Tdma 1900 Rx; Frequency Synthesizers - Nokia NSW-5 Series Service Manual

PAMS Technical Documentation
The received RF signal from the antenna is fed through a duplex filter to
the receiver unit. The signal is amplified by a low noise preamplifier. In
digital mode the gain of the amplifier is controlled by the AGC2 control
line. The nominal gain of 15 – 20 dB is reduced in the strong signal
condition about 14 – 19 dB (in digital mode). After the preamplifier the
signal is filtered with a SAW RF filter. The filter rejects spurious signals
coming from the antenna and spurious emissions coming from the mixer
and IF parts.
The filtered RF–signal is downconverted by an active mixer. The fre-
quency of the first IF is 116.19 MHz. The first local signal is generated in
the UHF synthesizer. The IF signal is fed through a SAW IF–filter. The
filter rejects intermodulating signals and the second IF image signal. The
filtered 1st IF is fed to the receiver section of the integrated RF circuit
EROTUS, which has separate IF paths for analog and digital modes of
operation.
In digital mode the IF1 signal is amplified by an AGC amplifier, which has
a gain control range of 57 dB. The gain is controlled by an analog signal
with AGC1–line. The amplified IF signal is down converted to a second
IF in the mixer of EROTUS. The second local signal is the 6th overtone of
the 19.44 MHz VCTCXO. LO frequency multiplier is implemented in two
stages. First multiplication by 3 is done with a EROTUS multiplier with an
external trap and the second multiplication by 2 is done in the integrated
doubler in EROTUS.
The second IF frequency is 450 kHz. The second IF is filtered by two ce-
ramic filters. The filter rejects signals on the adjacent channels. The fil-
tered second IF is fed back to EROTUS, where it is amplified and fed
balanced out to COBBA_D via IF2D lines.
In analog mode the filtered and amplified IF1 signal is fed to a mixer. This
mixer has been optimized for low current consumption. After this the
mixer down converted signal is fed through the same IF2 filter as in digital
mode and finally it is amplified in the limiter amplifier. The limited IF2 sig-
nal is fed via balanced IF2A lines to COBBA_D, which has a digital FM–
detector. The limiter amplifier produces also a RSSI voltage for analog
mode field strength indication.

TDMA 1900 RX

On 1900 MHz band the receiver operates only in digital mode. There is a
separate front end for this band. IF–parts are common for both bands.
Operation of the receiver is similar to digital mode operation on 800 MHz
band.

Frequency Synthesizers

The stable frequency reference for the synthesizers and base band cir-
cuits is a voltage controlled temperature compensated crystal oscillator
VCTCXO. Frequency of the oscillator is 19.44 MHz. It is controlled by an
Issue 1 10/00
E Nokia Mobile Phones Ltd.
NSW-5
System Module UT5U
Page 35