Umts Transmitter - LG -V909DW Service Manual

3. TECHNICAL BRIEF

3.3.2 UMTS TRANSMITTER

The Tx paths share a common interface from the Tx DAC, and then they share the RF transmitter's analog
baseband circuits. Each band category, low and high, has a dedicated baseband-to-RF upconverter and its
own set of RF gain stages. A single RF Tx power-detector circuit is integrated on-chip and supports all CDMA
bands (only one output is active at a time).
The RF transmit paths begin with a single, shared analog I and Q differential baseband signal from the
device's baseband circuits. Each component of the baseband signal is lowpass filtered and amplified to levels
sufficient for driving the quadrature upconverters. Only one upconverter is active at a time. The active
upconverter's output is at the desired RF channel frequency, and drives its dedicated output circuits. These
RF circuits include multiple variable gain stages that provide transmit AGC control. The wide range of driver-
amplifier output levels is achieved while supporting the UMTS standard's requirements for ACLR, spurious
emissions, Rx-band noise, etc. All transmitter output ports are single-ended with 50-Ohm nominal
impedance. Each requires a simple matching network to interface with its RF front-end circuits' Tx path. The
driver amplifiers end the signal-path circuitry within the MDM device, but the external transmit paths needed.
[Figure 3-9] 3G transiever path
[Figure 3-10] 3G transiever internal block
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