3. TECHNICAL BRIEF
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Of course, passband ripple and return loss are still important in all cases for the same reasons
explained in the antenna switch module and duplexer sections.
3.5.9 VCTCXO (X100)
The Voltage Controlled Temperature Compensated Crystal Oscillator (VCTCXO) provides the
reference frequency for all RFIC synthesizers as well as clock generation functions within the
MSM6275 IC. The 6275-series chipset requires a 19.2 MHz nominal VCTCXO frequency. The
oscillator frequency is controlled by the MSM6275’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.
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