Nokia NHL-2NA Series, Troubleshooting Instructions, Page: 71 / 148

CCS Technical Documentation
NHL-2NA
Issue 1 07/02 ¤ Nokia Corporation Page 5
baseband filter inside HAGAR is an active-RC-filter with two off-chip capacitors. Large
RC-time constants are needed in the channel select filter of the direct-conversion
receiver and are achieved with large off-chip capacitors because the impedance levels
could not be increased due to the noise specifications.
The baseband filter consists of two stages, DTOS and BIQUAD. DTOS is differential to sin-
gle-ended converter having 8dB or 18dB gain. BIQUAD is modified Sallen-Key Biquad.
Integrated resistors and capacitors are tunable. These are controlled with a digital con-
trol word. The correct control words that compensate for the process variations of inte-
grated resistors and capacitors and of tolerance of off chip capacitors are found with the
calibration circuit.
The next stage in the receiver chain is AGC-amplifier, also integrated into HAGAR. AGC
has digital gain control via serial mode bms. AGC-stage provides gain control range (40
dB, 10 dB steps) for the receiver and also the necessary DC compensation. Additional 10
dB AGC step is implemented in DTOS stages.
DC compensation is made during DCN1 and DCN2 operations ( controlled via serial bus ).
DCN1 is carried out by charging the large external capacitors in AGC stages to a voltage
which effect a zero dc-offset. DCN2 set the signal offset to constant value ( V
ref
RF_02
1.35 V ). The V
ref
RF_02 signal is used as a zero level to RX ADCs.
Single ended filtered I/Q-signal is then fed to ADCs in BB. Input level for ADC is 1.45 V
pp
max.
Rf-temp port is intended to be used for compensation of RX SAW filters thermal behav-
ior. This phenomena will have impact to RSSI reporting accuracy. The current information
is -35ppm/C for center frequency drift for all bands. This temperature information is a
voltage over two diodes and diodes are fed with constant current.
E-GSM900
E-GSM900 RX Troubleshooting Setup steps
1 Place the phone in the test jig
2
7
6
5
4
3
Maintenance
→
Testing
→
RF Controls
Set Active unit to 'Rx'
Set Operation mode to 'Continuous'
From 'Toolbar' set operating mode to Local
File
→
Choose Product
→
Calypso
Select band 'GSM900'
Set Rx/Tx channel to 37
Set AGC to '8:FEG ON +46 dB'
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