UCB1510DB Просмотр технического описания (PDF) - Philips Electronics

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UCB1510DB

AC97 digital modem codec

Philips Electronics 

Philips Semiconductors

8.2 Analog interface

TOUTP

UCB1510

UCB1510

AC97 digital modem codec

1:1 transformer

A Rt

Rt

TINP

Rt

Rt

B

TINN

Rg

Ri

-

Rs

+

+

Rs

Ri

-

Rg

TOUTN

Fig 4. Typical telecom codec sidetone suppression circuit (without protection circuits).

9397 750 06856

Preliminary specification

An important built-in feature of the telecom codec is the sidetone suppression circuit.

The sidetone suppression circuit is activated when sidetone_enable of register 0x5A

is set.The sidetone suppression circuit subtracts part of the telecom output signal

from the telecom input signal. As a result the available dynamic range of the input

path can be more effectively utilized. If the sidetone suppression circuit is disabled,

the telecom input dynamic range can be largely occupied by the telecom output

signal.

The built-in side tone suppression circuit, shown in Figure 4, has a fixed subtraction

ratio, set be the resistors Rs and Ri, which equals 600⁄456. This ratio is calculated from

the following relations.

The impedance seen by the telephone line equals:

Zline

=

2

×





Rt

+

Rt

+

-RR---o-o---+×-----RR----ii

,

differential,

in

which

Rt

represents

winding

resistance

of the transformer, divided by 2. Assuming Ri >> Ro, then

Rline = Rt + Rt + Ro = 600 ⁄ 2 = 300Ω single ended.

A typical transformer has 156 Ω winding impedance, thus Ro should be 144 Ω. The

ratio of the telecom input and output voltage is, therefore:

V i(tel) = V o(tel) × 1---5---6--1---+5---6--3---+0---0--3--+-0---0-1---4---4-- = V o(tel) × 46----50---60-

Proper sidetone suppression thus requires Rs/Ri to be Vi/Vo.

Rev. 01 — 4 February 2000

© Philips Electronics N.V. 2000. All rights reserved.

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