Motorola A920 Service Manual page 74

A920: Harmony Lite (TX Section)
TX_I+
TX_I-
WCDMA
TX
TX_Q+
TX_Q-
Description
The BBIF(BBIF_TX) is the transmit data path for transferring digitally sampled I / Q data from the POG. The demultiplexing unit performs the I/Q deinterleaving func-
tion to supply separate I and Q channel data into the transmit FIR filters. The FIR filter design is used to meet 3GPP spec requirements of simultaneous transmission of a
pilot channel and of multiple data channels each requiring a different spreading code and each requiring separate power control. The PN sequence generator provides I/Q
interleaved 8-bit PN data into the demultiplexing section. The DC correction(DCOC) block is able to correct for DC offsets due to the D/A's, anti-aliasing filters, and
transmit FIR filters in a feedback control loop. A mixed mode control loop located at the output of the transmit FIR filter is employed to correct DC offsets and I/Q gain
imbalances, i.e. DCOC and I/Q Phase and Gain equalizer. The outputs of the I/Q gain equalization unit is fed into 10-bit I and Q DAC's. The programmable gain anti-
aliasing filters, or TX smoothing filters, accepts differential I/Q signals of DC to 1.92MHz frequency components from the D/A Converters to attenuate the unwanted
clock signals of 15.36MHz and to smooth the signals for the TX modulator(MAX2363). The output of the TX smoothing filters are then fed into a multiplexed 6-bit A/D
with sample/hold scheme. This gives the information of the amplitude and the DC common mode voltage from the I / Q Tx filter outputs by a single Analog-to-Digital
Converter (ADC) as the part of digital correction loop.
The differential TX I and TX Q signal are finally fed into the TX modulator(MAX2363).
Mux
S/H
S/H
HARMONY LITE
(TX section)
Demux
10 bits
I/Q
Phase
Tracking
and
DCOC
Loop
Gain
10 bits
Equal
U101
PN Seq
Gen.
FIR
BBIF_TX
Demux
(9:0)
FIR
BBIF_TX_FRAME
BBIF_CLK
POG
U1000