Only For Training And Service Purposes - LG -S310 Service Manual

Phase Frequency Detector (PFD)
3. TECHNICAL BRIEF
This ensures that the transmitted signal is accurately locked to the desired frequency with the desired TX
phase modulation. The downconverted feedback signal from the PA is phase locked to the reference
quadrature modulator output by the PFD charge pump output supplying current to the loop filter. The filter
is autocalibrated together with the RX baseband filters to remove any process tolerances.
TX VCO
The Transmit Voltage Controlled Oscillator (TX VCO) and tank components are a fully integrated subsystem.
The subsystem includes PA drivers so the outputs are used to directly drive the external PAs. In Low band
operation the TX VCO output is divided by two and filtered.
Feedback Path
The feedback path is modified from the standard GMSK Translational loop, by inclusion of the Power
Amplifier (PA), as shown in Figure 4.2.2-1. This enhancement means the loop corrects for AM to PM distortion
that is generated in the PA with non constant-envelope modulation. The feedback signal is coupled from the
PA output and applied to a successive detection log/limiting amplifier. The limiting function removes the
amplitude information from the feedback and applies the phase information to the translational loop via the
feedback down converting mixer. The detector output is used in the AM loop. The feedback down converting
mixer is used to translate the amplitude limited feedback signal to the TX IF Frequency. The subsequent
integrated band pass filter removes the mixers unwanted side band and higher order mixing products, prior
to the PFD input. A Fully integrated TX Sequencer manages phase locking prior to PA ramping.
AM Loop
The Polar modulator architecture also contains an amplitude loop for control of the PA output power. This
allows the AM content of the 8PSK modulation to be efficiently and accurately transmitted by a Polar PA
significantly exceeding spectral mask requirements. Non linear and distortion effects created in the PA are
automatically corrected by the loop, enabling ease of use in operation and minimal factory calibration.
The Output of the Modulator is fed to a high dynamic range Log Detector. The detector extracts the AM
content from the modulator output, which is used as the reference in the AM loop. The feedback path
consists of a coupler on the PA output and a high dynamic range matched Log Detector. Both signals are fed
to the Amplitude controller block.
The Amplitude controller block takes inputs from both the Reference and Feedback Detectors and from the
RAMP input terminal. Using various signal processing techniques an error term is generated which is fed into
an integrator. The integrator output voltage is used to drive the PA Power control input pin. To support a
variety of PA models the Amplitude Controller gain slope can be programmed via the serial bus. The
amplitude controller includes a DAC for precise alignment of the feedback path loop. This is achieved by a
onetime simple factory power calibration procedure. Unwanted amplitude variations in the reference path
(eg. IQ input level) are removed by a track and hold circuit integrated into the Amplitude Controller block. In
GMSK mode the reference detector circuit is powered down, but the RAMP input remains active meaning no
external circuitry or switching is required for PA control in ether mode.
LGE Internal Use Only
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Only for training and service purposes