TDA9855WP Просмотр технического описания (PDF) - Philips Electronics

Номер в каталоге

Компоненты Описание

производитель

TDA9855WP

I2C-bus controlled BTSC stereo/SAP decoder and audio processor

Philips Electronics 

Philips Semiconductors

I2C-bus controlled BTSC stereo/SAP

decoder and audio processor

Product specification

TDA9855

dbx DECODER

The circuit includes all blocks required for the noise

reduction system in accordance with the BTSC system

specification. The output signal is fed through a 73 µs fixed

de-emphasis circuit to the dematrix block.

INTEGRATED FILTERS

The filter functions necessary for stereo and SAP

demodulation and part of the dbx filter circuits are provided

on-chip using transconductor circuits. The required filter

accuracy is attained by an automatic filter alignment

circuit.

Audio processor

SELECTOR

The selector allows selecting either the internal line out

signals LOR or LOL (dematrix output) or the external line

in signals LIR and LIL and combines the left and right

signals in several modes (see Table 12). The input signal

capability of the line inputs (LIR/LIL) is 2 V (RMS).

The output of the selector is AC-coupled to the automatic

volume level control circuit via pins SOR/SOL and

AVR/AVL to avoid offset voltages.

AUTOMATIC VOLUME LEVEL CONTROL

The automatic volume level stage controls its output

voltage to a constant level of typically 200 mV (RMS) from

an input voltage range of 0.1 to 1.1 V (RMS). The circuit

adjusts variations in modulation during broadcasting and

due to changes in the programme material. The function

can be switched off. To avoid audible ‘plops’ during the

permanent operation of the AVL circuit a soft blending

scheme has been applied between the different gain

stages. A capacitor (4.7 µF) at pin CAV determines the

attack and decay time constants. In addition the ratio of

attack and decay time can be changed via the I2C-bus

(see notes 7 and 8 of Chapter “Characteristics”).

EFFECTS

The audio processor section offers the following mode

selections: linear stereo, pseudo stereo, spatial stereo and

forced mono.The spatial mode provides an antiphase

crosstalk of 30% or 52% (switchable via the I2C-bus;

see Table 18).

VOLUME/LOUDNESS

The volume control range is from +16 dB to −71 dB in

steps of 1 dB and ends with a mute step (see Table 8).

Balance control is achieved by the independent volume

control of each channel. The volume control blocks

operate in combination with the loudness control. The filter

is linear when maximum gain for volume control is

selected. The filter characteristic changes automatically

over a range of 28 dB down to a setting of −12 dB.

At −12 dB volume control the maximum loudness boost is

obtained. The filter characteristic is determined by external

components. The proposed application provides a

maximum boost of 17 dB for bass and 4.5 dB for treble.

The loudness may be switched on or off via I2C-bus

control (see Table 14). The left and right volume control

stages include two independent zero-crossing detectors.

In the zero-crossing mode a change in volume is

automatically activated but not executed. The execution is

enabled at the next zero-crossing of the signal. If a new

volume step is activated before the previous one has been

processed, the previous value will be executed first, and

then the new value will be activated. If no zero-crossing

occurs the next volume transmission will enforce the last

activated volume setting.

The zero-crossing mode is realized between adjoining

steps and between any steps, but not from any step to

mute. In this case the GMU bit is required for use. In case

only one channel has to be muted, two steps are

necessary. The first step is a transmission of any step to

−71 dB and the second step is the −71 dB step to mute

mode. The step of −71 dB to mute mode has no

zero-crossing but this is not relevant. This procedure has

to be provided by software.

BASS CONTROL

A single external 33 nF capacitor for each channel in

combination with a linear operational amplifier and internal

resistors provides a bass control range of +16.5 to −12 dB

in steps of 1.5 dB at low frequencies (40 Hz). Internally the

basic step width is 3 dB, with intermediate steps obtained

by a toggle function that provides an additional 1.5 dB

boost or attenuation (see Table 9). It should be noted that

both loudness and bass control together result in a

maximum bass boost of 34.5 dB for low volume steps.

TREBLE CONTROL

The adjustable range of the treble control stage is from

−12 to +12 dB in steps of 3 dB. The filter characteristic is

determined by an external 5.6 nF capacitor for each

channel. The logic circuitry is arranged in a way that the

same data words (06H to 16H) can be used for both tone

controls if a bass control range from −12 to +12 dB and a

treble control range from −12 to +12 dB with 3 dB steps

are used (see Tables 9 and 10).

1997 Nov 04

10

Share Link: