cf8224c Nippon Precision Circuits Inc, (NPC), cf8224c Datasheet - Page 9

• Manufacturer Part Number: cf8224c
• Description: Dual-tone Receiver Ic
• Manufacturer: Nippon Precision Circuits Inc, (NPC)

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
Table 2. Function select
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.
Modulation type
Logic “1” data (mark)
Logic “0” data (space)
Signal level (mark)
Signal level (space)
Data transfer rate
HIGH
HIGH
LOW
LOW
LOW
S1
Parameter
HIGH
HIGH
LOW
LOW
LOW
S0
Continuous-phase binary frequency-shift-keying
1200 ± 12 Hz
2200 ± 22 Hz
−32 to −12 dBm
−36 to −12 dBm
1200 ± 12 baud
MODE
HIGH
LOW
LOW
LOW
LOW
Power-down
Dual-tone detection from DT1/DT2
FSK and dual-tone detection from
TIP/RING
FSK detection from TIP/RING
Test mode
Description
2
Function
SM8224C
1
HIGH
LOW (dual tone confirmation)
LOW (dual tone confirmation)
HIGH
STR
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