NHM–7
System Module & UI
PAMS Technical Documentation
Page 36
Issue 1 10/2001
Nokia Corporation
DC compensation is made during DCN1 and DCN2 operations (controlled
via serial bus). DCN1 is carried out by charging the large external capaci-
tors in AGC stages to a voltage which cause a zero dc–offset. DCN2 set
the signal offset to constant value (VrefRF_02 1.35 V). The VrefRF_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 Vpp max.
Rf–temp port is intended to be used for compensation of RX SAW filters
thermal behavior. This phenomena will have impact to RSSI reporting ac-
curacy. 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.
Transmitter
Transmitter chain consists of two final frequency IQ–modulators for upper
and lower band, a dual power amplifier and a power control loop.
I– and Q–signals are generated by baseband. After post filtering (RC–net-
work) they go into IQ–modulator in HAGAR. LO–signal for modulator is
generated by VCO and is divided by 2 or by 4 depending on system
mode. There are separate outputs one for EGSM and one for GSM1800.
In EGSM branch there is a SAW filter before PA to attenuate unwanted
signals and wideband noise from the Hagar IC.
The final amplification is realized with dual band power amplifier. It has
two different power chains one for EGSM and one for GSM1800. PA is
able to produce over 2 W (0 dBm input level) in EGSM band and over 1
W (0 dBm input level) in upperband band into 50 ohm output . Gain con-
trol range is over 45 dB to get desired power levels and power ramping
up and down.
Harmonics generated by the nonlinear PA are filtered out with filtering in-
side the antenna switch –module.
Power control circuitry consists of discrete power detector (common for
lower and upperband) and error amplifier in HAGAR. There is a direction-
al coupler connected between PA output and antenna switch. It is a dual-
band type and has input and outputs for both systems. Dir. coupler takes
a sample from the forward going power with certain ratio. This signal is
rectified in a schottky–diode and it produces a DC–signal after filtering.
The possibility to improve efficiency in low power levels has been speci-
fied in power amplifier module. The improved efficiency will take place on
power level 7 and lower in EGSM. For this option there is control input
line in PA module.
AFC function
AFC is used to lock the transceivers clock to frequency of the base sta-
tion. AFC–voltage is generated in BB with 11 bit DA–converter. There is a
Summary of Contents for NHM-7 series
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