MT88E46 Ver la hoja de datos (PDF) - Zarlink Semiconductor Inc
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MT88E46 Datasheet PDF : 23 Pages
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MT88E46
Data Sheet
demodulation is available only at the Tip/Ring
connection. The CAS detector operates in ‘on hook mode’
and ‘off hook mode’ using different algorithms optimized
for the CPE states. On hook mode is available only at the
Tip/Ring connection, while off hook mode is available
only at the 4-wire side connection.
The ‘off hook mode’ is Bellcore compliant when the near
end speech is attenuated 8dB or better. It should be used
when the CPE is off hook. The ‘on hook mode’ is
optimized for talkdown only and typically meets talkdown
condition 1 (the average case) without near end speech
attenuation to provide Tip/Ring CAS detection for the on
hook state MEI CPE. It should be used when the CPE
itself is on hook but the line is in use.
The FSK demodulator is suitable for both Bell 202 and
CCITT V.23 formats transparently, and is compatible with
Bellcore and TIA standards. The demodulated FSK data is
either output directly (bit stream mode) or stored in a one
byte buffer (buffer mode) which can be shifted out. In the
buffer mode, the stop bit immediately following a byte is
also stored and can be shifted out after the data byte. This
facility allows for framing error checking as required in
TIA/EIA-777 for the Type 2 CPE. In the bit stream mode,
two timing signals are provided. One indicates the bit
sampling instants of the data byte, the other the end of the
byte. A carrier detector indicates the presence of signal
and shuts off the data stream when there is no signal.
The entire chip can be put into a power down mode
consuming virtually no power supply current. The input
op-amps, FSK demodulator, CAS detector and the
oscillator are all shut off. Furthermore, partial power
down has been incorporated to minimize the operating
current: when FSK is selected, the CAS detector is
powered down; when CAS is selected, the FSK
demodulator is powered down. The two input op-amps are
not affected by partial power down and will remain
operational regardless of whether FSK or CAS is selected.
Preliminary Off Hook Mode CAS Detector
Speech Immunity Performance
Since there is some randomness in speech immunity
testing, and because the telephone hybrid / speech IC
design will affect the result, the preliminary test results in
Tables 3 and 4 are provided to illustrate typical
performances only.
Condition 1
Condition 2
Condition 3
Condition 1
Condition 2
Condition 3
SR-TSV-002476
Requirement
Test Result for 0 dB
Near End Speech
Attenuation using
Pre-emphasized
Speech only
Test Result for 0 dB Near
End Speech Attenuation
using Pre-emphasized
Speech for Near End,
Normal Speech for Far
End
Test Result for 6 dB Near
End Speech Attenuation
using Pre-emphasized
Speech only
Vdd = 5V ± 10%, GS2 gain = 0dB
1 in ≥ 45 hours
1 in 48.0 hours
1 in 96.0 hours
1 in 96.0 hours
1 in ≥ 10 hours
1 in 8.6 hours
1 in 10.1 hours
1 in 16.5 hours
1 in ≥ 35 hours
1 in 37.4 hours
1 in 43.0 hours
1 in 113.1 hours
Vdd = 3V ± 10%, GS2 gain = -4dB
1 in ≥ 45 hours
1 in 32.0 hours
TBD
1 in 192.0 hours
1 in ≥ 10 hours
1 in 10.6 hours
TBD
1 in 19.9 hours
1 in ≥ 35 hours
1 in 39.8 hours
TBD
1 in 123.0 hours
Table 3 - Typical Off Hook Mode Talkoff Immunity Performance
Condition 1
Condition 2
Condition 3
SR-TSV-002476
Requirement
Test Result for 0 dB Near End
Speech Attenuation
Test Result for 8 dB Near End
Speech Attenuation
Vdd = 5V ± 10% (GS2 gain = 0dB) and 3V ± 10% (GS2 gain = -4dB)
≥ 99.5%
99.2%
99.9%
≥ 93.0%
79.6%
93.5%
≥ 99.5%
97.6%
99.7%
Table 4 -Typical Off Hook Mode Talkdown Immunity Performance
6
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