參數(shù)資料
型號(hào)： TDA9852
廠商： NXP SEMICONDUCTORS
元件分類： 消費(fèi)家電
英文描述： I2C-bus controlled BTSC stereo/SAP decoder and audio processor
中文描述： SPECIALTY CONSUMER CIRCUIT, PDIP42
文件頁(yè)數(shù)： 9/40頁(yè)
文件大?。?/td> 258K
代理商： TDA9852
1997 Mar 11
9
Philips Semiconductors
Preliminary specification
I
2
C-bus controlled BTSC stereo/SAP
decoder and audio processor
TDA9852
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
μ
s fixed
de-emphasis circuit to the dematrix block.
I
NTEGRATED 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
S
ELECTOR
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 Tables 5 and 6 for
subaddress and Table 11 for data). 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
UTOMATIC 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
μ
F) at pin C
AV
determines the
attack and decay time constants. In addition the ratio of
attack and decay time can be changed via I
2
C-bus
(see Table 15). At power
on
, the discharged 4.7
μ
F
capacitor at C
AV
must be loaded by the internal decay
current. If AVL is chosen, this would result in an attenuated
AVL gain for about 10 seconds after power
on
. This can be
speeded up by choosing via I
2
C-bus an increased charge
current (about 10 times higher) for about the first
2 seconds after power
on
(see Table 6, CCD bit in
control 1 and Table 18).
E
FFECTS
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 I
2
C-bus;
see Table 10).
V
OLUME
/
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 I
2
C-bus
control (see Table 9). The left and right volume control
stages include two independent zero crossing detectors.
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 is realized between adjoining steps and
between any steps, but not from any step to mute. In this
case the GMU bit is needed to 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.
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