V1.20 Page 11 of 48 ICM MP CCQ GRM
A55/C55_Hitachi Company Confidential © Copyright Siemens AG 04/03
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.
(RF Control J15, J16, J17) is used. To ensure
the frequency stability, the 640MHz VCO signal is compared by the phase detector of
the 2
nd
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
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