LG F7100, Service Manual

Page: 16 / 126

3. TECHNICAL BRIEF
- 17 -
3.2 Power Amplifier Module (RF3133, U401)
The RF3133 is a high-power, high-efficiency power amplifier module with integrated power control.
The device is self-contained with 50
Ω input and output terminals. The power control function is also
incorporated, eliminating the need for directional couplers, detector diodes, power control ASICs and
other power control circuitry; this allows the module to be driven directly from the DAC output.
The device is designed for use as the final RF amplifier in GSM 850, E-GSM 900, DCS and PCS
handheld digital cellular equipment and other applications in the 824-849 MHz, 880-915 MHz, 1710-
1785 MHz, and 1850-1910 MHz bands.
On-board power control provides over 37 dB of control range with an analog voltage input
(TX_RAMP); and, power down with a logic “low” for standby operation (TX_ENABLE).
External control (BAND_SELECT) is used to select the GSM or DCS band with a logic high or low. A
logic low enables the GSM band whereas a logic high enables the DCS band.
Figure 3-5 Functional Block Diagram of RF3133