Motorola D10 Service Manual page 111

BenQ Rev 1.0
not reject the noise from the modulator sufficiently. The ideal bandwidth
will be a compromise between these factors depending on the noise
performance of the VCO and amplifier chain. The OPLL phase detector
current changes automatically between GSM900, DCS1800 and
PCS1900 to match the tuning characteristics of the transmit VCO. This
allows a OPLL signal loop filter to be used on all bands.
4. Synthesizer:
The RFVCO/RF synthesiser generates the RFLO signal. The RFVCO
band is selected automatically depending on the final output frequency.
The RF synthesizer sets the RFVCO frequency and includes fast- lock
features to improve the synthesizer settling time. In addition, the RF
synthesizer scales the phase detector current to maintain constant loop
characteristics across the full 3.5~4GHz operating range. The IFVCO is
controlled by the IF synthesizer and is used for transmit bursts only.
VCXO
The B5E RFIC is capable of operating with external crystal (U801)
instead of TCXO module, which includes a single transistor and
capable of being configured as a voltage controlled crystal oscillator
with minimum external component. In addition, the IC includes a
divide-by-2. Through proper selection of crystal accompanied by careful
external circuit design effort, sufficient frequency control range could be
achieved.
RFVCO/IFVCO
The IC integrates two RF frequency synthesizers, which control the
RFLO and the IFLO oscillators.
5. Regulator
U751 and U752 are two single LDO. The first single LDO (U751)
provides PLL synthesizer and RFVCO of transceiver (U601). The
second one (U752) provides V_BR of PA (U708) and the Vcc pins of
transceiver except the Vcc of PLL synthesizer, RFVCO. Both these dual
regulators can be shut down simultaneously by TCXOEN signal (U1 pin
E11).
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