4-16

Applications

RECEIVER SYSTEM FOR BRITISH TELECOM

SPEC POR 1151

The circuit shown in Fig. 9 illustrates the use of

MT8870D-1 device in a typical receiver system. BT

Spec defines the input signals less than -34 dBm as

the non-operate level.

This condition can be

to provide 3 dB attenuation, such that -34 dBm input

signal will correspond to -37 dBm at the gain setting

pin GS of MT8870D-1. As shown in the diagram, the

requirements when the total component tolerance is

6%. For better performance, it is recommended to

use the non-symmetric guard time circuit in Fig. 8.

Figure 8 - Non-Symmetric Guard Time Circuit

St/GT

ESt

Notes:

Figure 9 - Single-Ended Input Configuration for BT or CEPT Spec

IN+

IN-

GS

INH

PWDN

OSC 1

OSC 2

TOE

St/GT

ESt

StD

Q4

Q3

Q2

Q1

DTMF

Input

MT8870D-1

NOTES: