AFE1230

5

SBWS015A

Receive Filter

The receive filter consists of three independent sections used

for both the removal of quantization noise as well as the

reduction of data rate (otherwise known as downsampling).

downsampling ratio of 12x. The resulting digital signal is then

passed to a droop compensation filter before being sent

through the final IIR filter section, while being downsampled

by two. Two filter cutoff configurations are available, as seen

in Table II. The corresponding cutoff frequencies relate to the

full-rate low-pass filter spectral template of the filter, as seen

from the inputs of Table II.

Transmit Power

The on-chip differential line driver is designed to drive G.SHDSL

power levels directly, or it can be used as a low-power buffer for

driving a higher power external driver (for example the OPA2677)

for applications such as HDSL2. The AFE1230 driver will

generate an output swing of 6.2V peak-to-peak differential.

When used with a suitable transformer (see Figures 8 and 10),

the AFE1230 can generate up to 14.5dBm of power into a 135

Ω

line load. When used as a buffer with an OPA2677 driver,

17dBm of power can be generated. Relative transmit power can

be controlled digitally through control bits sent to the transmit

section by the serial interface. Relative transmit power reduction

can be set to 0, –6, –12, or –18dB, depending on the control bits

presented to the AFE1230, as shown in Table III.

FIGURE 2. Overall Transmit Filter. D/A Converter Frequency Response, Fifth-Order with 0.25x, 0.38x, and 0.5x.

FIGURE 3. Overall Transmit Filter. D/A Converter Frequency Response, Seventh-Order with 0.25x, 0.38x, and 0.5x.

TABLE III. Transmit Power Backoff.

TABLE II. rx Filter Cutoff Frequency Setting.

rx CUTOFF (txData Bit 24)

RATIO (Corner Frequency)

0

0.25 MCLK/24

1

0.5 MCLK/24

TRANSMIT POWER

TRANSMIT

BACK OFF CODE

POWER

TRANSMIT POWER

(txData Bits 25, 26)

REDUCTION

G.SHDSL

HDSL2

00

0dB

14.5dBm

17.0dBm

01

–6dB

8.5dBm

11.0dBm

10

–12dB

2.5dBm

5.0dBm

11

–18dB

–4.5dBm

–1.0dBm

0

–50

–100

–150

–200

–250

–300

0

–50

–100

–150

–200

–250

–300

–350