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4.2.3
Synthesizer: LO2
The second local oscillator is required for transmitter operations only. It consists of a
PLL and a VCO which are integrated inside the Bright 4, and an external second order
loopfilter
(R831; C830;
C832). Before the VCO generated 640 or 656MHz signal
arrives at the modulator, it is divided by 8. So the resulting frequency after the IQ
modulator is 80/82MHz (dependent on the channel and band). Programming of the
LO2 PLL is done in the same way as described at the LO1 the tree-wire-bus
(EGOLD+ signals RFDATA; RFCLK; RFSTR.
is used. To ensure
(RF Control J15, J16, J17)
the frequency stability, the 640MHz VCO signal is compared by the phase detector of
nd
the 2
PLL with the 26Mhz reference signal. The resulting control signal passes the
external loop filter and is used to control the 640/656MHz VCO.
The required voltage
VCC_SYN
is provided by the ASIC
D361
Circuit diagram
Loop-filter LO2
V1.20
Page 11 of 48
ICM MP CCQ GRM
A55/C55_Hitachi
Company Confidential © Copyright Siemens AG
04/03
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