MT88E46
Advance Information
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.
The MT88E46 offers an optimal solution which
combines Bellcore compliant speech immunity and
MEI compatibility. Two input op-amps allow the
MT88E46 to be connected to both Tip/Ring and to
the receive pair of the telephone hybrid or speech IC
(the 4-wire side). Each connection can be differential
or single ended. FSK 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
Test Result for
0dB Near End
Speech
Attenuation using
Pre-emphasized
Speech only
SR-TSV-002476
Requirement
Test Result for 0dB Near
End Speech Attenuation
using Pre-emphasized
Speech for Near End,
Normal Speech for Far
End
Test Result for 6dB Near
End Speech Attenuation
using Pre-emphasized
Speech only
Vdd = 5V
±
10%, GS2 gain = 0dB
Condition 1
Condition 2
Condition 3
1 in
≥
45 hours
1 in
≥
10 hours
1 in
≥
35 hours
1 in
≥
45 hours
1 in
≥
10 hours
1 in
≥
35 hours
1 in
48.0
hours
1 in 8.6 hours
1 in
37.4
hours
1 in
96.0
hours
1 in
10.1
hours
1 in
43.0
hours
1 in
96.0
hours
1 in
16.5
hours
1 in
113.1
hours
Vdd = 3V
±
10%, GS2 gain = -4dB
Condition 1
Condition 2
Condition 3
1 in 32.0 hours
1 in
10.6
hours
1 in
39.8
hours
TBD
TBD
TBD
1 in
192.0
hours
1 in
19.9
hours
1 in
123.0
hours
Table 3. Typical Off Hook Mode Talkoff Immunity Performance
SR-TSV-002476
Requirement
Test Result for 0dB Near End
Speech Attenuation
Test Result for 8dB Near End
Speech Attenuation
Vdd = 5V
±
10% (GS2 gain = 0dB) and 3V
±
10% (GS2 gain = -4dB)
Condition 1
Condition 2
Condition 3
≥
99.5%
≥
93.0%
≥
99.5%
99.2%
79.6%
97.6%
99.9%
93.5%
99.7%
Table 4. Typical Off Hook Mode Talkdown Immunity Performance
6
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