AD6472

–5–

REV. 0

Circuit Description

The AD6472 is an HDSL analog front end for either 2-pair or

single pair applications.

Transmit Channel

The AD6472 receives, from a DSP transceiver core, a serial 2s

complement data stream. The data are 16-bit words and the

MSB is received first.

The 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.

The 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 TX output voltage to

2 V p-p diff.

The filtered transmit signal is then processed by the driver

amplifier. The DAC output controls the driver output level.

The designer can choose to bypass the driver amplifier; in this

case the driver amplifier will be powered down, and the TX

output will be at the TX_LPF_OUT pins.

The AD6472 meets the requirements of the ETSI masks (both

frequency and time domains for pulse shape). This includes the

worst case in RTR/TM 3036.

Table I. Transmit Spectra

Rate

Nyquist Frequency

Time Interval

Kbps

Application

kHz

T ( s)

1168

2-Pair E1

292

1710

2320

Single Pair E1

580

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