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RF OVERVIEW
MCUK990801G8
Section 3
Issue A
Technical Guide
– 15 –
Revision 0
Figure 3.2: GSM 900 Frequency Plan
Figure 3.3: GSM 1800 Frequency Plan
3.2.2 General
The major building blocks for the RF design are the Hitachi transmit (Tx) and receive (Rx) IC, Fujitsu RF-IF dual PLL and the
antenna subsystem.
In either receiver band, GSM900 or GSM1800, the Rx 1st IF is fixed at 225 MHz and 2nd IF at 45 MHz. Therefore, the 2nd
local oscillator is fixed at 540 MHz for receive mode.
In GSM900 transmit mode, the 2nd LO is reprogrammed to 540 MHz, the same for receive mode.
In GSM1800 mode, the 2nd local oscillator is re-programmed to 520 MHz. For this choice of IF, no transmitter in-band spurious
is believed to occur due to harmonics of the 1st LO.
The Tx VCO will be on-channel in either GSM900 or GSM1800 modes of operation.
935-960MHz
RF LO
1160-1185MHz
TX VCO
890-915MHz
Fcomparison
270MHz
Fdiff
270MHz
Rx 1st IF
225MHz
IF LO
VCO
540MHz
Rx 2nd IF
45MHz
÷2
45MHz
270MHz
I
Q
I
Q
÷2
÷6
90MHz
÷2
270MHz
10077-1
1805-1880MHz
RF LO
1580-1655MHz
TX VCO
1710-1785MHz
Fcomparison
130MHz
Fdiff
130MHz
Rx 1st IF
225MHz
IF LO VCO
Rx: 540MHz
Tx: 520MHz
Rx 2nd IF
45MHz
÷2
45MHz
270MHz
I
Q
I
Q
÷2
÷6
90MHz
÷2
260MHz
10078-1
