CMX624 데이터 시트보기 (PDF) - MX-COM Inc

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CMX624

Bell 202 and V.23 Modem with Call Progress and DTMF

MX-COM Inc  

Bell 202 and V.23 Compatible Modem

15

CMX624 Preliminary Information

5 Application Notes

5.1 Line Interface

A line interface circuit is needed to provide DC isolation between the modem and the line, to perform line

impedance termination, and to set the correct transmit and receive signal levels.

5.1.1 4-Wire Line Interface

Figure 12 shows an interface circuit for use with a 600Ω 4-wire line. The line terminations are provided by

R10 and R15, while R11 and R13 should be selected to give the desired transmit and receive levels.

5.1.1.1 Receive Gain

The gain of the receive input amplifier (R12 / R11) should be set to compensate for the loss of the input

transformer and the supply voltage.

Assuming a transformer loss of about 1dB, R11 should be 91kΩ at VDD = 5.0V, or 130kΩ at 3.3V.

Rx

4-Wire

Line

Tx

RXAMPOUT

A

1:1

C10

R10

R12

R11

VBIAS

C11

RX-

RX+

TX

C13

R13

TXIN-

-

+

CMX624

R14

C12

1:1

R15

TX+

VBIAS

TX-

VBIAS

Figure 12: 4-Wire Line Interface Circuit

R10

600Ω ±1%

R15

600Ω ±1%

R11

See text ±1%

C10

100nF ±20%

R12

100kΩ ±1%

C11

220pF ±20%

R13

See text ±1%

C12

330pF ±20%

R14

100kΩ ±1%

C13

100nF ±20%

Tolerances for Resistors and Capacitors are as indicated unless otherwise stated.

Table 10: 4-Wire Line Interface Circuit components

Note: The relay circuit, AC and DC loads and line protection are not shown for clarity.

©1999 MX-COM, Inc.

www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480180.108

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

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