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5.2 RF
5.2.1 General
The RF-part is based on Hitachi dualband GSM RF-chip HD155121F, which
includes receiver circuit, offset loop modulation TX architecture and IF-VCO.
The final power amplifier is Hitachi PF08103B dualband TX module. RF parts
are powered by three 2.8V linear regulators, which provide separate power
supply for PLL synthesizer and VCO, modulator and TX-parts, and other RF-
parts such as AGC-amplifier and LNA etc.
5.2.2 Receiver
The incoming RX signal from antenna front-end switch X403 is fed via front
end filter X301 to the LNA-block, which consists of two amplifiers, one for each
band. After LNA-block RX signal is filtered again in filter X302 and applied to
the input of first mixer in the RF-chip where the signal is converted to first IF of
225MHz. The channel filtering is accoplished with first IF filter X303. After
filtering the signal is fed back to the RF-chip for second frequency conversion.
Second IF-frequency is 45 MHz. The second local oscillator signal and 45MHz
signal required for IQ demodulation is generated in RF-chip. Automatic Gain
Control (AGC) is made by changing the gain of both mixer stages and by
adjusting the gain of 45 MHz second IF-amplifier.
5.2.3 Transmitter
The TX signal is generated by dividing the 540 MHz IF-VCO frequency by 2 or
by 4. This 270 MHz signal ( 135 MHz in DCS-1800 band ) is then modulatid
with I and Q signals. The IQ modulated signal is fed to the phase comparator
where it is compared to the mixed signal of RF-VCO X304 and TX-VCO X401.
The phase comparator output is then filtered and applied to TX-VCO. This
architecture makes it possible to use oscillators running at final frequency.
Modulated RF-signal from TX-VCO is then amplified in dualband TX module
I405 and routed via antenna front-end switch X403 to the antenna connector.
The power control loop consists of directional coupler X402, detector diodes
D401 and comparator I404.
5.2.4 Synthesizer
RF-synthesizer, which controls RF-channel frequency, is made of serial
controlled dual synthesizer chip I304 and dualband VCO-module X304. IF-
synthesizer includes the same synthesizer chip I304 and IF-VCO, which is
integrated in Hitachi RF-chip, resonator circuits is excluded. Loopfilters of both
synthesizers are passive type. 13 MHz reference signal is generated in
VCTCXO module X1. The frequency of IF-synthesizer is switched 4 MHz
depending on TX / RX cycle and uset RF channel.
4c2300gb.fm
Product:TGP71EU & TGP73EU /
08.02.2002
OC2300
10
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