Transmitter - Nokia NSB-5 Series Technical Documentation Manual

NSB-5
System Module
The bandpass filtered signal is fed back to CRFU_2a, where the signal is down converted
with a double balanced active mixer (Gilbert cell) to 487 MHz. The local oscillator signal
for this down conversion is generated by the UHF VCO (G700) and buffered in CRFU_2a.
The first IF signal is bandpass filtered with SAW filter, which has external matching net-
works in both ends. This filter attenuates the intermodulating and image frequencies. The
second down conversion (occurs in CRFU_2a) results in a balanced IF of 87 MHz, which
is filtered using an 87 MHz SAW filter (Z700). This filter provides selectivity for channels
greater than +/– 200 kHz, and attenuates the image frequency of the third mixer and
intermodulating signals. The local oscillator signal for this down conversion is 400 MHz,
which is generated by the 800 MHz VHF VCO module (G702). The VHF VCO signal is buff-
ered and divided in SUMMA and the 400 MHz resulting signal is again buffered in
CFRU2a before the mixer.
After the 87 MHz filter, the signal is fed into the AGC amplifier which has been inte-
grated into SUMMA. The AGC amplifier contains analog gain control which provides
accurate gain control (minimum 57 dB) for the receiver. Control voltage for the AGC is
generated by the D/A converter in COBBA_GJP (N300). The final mixing stage occurs in
SUMMA with a local oscillator signal of 100 MHz generated by dividing the VHF–synthe-
sizer output (800 MHz) by eight.
The third (final) IF filter (Z701) is a ceramic bandpass filter with a center frequency of
13 MHz. This filter attenuates adjacent channels with very little attenuation for +/–
200 kHz. The +/– 200 kHz interferers are filtered digitally by DSP. The 13 MHz bandpass
signal is converted to a balanced signal with a buffer circuit in SUMMA. This buffer cir-
cuit has a voltage gain of 36 dB. This balanced signal is then fed to COBBA_GJ. The PGA
stage in COBBA_GJP has a gain setting of either 0 dB or 9.5 dB, which is controlled via
the COBBA_GJP control bus. For HD955 the PGA gain will be set to 0dB.

Transmitter

Transmitter chain consists of IQ–modulator, upconversion mixer, TX filter, TX buffer, and a
poweramplifier.
The differential I and Q signals are generated by COBBA_GJP and are filtered by an exter-
nal RC network (R501, R504, R505, R506, R514, R517, C525 and C526, fc=200kHz)
before being fed into the IQ modulator in SUMMA (N700). The modulator generates a TX
IF of 400 MHz, which is derived from the VHF synthesizer output (divide by two). Inside
SUMMA the 400 MHz is amplified and then fed to an external filter before being upcon-
verted in CRFU_2a. The upconverter in CRFU_2a is a double balanced image rejection
mixer. The local oscillator signal for the upconversion is generated by the UHF synthe-
sizer.
After CRFU_2a there is SAW filter (Z503) to attenuate the spurious signals generated in
the upconversion mixer in CRFU_2a.
After SAW filter TX–signal is amplified in discrete bufferstage that has 10 dB gain. Fol-
lowing discrete TX–buffer is a 3-pole ceramic bandpass filter (Z603), which attenuates
the image frequency, LO leakage, and wideband noise.
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Nokia Mobile Phones Ltd.
PAMS Technical Documentation
Issue 1 03/01