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ATR0601-PFQW Datasheet(PDF) 3 Page - ATMEL Corporation |
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ATR0601-PFQW Datasheet(HTML) 3 Page - ATMEL Corporation |
3 / 18 page 3 4866G–GPS–11/06 ATR0601 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 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. 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: fVCO =fXTO × 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-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 IF) is given by: fIF = fRF – fVCO = 1575.42 MHz – 1478.656 MHz = 96.764 MHz. 3.6 IF-filter 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. |
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