Rainbow Electronics ATR0630 - Manual (Page 4)

4
4920A–GPS–01/06
ATR0630 [Preliminary]
2.2 General Description
The ATR0630 has been designed especially for mobile applications. It provides high isolation
between GPS and cellular bands, as well as very low power consumption.
ATR0630 is based on the successful ANTARIS4 technology which includes the ANTARIS ROM
software, developed by u-blox AG, Switzerland. ANTARIS provides a proven navigation engine
which is used in high-end car navigation systems, automatic vehicle location (AVL), security and
surveying systems, traffic control, road pricing, and speed camera detectors, and provides loca-
tion-based services (LBS) worldwide.
The ANTARIS4 chipset has a very low power consumption and comes with a very low BoM for
the passive components. Especially, due to its fast search engine and GPS accelerator, the
ATR0630 only needs a GPS crystal (XTAL) as a resonator for the integrated crystal oscillator of
the ATR0630. This saves the considerable higher cost of a TCXO which is required for competi-
tor’s systems. Also, as the powerful standard software is available in ROM, no external flash
memory is needed.
The L input signal (f
RF
) is a Direct Sequence Spread Spectrum (DSSS) signal with a center fre-
quency of 1575.42 MHz. The digital modulation scheme is Bi-Phase-Shift-Keying (BPSK) with a
chip rate of 1.023 Mbps.
2.3 PMSS Logic
The power management, startup and shutdown (PMSS) logic ensures reliable operation within
the recommended operating conditions. The external power control signals PUrf and PUxto are
passed through Schmitt trigger inputs to eliminate voltage ripple and prevent undesired behavior
during start-up and shut-down. Digital and analog supply voltages are analyzed by a monitoring
circuit, enabling the startup of the IC only when it is within a safe operating range.
2.4 XTO
The XTO is designed for minimum phase noise and frequency perturbations. The balanced
topology gives maximum isolation from external and ground coupled noise. The built-in jump
start circuitry ensures reliable start-up behavior of any specified crystal. For use with an external
TCXO, the XTO circuitry can be used as a single-ended or balanced input buffer.
The recommended reference frequency is: f
XTO
= 23.104 MHz.
2.5 VCO/PLL
The frequency synthesizer features a balanced VCO and a fully integrated loop filter, thus no
external components are required. The VCO combines very good phase noise behavior and
excellent spurious suppression. The relation between the reference frequency (f
XTO
) and the
VCO center frequency (f
VCO
) is given by: f
VCO
= f
XTO
×
64 = 23.104 MHz
×
64 = 1478.656 MHz.
2.6 RF Mixer/Image Filter
Combined with the antenna, an external LNA provides a first band-path filtering of the signal.
Atmel’s ATR0610 is recommended for the LNA due to its low noise figure, high linearity and low
power consumption. The output of the LNA drives a SAW filter, which provides image rejection
for the mixer and the required isolation to all GSM bands. The output of the SAW filter is fed into
a highly linear mixer with high conversion gain and excellent noise performance.