SC88E43S 查看數據表（PDF） - Unspecified
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SC88E43S Datasheet PDF : 25 Pages
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Silan
Semiconductors
SC88E43
3.Ring Detection
In Bellcore’s CND/CNAM scheme, the CID FSK data is transmitted between the first and second ringing cycles.
The circuit in Figure 3 will generate a ring envelope signal (active low) at TRIGout for a ring voltage of at least
40Vrms. R5 and C3 filter the ring signal to provide an envelope output.
The diode bridge shown in Figure 3 works for both single ended and balanced ringing. A fraction of the ring
voltage is applied to the TRIGin input. When the voltage at TRIGin is above the Schmitt trigger high going
threshold VT+ , TRIGRC is pulled low as C3 discharges. TRIGout stays low as long as the C3 voltage stays below
the minimum VT+ .
In a CPE designed for CND/CNAM, the TRIGout high to low transition may be used to interrupt or wake up the
microcontroller. The controller can thus be put into power down mode to conserve power.
If precise ring duration determination is critical, capacitor C3 in Figure 3 may be removed. The microcontroller
will now be able to time the ring duration directly. The result will be that TRIGout will be low only as long as the
ringing signal is present.Previously the RC time constant would cause only one interrupt.
Dual Tone Alert Signal Detection
The BT on hook (idle state) caller ID scheme uses a dual tone alert signal whose characteristics are shown in
Table 1.
Bellcore specifications for a similar dual tone signal called CPE Alerting Signal (CAS) for use in off-hook data
transmission. For the CIDCW service, the CAS must be detected in the presence of near end speech. The CAS
detector must also be immune to imitation from near and farend speech.
Item
BT
Bellcore
Low tone frequency
2130Hz ± 1.1%
2130Hz ± 0.5%
High tone frequency
Received signal level
2750Hz ± 1.1%
-2dBV to –40dBV per tone on-
hook a (0.22dBm b to –37.78dBm)
2750Hz ± 0.5%
-14dBm b to –32dBm per tone
on-hook
Signal reject level
-46dBV (-43.78dBm)
-45dBm
Signal level differntial (twist)
Unwanted signals
Duration
Up to 7dB
≤-20dB(300-3400Hz)
88ms to 110ms d
Up to 6dB
≤–7dBm ASL c near end
speech
75ms to 85ms
Speech present
No
Yes
Table 1 Dual Tone Alert Signal Characteristics
a. In the future BT may specify the off-hook signal level as –15dBm to –34dBm per tone for BT CIDcw.
b. The signal power is expressed in dBm referenced to 600 ohm at the CPE A/B (tip/ring) interface.
c. 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+11.7dB.
d. SIN227 suggests that the recognition time should be not less than 20ms if both tones are detected.
HANGZHOU SILAN MICROELECTRONICS JOINT-STOCK CO.,LTD
Rev: 1.0 2000.12.31
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