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AM79C02

Dual Subscriber Line Audio Processing Circuit (DSLAC™) Devices

Advanced Micro Devices 

Discrimination against 12 kHz and 16 kHz

Metering Signals

If the DSLAC device is used in a metering application

where 12 kHz or 16 kHz tone bursts are injected onto the

telephone line toward the subscriber, a portion of those

tones also may appear at the VIN terminal. These out-of-

band signals may cause frequency components to ap-

pear below 4 kHz at the digital output. For a 12 kHz tone,

the frequency components below 4 kHz are reduced

from the input by at least 48 dB, and for 16 kHz tones,

the components are reduced by more than 70 dB.

To avoid degradation of in-band transmission perfor-

mance, the input levels of these out-of-band tones

must be limited. The maximum allowable level is 100

mVrms at 12 kHz, and is 500 mVrms at 16 kHz. An

external notch filter at the VIN pin of the DSLAC device,

incorporated with the metering injection design, is ef-

fective in reducing these tone levels.

Spurious Out-of-Band Signals at the

Analog Output

With PCM code words representing a sine wave signal

in the range of 300 Hz to 3400 Hz at a level of 0 dBm0

applied to the digital input, the level of the spurious out-

of-band signals at the analog output is less than the

limits shown in the following table.

Frequency

4.6 kHz to 40 kHz

40 kHz to 240 kHz

240 kHz to 1 MHz

Level

–32 dBm0

–46 dBm0

–36 dBm0

With code words representing any sine wave signal in

the range 3.4 kHz to 4.0 kHz at a level of 0 dBm0 applied

to the digital input, the level of the signals at the analog

output are below the limits in Figure 6. The amplitude

of the spurious out-of-band signals between 3400 Hz

and 4600 Hz is given by the formula:

A = –14 – 14 sin π----(---f---–-----4---0---0---0---) dBm0

1200

0

–10

–20

Level (dBm0)

–30

–40

–50

DSLAC Device Specification

–28 dB

–32 dB

3.4

4.0

4.6

Frequency (kHz)

09875H-010

Figure 6. Spurious Out-of-Band Signals

SLAC Products

15

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