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8

9

Antenna Considerations

The R4 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, a 300 ohm ferrite bead can be used to connect the

VOUT line to the RFIN line. This bead prevents the RF from getting into the

power supply, but allows 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. The VOUT line is

connected to the VCC line, so the voltage is the module supply voltage and

the current sourcing depends on the module’s power supply.

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.

Power Control

The R4 Series GPS Receiver module offers two power control modes: Full

Power and Hibernate. In Full Power mode the module is fully active and

and continuously tracking. Measurements are of the highest quality and are

continuously output by the module. This is the highest current consumption

state.

Hibernate mode is the lowest power setting. The tracking and processor

blocks are powered down, but the RTC is still running and the memory

blocks are still powered enabling a hot start.

The module switches between these states by toggling the ON_OFF line.

The ON_OFF line must go high for at least 100ms to trigger the change of

state and must remain low for at least 100ms to reset the edge detector.

If the module is in Full Power mode, a pulse on the ON_OFF line will initiate

an orderly shutdown into Hibernate mode. If the module is in Hibernate

mode, a pulse on the ON_OFF line will transistion the module into Full

Power Mode.

ON_OFF

Full PowerHibernate

Full Power

Module

Power

100ms

100ms

Figure 7: R4 Series GPS Receiver Power Control