, time, and

almanac data. In a hot start, the receiver takes 1 second 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

The RM Series GPS Receiver module is based on the MediaTek MT3337E

chipset, which consumes less power than competitive products while

providing exceptional performance even in dense foliage and urban

canyons. No external RF components are needed other than an antenna.

The simple serial interface and industry standard NMEA protocol make

integration of the RM Series into an end product extremely straightforward.

The module’s high-performance RF architecture allows it to receive GPS

signals that are as low as –161dBm. The RM Series can track up to 22

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.

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 it is powered back on. The memory and

clock pull about 6µA. 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 backup battery must be installed for the module to be enabled.

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.

Figure 7: Supply Filter

1PPS

GND

LCKIND

GND 20

RFIN 19

GND 18

VOUT 17

NC 16

GND 22

NC 15

NC 14

NC 13

VCC 12

VBACKUP 11

VCC

GND

RESET

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