ATR0601_06 ATMEL [ATMEL Corporation], ATR0601_06 Datasheet - Page 3

• Manufacturer Part Number: ATR0601_06
• Description: GPS Front-end IC
• Manufacturer: ATMEL [ATMEL Corporation]

3. Functional Description
3.1
3.2
3.3
3.4
3.5
3.6
4866G–GPS–11/06
General Description
PMSS Logic
XTO
VCO/PLL
RF-Mixer/Image-filter
IF-filter
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
quency of: f
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.
The Power Management, Startup and Shutdown Logic ensures reliable operation within the rec-
ommended operating and timing conditions. The external power control signals PUrf and PUxto
are passed thru Schmitt-trigger inputs, digital and analog supply voltages are analyzed by moni-
toring circuits.
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
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
VCO centre frequency (f
Combined with the antenna an external LNA provides a first band-pass 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
The mixer directly drives an external LC band-pass 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.
RF
= 1575.42 MHz. The digital modulation scheme is Bi-Phase-Shift-Keying (BPSK)
IF
) is given by: f
RF
) is a Direct Sequence Spread Spectrum (DSSS) signal with a centre fre-
VCO
) is given by: f
IF
= f
RF
– f
VCO
XTO
VCO
= f
= 23.104 MHz.
= 1575.42 MHz – 1478.656 MHz = 96.764 MHz.
XTO
64 = 23.104 MHz
64 = 1478.656 MHz.
ATR0601
XTO
) and the
3