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Am79Q02/021/031 Data Sheet
Discrimination against 12- and 16-kHz Metering Signals
If the QSLAC 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 may also appear at the VIN terminal. These
out-of-band signals may cause frequency components to appear below 4 kHz at the digital output. For a 12 kHz or
16 kHz tone, the frequency components below 4 kHz will be reduced from the input by at least 70 dB. The sum of
the peak metering and signal voltages must be within the analog input voltage range.
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 below.
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:
Frequency
Level
4.6 kHz to 40 kHz
–32 dBm0
40 kHz to 240 kHz
–46 dBm0
240 kHz to 1 MHz
–36 dBm0
A14
–
14
π f4000
–
()
1200
----------------------------dBm0
sin
–
=
0
–10
–20
–30
–40
–50
–28 dB
–32 dB
QSLAC Device Specification
Frequency (kHz)
3.4
4.0
4.6
19256A-013
Level (dBm0)
Figure 6. Spurious Out-of-Band Signals
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