Only For Training And Service Purposes - LG GT500 Service Manual

• The combined DAC and LP filter is used to convert the digital words of the digital block into analog signals.
The LP filters are 3rd order Bessel reconstruction filters.
• The second FM path is used to add the high-frequency part of the FM to the VCO. It also includes an auto-
tuning block that compensates for VCO gain variations.
• The AM block converts the differential voltage from the DAC to a single-ended output that drives the PA. The
output is scaled according to the desired output power, and an offset can be added for PA linearization.
• The Tx-buffer is used to drive the PA with the correct power level. A divide by 2 or 4 block is used to generate
the correct output frequency from the 4 GHz VCO.
WCDMA Transmitter Block
The transmitter has differential voltage I and Q inputs. The IQ signal is filtered in a second order LP filter before
it is up-converted to the RF in the direct IQ mixer. Automatic trimming of the filter RC constant ensures that the
bandwidth variation is sufficiently low.
The signal path is split in one low and three high band paths. The RF signal is amplified in a PGA, which is
controlled by the 3-wire control bus. The low band and two of the high band transmit output stages provide
+5 dBm (minimum) and the last high band output stage provide +7 dBm (minimum) at maximum power
control. The output power is set
through the serial bus.
3.7.3.2. Receiver part
Receiver
The receiver is a homodyne receiver with direct conversion of the received radio channel to baseband I and Q
channels.
The receiver block consists of multi-band front ends with separate LNAs, a common mixer and a common LP
filter with configurable bandwidth.
GSM/EDGE Receiver
The front end block is followed by a baseband block with active anti-aliasing filters that also suppress blocking
signals and interferers. Automatic trimming of the filter RC constant ensures that the bandwidth variation is
sufficiently low. The baseband block is followed by a fully integrated ADC of sigma delta structure with high
dynamic range. The analog signals are converted to digital bit-streams in a sigma delta converter. The digital
output signals are sent over a serial interface to the digital baseband controller for further processing and
detection.
WCDMA Receiver
The front end block is followed by a baseband block with active anti-aliasing filters that suppress blocking
signals and interferers. Automatic trimming of the filter RC constant ensures that the bandwidth variation is
sufficiently low. The baseband signal is amplified in a PGA, which is controlled by the 3-wire control bus. The
PGA has a built in second order loop for DC-offset cancellation. The output of the receiver is analog differential
I, Q signals.
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Only for training and service purposes

3. TECHNICAL DESCRIPTION
- 69 - LGE Internal Use Only