CF8224C Просмотр технического описания (PDF) - Nippon Precision Circuits
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CF8224C Datasheet PDF : 11 Pages
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SM8224C
FUNCTIONAL DESCRIPTION
The SM8224C receiver with caller ID service conforms to the Bellcore standards. It incorporates FSK demod-
ulator and dual-tone detection functions in a single chip. It has a dedicated dual-tone signal input so that the
FSK signal input amplification and dual-tone signal input amplification can be set independently. This allows
systems can be easily constructed that provide pre- and mid-conversation information services.
FSK Demodulator
Calling number identification service is sent as an FSK signal, and the SM8224C FSK demodulator processes
this signal. The FSK signal conforms to the following Bellcore standard.
Table 1. FSK signal
Parameter
Modulation type
Logic “1” data (mark)
Logic “0” data (space)
Signal level (mark)
Signal level (space)
Data transfer rate
Description
Continuous-phase binary frequency-shift-keying
1200 ± 12 Hz
2200 ± 22 Hz
−32 to −12 dBm
−36 to −12 dBm
1200 ± 12 baud
Table 2. Function select
S1
S0
MODE
Function
STR
LOW
LOW
HIGH Power-down
HIGH
HIGH
LOW
LOW Dual-tone detection from DT1/DT21
LOW (dual tone confirmation)
LOW
HIGH
LOW
FSK and dual-tone detection from
TIP/RING
LOW (dual tone confirmation)
HIGH
LOW
HIGH
LOW
LOW FSK detection from TIP/RING
LOW Test mode2
HIGH
1. DT1, DT2, DTQ are active in this mode only.
2. Test mode should not be used.
Note: S1, S0, MODE setting should be used from above combination except Test mode.
Dual Tone Detector
When using mid-conversation information services, 2 mixed signals of 2130Hz and 2750Hz are sent on lines
L1 and L2. The SM8224C detects the 2 signals from the background noise. It uses 2 separate high-order filters
with center frequencies of 2130Hz and 2750Hz to detect the presence of the signal frequencies.
In series with the filters are level detectors. When the input level exceeds the preset rating, the signal is
detected. When the input level is below the rating, the signal is not detected.
If both the 2130Hz and 2750Hz signals are simultaneously detected, DTDET goes HIGH and starts charging
the time constant circuit comprised by an external capacitor and external resistor. When the time constant cir-
cuit voltage rises above a fixed voltage level, STR signal goes LOW to indicate dual tone detection.
SEIKO NPC CORPORATION —9
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