CMX624 Просмотр технического описания (PDF) - CML Microsystems Plc

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CMX624

V.23 / Bell 202 Modem

CML Microsystems Plc 

V23 / Bell 202 Modem

CMX624

1.6 Application Notes

1.6.1 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.

4-Wire Line Interface

Figure 8a 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.

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 transformer loss of about 1dB, R11 should be 91kΩ at 5.0V, or 130kΩ at 3.0V.

Note relay circuit, ac and dc loads and line protection not shown for clarity.

R10 600Ω

R11 See text

R12 100kΩ

R13 See text

R14 100kΩ

R15 600Ω

C10 100nF

C11 220pF

C12 330pF

C13 100nF

Resistors ±1%, capacitors ±20%.

Figure 8a 4-Wire Line Interface Circuit

 2003 CML Microsystems Plc

15

D/624/7

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