MT88E43B
Data Sheet
Item
BT
Bellcore
Low tone
frequency
2130Hz ±1.1%
2130Hz ±0.5%
High tone
frequency
2750Hz ± 1.1%
2750Hz ± 0.5%
Received
-2dBV to -40dBV
-14dBmb to
signal level
per tone on-hook1 - 32dBm per tone
(0.22dBm2 to
-37.78dBm)
off-hook
Signal reject
level
-46dBV
-45dBm
(-43.78dBm)
Signal level
differential
(twist)
up to 7dB
up to 6dB
Unwanted
signals
<= -20dB
<= -7dBm ASL3
near end speech
(300-3400Hz)
Duration
88ms to 110ms4
75ms to 85ms
Yes
Speech
present
No
Table 1 - Dual Tone Alert Signal Characteristics
1. In the future BT may specify the off-hook signal level as
-15 dBm to -34 dBm per tone for BT CIDCW.
2. The signal power is expressed in dBm referenced to 600 ohm
at the CPE A/B (tip/ring) interface.
3. ASL = active speech level expressed in dBm referenced to
600 ohm at the CPE tip/ring interface. The level is measured
according to method B of Recommendation P.56 "Objective
Measurement of Active Speech Level" published in the CCITT
Blue Book, volume V "Telephone Transmission Quality" 1989.
EPL (Equivalent Peak Level) = ASL+11.7 dB
4. SIN227 suggests that the recognition time should be not less
than 20 ms if both tones are detected.
Dual Tone Detection Guard Time
When the dual tone alert signal is detected by the MT88E43, ESt goes high. When the alerting signal ceases to be
detected, ESt goes low.
The ESt pin signals raw detection of CAS/Alerting Tones. Since both Bellcore and BT applications require a
minimum duration for valid signals, ESt detection must be guard time qualified. The StD pin provides guard time
qualified CAS/Alerting Tone detection. When the MT88E43 is used in a caller identity system, StD indicates correct
CAS/Alerting Tone detection.
Figure 4 shows the relationship between the St/GT, ESt and StD pins. It also shows the operation of a guard time
circuit.
The total recognition time is tREC = tGP + tDP, where tGP is the tone present guard time and tDP is the tone present
detect time (refer to timing between ESt, St/GT and StD in Figures 17 and 20).
The total tone absent time is tABS = tGA + tDA, where tGA is the tone absent guard time and tDA is the tone absent
detect time (refer to timing between ESt, St/GT and StD in Figures 17 and 20).
6
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