MT8841AS datasheet(3/10 Pages) MITEL

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MT8841

5-13

Functional Description

The MT8841 Calling Number Identification Circuit

(CNIC) is a device compatible with the Bellcore

proposal (TR-NWT-000030) on generic requirements

for transmitting asynchronous voiceband data to

Customer Premises Equipment (CPE) from a serving

Stored

Program

Controlled

Switching

System

(SPCS)

Central

Office

(CO).

This

data

transmission technique is applicable in a variety of

services like Calling Number Delivery (CND), Calling

Name Delivery (CNAM) or Calling Identity Delivery

on Call Waiting (CIDCW) as specified in Custom

Local Area Signalling Service (CLASSSM) calling

information delivery features by Bellcore.

With CND, CNAM and CIDCW service, the called

subscriber has the capability to display or to store

the information on the calling party which is sent by

the CO and received by the CNIC.

In the CND service, information about a calling party

is embedded in the silent interval between the first

and second ring. During this period, the CNIC

receives and demodulates the 1200 baud FSK signal

(compatible with Bell-202 specification) and outputs

data into a 3-wire serial interface.

In the CIDCW service, information about a second

calling party is sent to the subscriber, while they are

engaged in another call. During this period, the CNIC

receives and demodulates the FSK signal as in the

CND case.

The

CNIC

designed

provide

the

data

transmission interface required for the above service

Figure 3 - Differential Input Configuration

IN+

IN-

VRef

MT8841

DIFFERENTIAL INPUT AMPLIFIER

C1 = C2 = 10 nF

R1 = R4 = R5 = 100 k

Ω

R2 = 60k

Ω, R3 = 37.5 kΩ

R3 = (R2R5) / (R2 + R5)

VOLTAGE GAIN

(AVdiff) = R5/R1

INPUT IMPEDANCE

(ZINdiff) = 2

2 + (1/

ωC)2

Figure 4 - Single-Ended Input Configuration

at the called subscriber location either in the on-hook

case as in CND, or the off-hook case, as in

CIDCW.

The functional block diagram of the CNIC

is shown in Figure 1. Note however, for CIDCW

applications, a separate CAS (CPE Alerting Signal)

detector is required.

In Europe, Caller ID and CIDCW services are being

proposed. These schemes may be different from

their North American counterparts. In most cases,

1200 baud CCITT V.23 FSK is used instead of Bell

202. Because the CNIC can also demodulate 1200

baud CCITT V.23 with the same performance, it is

suitable for these applications.

Although the main application of the CNIC is to

support CND and CIDCW service, it may also be

used in any application where 1200 baud Bell 202

and/or CCITT V.23 FSK data reception is required.

Input Configuration

The input arrangement of the MT8841 provides an

operational amplifier, as well as a bias source (VRef)

which is used to bias the inputs at VDD/2. Provision is

made for connection of a feedback resistor to the op-

amp output (GS) for adjustment of gain. In a single-

ended configuration, the input pins are connected as

shown in Figure 4.

Figure 3 shows the necessary connections for a

differential input configuration.

User Interface

The CNIC provides a powerful 3-pin interface which

can reduce the external hardware and software

requirements. The CNIC receives the FSK signal,

demodulates it, and outputs the extracted data to the

DATA pin. For each received stop bit start bit

sequence, the CNIC outputs a fixed frequency clock

string of 8 pulses at the DCLK pin. Each clock rising

RIN

IN+

IN-

VRef

MT8841

VOLTAGE GAIN

(AV) = RF / RIN

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