SM8224B 데이터 시트보기 (PDF) - Nippon Precision Circuits

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SM8224B

Dual-Tone Receiver IC

Nippon Precision Circuits  

SM8224B

FUNCTIONAL DESCRIPTION

The SM8224B receiver with caller ID service con-

forms to the Bellcore standards. It incorporates FSK

demodulator 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-

FSK Demodulator

Calling number identification service is sent as an

FSK signal, and the SM8224B FSK demodulator

processes this signal.

The FSK signal conforms to the following Bellcore

standard.

tone signal input amplification can be set indepen-

dently. This allows systems can be easily constructed

that provide pre- and mid-conversation information

services.

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 −1 2 d B m

−36 to −1 2 d B m

1200 ± 12 baud

Table 2. Function select

S1

LOW

HIGH

LOW

HIGH

LOW

S0

LOW

LOW

HIGH

HIGH

LOW

MODE

HIGH

LOW

LOW

LOW

LOW

Function

Pow er-dow n

Dual-tone detection from DT1/DT21

FSK and dual-tone detection from TIP/RING

FSK detection from TIP/RING

Test mode2

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.

STR

HIGH

LOW (dual tone confirmation)

LOW (dual tone confirmation)

HIGH

Dual Tone Detector

When using mid-conversation information services,

2 mixed signals of 2130Hz and 2750Hz are sent on

lines L1 and L2. The SM8224B 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 frequen-

cies.

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 simulta-

neously detected, DTDET goes HIGH and starts

charging the time constant circuit comprised by an

external capacitor and external resistor. When the

time constant circuit voltage rises above a fixed volt-

age level, STR signal goes LOW to indicate dual

tone detection.

NIPPON PRECISION CIRCUITS—9

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