LG U8130 Service Manual page 75

3. TECHNICAL BRIEF
B. Receiver Block.
The circuit contains one frequency down-conversion section for each receive band and a common
base band amplifier and filter section. The GSM900 RF part consists of a low noise amplifier followed
by high dynamic range mixers.
The DCS 1800 RF part also has low noise amplifier connected to the other mixers.
The amplified RF signal is mixed with the quadrature local oscillator signal to create in-phase (I) and
quadrature phase (Q) baseband signals. The I and Q signals are then buffered and low pass filtered.
The same baseband circuitry is used for all bands.
Balanced signals are used for minimizing cross talk due to package parasitics. An impedance level at
RF of 150 ohms for the GSM 900 input and 50 ohms for the DCS 1800 input is chosen to minimmize
current consumption at best noise performance.
The low gain mode in GSM 900 is used in high input signal mode. There is no gain switch in DCS
1800.
Figure 3-3 shows a block diagram of the receiver block.
Figure 3-3. Block diagram of receiver part.
- 76 -