saa7825 NXP Semiconductors, saa7825 Datasheet - Page 18

• Manufacturer Part Number: saa7825
• Description: Cd Audio Decoder, Digital Servo And Filterless Dac With Integrated Pre-amp And Laser Control
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.9
7.9.1
When pre-emphasis is detected in the Q-channel
subcode, the digital filter automatically includes a
de-emphasis filter section. When de-emphasis is not
required, a phase compensation filter section controls the
phase of the digital oversampling filter to
band 0 to 16 kHz. With de-emphasis the filter is not phase
linear.
If the de-emphasis signal is set to be available at pin V5,
selected via decoder register D, then the de-emphasis
filter is bypassed.
7.9.2
For optimizing performance with an external DAC, the
SAA7825 contains a 2 to 4 times oversampling IIR filter.
The filter specification of the 4 times oversampling filter is
given in Table 5.
These attenuations do not include the sample-and-hold at
the external DAC output or the DAC post filter. When using
the oversampling filter, the output level is scaled 0.5 dB
down to avoid overflow on full-scale sine wave inputs
(0 to 20 kHz).
Table 5 Filter specification
2003 Aug 13
CD audio decoder, digital servo and filterless
DAC with integrated pre-amp and laser control
PASS BAND
19 to 20 kHz
0 to 9 kHz
Audio functions
D
D
E
IGITAL OVERSAMPLING FILTER
-
EMPHASIS AND PHASE LINEARITY
STOP BAND
24 to 27 kHz
27 to 35 kHz
35 to 64 kHz
64 to 68 kHz
69 to 88 kHz
24 kHz
68 kHz
ATTENUATION
1 within the
0.001 dB
0.03 dB
25 dB
38 dB
40 dB
50 dB
31 dB
35 dB
40 dB
18
7.9.3
A 1-sample linear interpolator becomes active if a single
sample is flagged as erroneous but cannot be corrected.
The erroneous sample is replaced by a level midway
between the preceding and following samples. Left and
right channels have independent interpolators. If more
than one consecutive non-correctable sample is found, the
last good sample is held. A 1-sample linear interpolation is
then performed before the next good sample; see Fig.12.
In CD-ROM modes (i.e. the external DAC interface is
selected to be in a CD-ROM format) concealment is not
executed.
7.9.4
A digital level controller is present on the SAA7825 which
performs the functions of soft mute, full-scale, attenuation
and fade; these are selected via decoder register 0:
7.9.5
The peak detector measures the highest audio level
(absolute value) on positive peaks for left and right
channels. The 8 most significant bits are output in the
Q-channel data in place of the CRC bits. Bits 81 to 88
contain the left peak value (bit 88 = MSB) and bits 89 to 96
contain the right peak value (bit 96 = MSB). The values
are reset after reading Q-channel data via pin SDA.
Mute: signal reduced to 0 in a maximum of 128 steps;
3/n ms
Attenuation: signal scaled by 12 dB
Full-scale: ramp signal back to 0 dB level; from mute it
takes 3/n ms
Fade: activates a 128 stage counter which allows the
signal to be scaled up or down in 0.07 dB steps
– 128 = full-scale
– 120 = 0.5 dB (i.e. full-scale if oversampling filter is
– 32 = 12 dB
– 0 = mute.
used)
C
M
P
EAK DETECTOR
ONCEALMENT
UTE
,
FULL
-
SCALE
,
ATTENUATION AND FADE
Objective specification
SAA7825