ATR0601 Datasheet, PDF (3/17 Pages) ATMEL Corporation – GPS FRONT-END IC

ATR0601 [Preliminary]
3. Functional Description
3.1 General Description
The ATR0601 GPS receiver IC has been especially designed for GPS applications in both
mobile phone and automotive applications. From this system point of view, it incorporates high-
est isolation between GPS and cellular bands, as well as very low power consumption.
The L1 input signal (f_RF) is a Direct Sequence Spread Spectrum (DSSS) signal with a centre fre-
quency of: f_RF = 1575.42 MHz. The digital modulation scheme is Bi-Phase-Shift-Keying (BPSK)
with a chip rate of 1.023 Mbps. As the input signal power at the antenna is approximately
–140 dBm, the desired signal is below the thermal noise floor.
3.2 PMSS Logic
The Power Management, Startup and Shutdown Logic ensures reliable operation within the rec-
ommended operating conditions. The external power control signals PUrf and PUxto are passed
thru Schmitt-trigger inputs to eliminate voltage ripple and prevent undesired behaviour during
startup and shutdown. Digital and analog supply voltages are analyzed by a monitoring circuit,
enabling the startup of the IC only within a secure operating area.
3.3 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 behaviour of any specified crystal. For use with an exter-
nal 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.
3.4 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 behaviour and
excellent spurious suppression. The relation between the reference frequency (f_XTO) and the
VCO centre frequency (f_VCO) is given by: f_VCO = f_XTO × 64 = 23.104 MHz × 64 = 1478.656 MHz.
3.5 RF-Mixer/Image-filter
Combined with the antenna an external LNA provides a first band path filtering of the signal. For
the LNA, Atmel’s ATR0610 is recommended, due to it’s low Noise Figure, high linearity an low
power consumption. The output of the LNA drives an SAW filter, which provides image rejection
for the mixer and the required isolation of all GSM bands. The output of the SAW filter is fed into
a highly linear mixer with high conversion gain and excellent noise performance.
The IF frequency (f_IF) is given by: f_IF = f_RF – f_VCO = 1575.42 MHz – 1478.656 MHz = 96.764 MHz.
3.6 IF-filter
The mixer directly drives an external LC-Bandpath filter via open collector outputs. In order to
provide highest selectivity and conversion gain, it is recommended to design the external filter,
according to the application proposal, as a 2-pole filter with a quality factor Q > 25.
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4866A–GPS–08/05