TEA0679 NXP Semiconductors, TEA0679 Datasheet - Page 5

• Manufacturer Part Number: TEA0679
• Description: I2c-bus Controlled dual Dolby* B-type Noise Reduction Circuit for Playback Applications
• Manufacturer: NXP Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The following functions can be controlled via the I
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 s) is
achieved when pin EQS is connected to a LOW level
(70 s) or connected to a HIGH level (120 s).
If I
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 s. 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 I
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:
1998 Nov 12
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.
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).
I
reduction circuit for playback applications
2
2
C-bus control is used the respective external function
C-bus controlled dual Dolby* B-type noise
2
C-bus. Due to the usage of an
2
C-bus:
5
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 I
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
I
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:
The start value is either set by the power-on reset or the
last I
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 I
alternative head.
2
C-bus write byte 0. The offset monitor bit OMOR enables
Adjust the output to Dolby level using the I
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.
2
C-bus transmission. The offset adjustment can be
2
C-bus (SMOD1 = 0 and
Product specification
TEA0679T
2
C-bus for the
2
C-bus