LG -P970 Service Manual page 38

3. TECHNICAL BRIEF
In the PMB 5703 the receiver and the transmitter contain each a complete fractional-N sigma-delta synthesizer
with fast locking. For GMSK/8-PSK RX operation mode a fractional-N sigma-delta synthesizer for the frequency
synthesis is used. For GMSK/8-PSK TX operation mode the fractional-N sigma-delta synthesizer is used as a
Sigma-Delta modulation loop to process the phase/frequency signal.
A 26 MHz reference signal (provided by an internal clock generation block) serves as comparison frequency of
the phase detector. In GMSK/8-PSK mode the divider in the feedback path of the synthesizer is carried out as a
multi-modulus divider (MMD). The GMSK/8-PSK loop filter is fully integrated and the loop bandwidth is about
100 kHz to allow the transfer of the phase modulation during GMSK/8-PSK operation. The open loop gain is
automatically adjusted prior to each GMSK/8-PSK slot . To overcome the statistical spread of the loopfilter
element values an automatic loopfilter adjustment is performed before each GMSK/8-PSK synthesizer startup.
The fully integrated GMSK/8-PSK quad-band VCO is designed for the four GMSK/8-PSK bands (850, 900,
1800,1900 MHz) and operates at double (for GSM1800 and GSM1900 band) or four times (for GSM850 and
GSM900 band) of the transmit or receive frequency. To cover the wide frequency range the VCO is automatically
aligned by a binary automatic band selection before the settling process of the synthesizer starts. In UMTS TX
and RX mode a fractional-N sigma-delta synthesizer for the frequency synthesis is used.
The implemented divider in the feedback path of the synthesizer is carried out as a multi-modulus divider
(MMD). Also the 26 MHz reference signal serves as comparison frequency of the phase detector. The UMTS loop
filter is fully integrated and the loop bandwidth is about 180 kHz. The open loop gain is automatically adjusted
prior each UMTS channel programming.
The two fully integrated UMTS VCOs are designed for the UMTS bands (I, II, III, IV, V, VI, VIII, IX and X) and operates
at double (for bands I, II, III, IV, IX and X) or four times (for bands V, VI and VIII) of the transmit or receive
frequency. To cover the wide frequency range the VCOs are automatically aligned by a binary automatic band
selection before the settling process of the synthesizer starts.
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