Nokia NHM-8NX Series Troubleshooting Instructions page 20

NHM-8NX
Troubleshooting Instructions
2
RX
L704
GSM
TX
Dir.
RX
Coupler
L709
PCN
TX
RX/TX
Z700
DET
PLL
The PLL supplies Local Oscillator (LO) signals for the RX and TX-mixers. In order to be able
to generate LO-frequencies for the required EGSM and PCN channels a regular synthe-
siser-circuit is used. All blocks for the PLL except for the VCO, reference X-tal and loopfil-
ter is located in the Mjoelner IC.
The reference frequency is generated by a 26MHz Voltage Controlled X-tal Oscillator
(VCXO) which is located in the Mjoelner IC. Only the X-tal is external. 26MHz is supplied
to BB where a divide-by-2 circuit (located in the UPP IC) generates the BB-clock at
13MHz. The reference frequency is supplied to the reference divider (RDIV) where the
frequency is divided by 65. The output of RDIV (400kHz) is used as reference clock for the
Phase Detector (ϕ).
The PLL is a feedback control system controlling the phase and frequency of the LO-sig-
nal. Building blocks for the PLL are: Phase detector, Charge Pump, Voltage Controlled
Oscillator (VCO), N-Divider and loopfilter. As mentioned earlier only the VCO and loopfil-
ter is external to the Mjoelner IC.
The VCO (G600) is the component that actually generates the LO-frequency. Based on
the control voltage input the VCO generates a single-ended RF output. The signal is then
differentiated through a balun. This signal is fed to the Prescaler and N-divider in Mjoel-
ner, these 2 block will together divide the frequency by a ratio based on the selected
channel. The divider output is supplied to the phase detector which compares the fre-
quency and phase to the 400kHz reference clock. Based on this comparison the phase
Page 20
Figure 2: Transmitter signal path
VANTL / VANTM
VANTH
2
VB_DET
VTXLOL
VTXLOH
VTXBH
VTXBL
PCN
V701
Balun
Buffer
VTX
PA
SAW
N700
Z603
Buffer
EGSM
V702
DET
PW-
PLFB1
loop
PLFB2
filter
VPCH/VPCL
2
VBATTRF
ãNokia Corporation
PAMS Technical Documentation
VDDDIG
RF
Controls
1/2
VDDRXBB
RF
Controls
2
OUTHP
OUTHM
OUTLP
OUTLM
PWC
Supply
filter
TX
TX
VR2
P C
Mjoelner
N600
1/4
2
2 2
2 2
Issue 1 05/02