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AD6472
–5–
Circuit Description
T he AD6472 is an HDSL analog front end for either 2-pair or
single pair applications.
T ransmit Channel
T he AD6472 receives, from a DSP transceiver core, a serial 2s
complement data stream. T he data are 16-bit words and the
MSB is received first.
T he 12-bit DAC converts the digital data to an analog signal.
Although HDSL uses four level 2B1Q modulation, the 12-bit
DAC is necessary because of the linearity requirements of the
echo canceling circuit.
T he active filters have dynamic tuning and selectable filter
corners that meet transmit mask requirements for both two-pair
and single pair applications. A 6 dB attenuation option is in-
cluded as part of the filter to increase the driver output dynamic
range. Bypassing the active filter means giving up the 6 dB
option, and reduces the maximum T X output voltage to
2 V p-p diff.
T he filtered transmit signal is then processed by the driver
amplifier. T he DAC output controls the driver output level.
T he designer can choose to bypass the driver amplifier; in this
case the driver amplifier will be powered down, and the T X
output will be at the T X _LPF_OUT pins.
T he AD6472 meets the requirements of the ET SI masks (both
frequency and time domains for pulse shape). T his includes the
worst case in RT R/T M 3036.
T able I. T ransmit Spectra
Rate
Kbps
Nyquist Frequency
kHz
T ime Interval
T (
m
s)
Application
1168
2320
2-Pair E1
Single Pair E1
292
580
1710
862
B
C
D
–0.4T
0.4T
A
F
–1.2T
–0.6T
0.5T
14T
50T
H
E
F
A
G
1.25T
PARAMETER
VALUE
%
A
B
C
D
E
F
G
H
0.0264
2.8248
2.64
2.4552
0.0792
–0.0264
–0.4224
–0.1320
1
107
100
93
3
–1
–16
–5
0
Figure 1. 2-pair Transmit Pulse Shape Mask Normalized
B
C
D
–0.4T
0.4T
A
F
–1.2T
–0.6T
0.5T
14T
50T
H
E
F
A
G
1.25T
PARAMETER
VALUE
%
A
B
C
D
E
F
G
H
0.0250
2.6750
2.500
2.3250
0.104
–0.0250
–0.5000
–1.250
1
107
100
93
4
–1
–20
–5
0
Figure 2. Single Pair Transmit Pulse Shape Mask Normalized
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