LG -P970 Service Manual page 36

3. TECHNICAL BRIEF
The amplified GPS signal due to GPS LNA module, go into RFIP pin of U801 GPS chipset. Figure. shows the
schematic of GPS main circuit of P970. The internal LNA/mixer in U801 down-converts the 1575.42MHz GPS
signal to an intermediate frequency of approximately 6.2 MHz. Setting the IF at around 6MHz reduces the
sensitivity of the GPS RF to flicker noise and DC offset.
The TCXO (X801) makes 26MHz reference clock that drives the frequency synthesizer into U801 that generates
ut 1.5GHz LO signal. The frequency synthesizer conations a fraction-N PLL consisting of on-chip
abo
VCO
and supports a wide rage of reference frequencies, including all frequencies commonly specified in mobile
phone standards.
The GPS receiver input employs a single-ended connection realized by this pin. The GPS input is routed from the
GPS antenna switch, through a band pass filter and then an impedance transformer circuit that optimally
matches the impedance looking into the GPS LNA. The impedance transformer circuit topology is shown in
Figure 3.10.
[Figure 3.10] GPS Input Network Topology
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