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3. TECHNICAL BRIEF
LGE Internal Use Only
3.14.1.2 Transmit Path
Overview
The transmit section of the AD6548/9 radio implements a translation loop modulator.
This consists of a quadrature modulator, high speed phase-frequency detector (PFD)
with charge pump output, loop filter, TX VCO and a feedback down converting
mixer. The VCO output (divided by 2 for low band) is fed to the power amplifier with a
portion internally fed back into the down-converting feedback mixer to close the
feedback loop.
Quadrature Modulator
The Quadrature modulator takes the baseband I & Q signals and translates these into
a GMSK signal at the Transmit Intermediate Frequency (TX IF). After bandpass
filtering and limiting the TX IF signal is used as the reference input to the Phase
Frequency Detector (PFD) of the transmit PLL.
Figure. 3-14-3 Transmit Path Block Diagram