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GSM
PCN
Mechanical
Diplexer
Switch
GSM RX = 935-960Mhz
PCN RX =1805-1880Mhz
External RF
The rf signals from L305 form the inputs to the active double-balanced rf mixer of
IC300 #13-#14. These are mixed with the UHF VCO (GSM 1205Mhz-1230Mhz,
PCN 1535Mhz -1610Mhz) which is input to IC300 #17-18. When these two rf
signals are mixed a resultant signal of 270Mhz is produced, this is the
intermediate frequency (IF). The signal RX_ON2 (derived from IC27-#28) is the
control input which enables the mixer. Outputs from the mixer are differential with
the signals phase shifted by + and - 90 degrees. These are then fed into a Dual IF
SAW filter (FL304) and then back into IC300 #8-#9.
The RX IF of 270Mhz has been selected based on the number of image response
and intermodulation products in the IF band, subject also to the constraints that
harmonics of the IF do not fall within any RX and TX band and harmonics of the
13Mhz TCXO do not fall in the IF band.
The differential IF signal is then fed to the IF amplifier, within IC300 (see figure.3:
The IF Amp and demodulator). The gain of the amplifier is controlled by the
Superchip – IC27, using 3 AGC Control lines:
SYGCDT: AGC Programming Data Line (#75)
PGCSTR: AGC Programming Enable Line (#72)
SYGCCL: AGC Programming Clock Line (#74)
These signals are output from IC27 on the logic board. The IF amp can be
programmed to a range of 0dB to 70dB in 2dB steps, some 36 levels.
Fig.1: The Receiver
V_G_LNA
29
FL303
FL300
FL301
LNA
V_P_LNA
RX_ON2
27
15
270Mhz
LNA
LNA
26
20 21
13
17
FL302
L305
PMB2410
(IC300)
To IF Amp
8 9
FL304
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