LG L602i, Service Manual

Page: 32 / 192

3. TECHNICAL BRIEF
- 33 -
3.5.9 VCTCXO (X1000)
The Voltage Controlled Temperature Compensated Crystal Oscillator (VCTCXO) provides the
reference frequency for all RFIC synthesizers as well as clock generation functions within the
MSM6250A IC. The 6250-series chipset requires a 19.2 MHz nominal VCTCXO frequency . The
oscillator frequency is controlled by the MSM6250A’s TRK_LO_ADJ pulse density modulated signal in
the same manner as the transmit gain control.
The filtered PDM signal results in an analog control signal into the VCTCXO tuning port whose voltage
is directly proportional to the density of the digital bit stream. The MSM device varies the pulse density
to change the analog control voltage that sets the oscillator frequency - all within a feedback control
loop that minimizes handset frequency drift relative to the network.
Of course, passband ripple and return loss are still important in all cases for the same reasons
3.5.10 UMTS Rx VCO (X1001)
The UMTS Rx CH VCO is a key component within its phase-looked loop; VCO performance directly
impacts PLL and receiver performance.
The UMTS Rx CH LO signal originates in the external UMTS_RX_VCO, is buffered by RFR6202 IC
circuits, and routed to the RTR6250 IC PLL circuit. This VCO signal requires good microstrip and/or
stripline techniques since it transverses a significant length.
Z3X-BOX.COM