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PDF TEA0679 Data sheet ( Hoja de datos )
| Número de pieza | TEA0679 | |
| Descripción | I2C-bus controlled dual Dolby* B-type noise reduction circuit for playback applications | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TEA0679T
I2C-bus controlled dual Dolby*
B-type noise reduction circuit for
playback applications
Product specification
Supersedes data of 1998 Jun 24
File under Integrated Circuits, IC01
1998 Nov 12
1 page  
Philips Semiconductors
I2C-bus controlled dual Dolby* B-type noise
reduction circuit for playback applications
Product specification
TEA0679T
FUNCTIONAL DESCRIPTION
The following functions can be controlled via the I2C-bus:
• Equalization time constant switching
• Head switching
• Automatic Music Search (AMS) modes and blank skip
• Noise Reduction (NR) on/off switching
• Mute switching
• Equalization amplifier gain adjustment
• Output offset adjustment.
Dolby B noise reduction only operates correctly if the 0 dB
Dolby level is adjusted at 387.5 mV. The gain adjustment
can also be used to change the AMS level detector
threshold. The IC is able to generate an internal power-on
reset to guarantee a proper start-up behaviour.
Two of the above functions can be controlled via separate
pins (optional), if required.
Head switching is achieved when pin HS is connected to a
LOW level (input IN2 active) or connected to a HIGH level
(input IN1 active).
Equalization time constant switching (70 or 120 µs) is
achieved when pin EQS is connected to a LOW level
(70 µs) or connected to a HIGH level (120 µs).
If I2C-bus control is used the respective external function
control pin has to be left open-circuit. When open-circuit
the current state of the function can be observed at these
pins.
Automatic Music Search (AMS) modes and blank skip
If AMS is active (search mode bits SMOD1 = 1 and
SMOD0 = 0 or 1) the NR function is internally switched off
and the equalization time constant is internally forced to
70 µs. The signals of both channels are full-wave rectified
and then added. This means that even if one channel
appears inverted to the other channel the normal AMS
function is ensured.
It is possible to choose between the AMS scan and the
AMS latch mode via the I2C-bus. Due to the usage of an
internal flip-flop the switching from one mode to the other
must be done via the AMS off state. This guarantees an
appropriate flip-flop reset:
• Start from the initial AMS off state (SMOD1 = 0 and
SMOD0 = 0 or 1)
• Enable the desired AMS operation mode: AMS latch
mode (SMOD1 = 1 and SMOD0 = 0) or AMS scan mode
(SMOD1 = 1 and SMOD0 = 1).
For further information on music search see Figs 4 to 8.
If blank skip is active (SMOD1 = 0 and SMOD0 = 1)
periods of music can be detected in the playback mode
using the AMS pin as the detector output. It is possible to
defeat this function via the I2C-bus (SMOD1 = 0 and
SMOD0 = 0). For further information on blank skip
see Figs 9 and 10.
Offset adjustment procedure
The offset adjustment is performed using two bits in the
I2C-bus write byte 0. The offset monitor bit OMOR enables
the AMS output to indicate whether the selected offset
value is positive or negative. The channel select bit OFCH
selects the channel (A or B) which is currently monitored
by the output at pin AMS. The monitoring needs a few
microseconds until the output result is valid. A complete
offset adjustment is performed in the following way:
• Adjust the output to Dolby level using the I2C-bus
controlled equalization gain adjustment
• Enable the offset monitor and select the channel to be
monitored by transmitting the bits OMOR = 1 and OFCH
(0 = Channel A, 1 = Channel B) to the IC
• If the monitor output (pin AMS) is LOW send the next
offset value OFFCHA or OFFCHB one offset step below
the last valid value. If the monitor output (pin AMS) is
HIGH send the next offset value OFFCHA or OFFCHB
one offset step above the last valid value
• Repeat the last two steps until the monitor output
changes its polarity
• If necessary store the transmitted digital offset value for
the selected channel.
The start value is either set by the power-on reset or the
last I2C-bus transmission. The offset adjustment can be
performed during the power-on reset condition and also
each time the tape driver is not active. A complete digital
offset data set consists of four values: one for each head
(head 1 and head 2) in each channel. After an offset value
transmission the IC stores one value for channel A and
one value for channel B. If a head switch is performed
these values have to be updated via the I2C-bus for the
alternative head.
1998 Nov 12
5
5 Page 
Philips Semiconductors
I2C-bus controlled dual Dolby* B-type noise
reduction circuit for playback applications
Product specification
TEA0679T
Short description of music search
A system for music search consists mainly of a level and a
time detection circuit (see Fig.4). For adapting and
decoupling the input signal is amplified (A), then rectified
(B) and smoothed with a time constant (C). Thus the
voltage at (C) corresponds to the signal level and will be
compared to the predefined pause level at the first
comparator (D), the level detector. If the signal level
becomes smaller than the pause level, the level detector
changes its output signal. Due to the output level of the
level detector the capacitor of the second time constant (E)
will be charged, respectively discharged.
If the pause level of the input signal remains for a certain
time period, the voltage at the capacitor reaches a certain
value, which corresponds to an equivalent time value.
The voltage at the capacitor will be compared to a
predefined time-equivalent voltage by the second
comparator (F), the time detector. If the pause level of the
input signal remains for this predefined time, the time
detector changes its output level to pause found status.
handbook, full pagewidth
(A)
INPUT
(B) (C)
(D) (E)
(F)
COMPARATOR 1
t1 VI
COMPARATOR 2
t2 Vt
OUTPUT
AMPLIFIER RECTIFIER
LEVEL DETECTOR
TIME DETECTOR
MED624
Fig.4 Integrated music search function.
1998 Nov 12
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet TEA0679.PDF ] | |
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