Nokia 5140 Manuales De Servicio
Nokia Customer Care
System Module and User Interface
NPL-4/5
Issue 1 05/04
Copyright © 2004 Nokia Corporation. All rights reserved.
Page 81
shifting by 90 degrees which is needed for the demodulator mixers.
The demodulator output signals are all differential. After the demodulators the amplifiers
convert the differential signals to single ended. Before that, they combine the signals
from the three demodulators to a single path which means that from the output of the
demodulators to the baseband interface there are just two signal paths (I and Q) which
are common to all the frequency bands of operation.
convert the differential signals to single ended. Before that, they combine the signals
from the three demodulators to a single path which means that from the output of the
demodulators to the baseband interface there are just two signal paths (I and Q) which
are common to all the frequency bands of operation.
In addition, the amplifiers perform the first part of the channel filtering and AGC: they
have two gain stages, the first one with a constant gain of 12 dB and 85 kHz -3 dB
bandwidth and the second one with a switchable gain of 6 dB and -4 dB. The filters in
the amplifier blocks are active RC filters. The rest of the analog channel filtering is pro-
vided by blocks called BIQUAD.
have two gain stages, the first one with a constant gain of 12 dB and 85 kHz -3 dB
bandwidth and the second one with a switchable gain of 6 dB and -4 dB. The filters in
the amplifier blocks are active RC filters. The rest of the analog channel filtering is pro-
vided by blocks called BIQUAD.
After the amplifier and BIQUAD blocks there is another AGC-amplifier which provides a
gain control range of 42 dB in 6 dB steps.
gain control range of 42 dB in 6 dB steps.
In addition to the AGC steps, the last AGC stage also performs the real time DC offset
compensation which is needed in a direct conversion receiver.
compensation which is needed in a direct conversion receiver.
After the last AGC and DC offset compensation stages the single ended and filtered I-
and Q-signals are finally fed to the RX ADCs. The maximum peak-to-peak voltage swing
for the ADCs is 1.45 V.
and Q-signals are finally fed to the RX ADCs. The maximum peak-to-peak voltage swing
for the ADCs is 1.45 V.
In the Helgo there is a port called RF-temp which can be used for compensation of RX
SAW filters thermal behavior. The temperature information to the Helgo comes from a
voltage over two diodes when the diodes are fed with temperature independent, con-
stant current.
SAW filters thermal behavior. The temperature information to the Helgo comes from a
voltage over two diodes when the diodes are fed with temperature independent, con-
stant current.
Transmitter
The transmitter consists of two final frequency IQ-modulators and power amplifiers, for
the lower and upper bands separately, and a power control loop. The IQ-modulators are
integrated in the Helgo, as well as the operational amplifiers of the power control loop.
The two power amplifiers are located in a single module which also includes the power
detector circuitry. Loop filter parts of the power control loop are implemented as dis-
crete components on the PWB. In the GMSK mode the power is controlled by adjusting
the DC bias levels of the power amplifiers.
the lower and upper bands separately, and a power control loop. The IQ-modulators are
integrated in the Helgo, as well as the operational amplifiers of the power control loop.
The two power amplifiers are located in a single module which also includes the power
detector circuitry. Loop filter parts of the power control loop are implemented as dis-
crete components on the PWB. In the GMSK mode the power is controlled by adjusting
the DC bias levels of the power amplifiers.
The modulated waveforms, i.e. the I- and Q-signals, are generated by the baseband part
of the engine module. After post filtering, implemented as RC-networks, they go into the
IQ-modulator. Local oscillator signals for the modulator mixers are generated by an
external VCO the frequency of which is divided by two in GSM1800 and in GSM1900 and
by four in GSM850/EGSM900. Those frequency dividers are integrated in the Helgo and
in addition to the division they also provide accurate phase shifting by 90 degrees which
is needed for the modulator mixers.
of the engine module. After post filtering, implemented as RC-networks, they go into the
IQ-modulator. Local oscillator signals for the modulator mixers are generated by an
external VCO the frequency of which is divided by two in GSM1800 and in GSM1900 and
by four in GSM850/EGSM900. Those frequency dividers are integrated in the Helgo and
in addition to the division they also provide accurate phase shifting by 90 degrees which
is needed for the modulator mixers.
At the upper band there is a dual mode buffer amplifier at the output of the IQ-modula-
tor.
tor.
The final amplification
is realized by a three stage power amplifier.