TDA9855WP Philips Semiconductors, TDA9855WP Datasheet - Page 10

• Manufacturer Part Number: TDA9855WP
• Description: I2C-bus controlled BTSC stereo/SAP decoder and audio processor
• Manufacturer: Philips Semiconductors

Philips Semiconductors
dbx
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 s fixed
de-emphasis circuit to the dematrix block.
I
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
S
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.
A
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 F) at pin C
attack and decay time constants. In addition the ratio of
attack and decay time can be changed via the I
(see notes 7 and 8 of Chapter “Characteristics”).
E
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 I
see Table 18).
V
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
1997 Nov 04
NTEGRATED FILTERS
ELECTOR
UTOMATIC VOLUME LEVEL CONTROL
FFECTS
OLUME
I
decoder and audio processor
2
DECODER
C-bus controlled BTSC stereo/SAP
/
LOUDNESS
AV
determines the
2
C-bus;
2
C-bus
10
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 I
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
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.
B
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.
T
The adjustable range of the treble control stage is from
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).
71 dB and the second step is the 71 dB step to mute
12 to +12 dB in steps of 3 dB. The filter characteristic is
REBLE CONTROL
ASS CONTROL
Product specification
TDA9855
2
C-bus