SAA7824 Datasheet, PDF (19/89 Pages) NXP Semiconductors – CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control (PhonIC)

Philips Semiconductors
CD audio decoder, digital servo and filterless
DAC with integrated pre-amp and laser control
Product specification
SAA7824
7.9 Audio functions
7.9.1 DE-EMPHASIS AND PHASE LINEARITY
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 ≤ ±1° within the
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 DIGITAL OVERSAMPLING FILTER
For optimizing performance with an external DAC, the
SAA7824 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
PASS BAND
0 to 9 kHz
19 to 20 kHz
−
−
−
−
−
−
−
STOP BAND
−
−
24 kHz
24 to 27 kHz
27 to 35 kHz
35 to 64 kHz
64 to 68 kHz
68 kHz
69 to 88 kHz
ATTENUATION
≤0.001 dB
≤0.03 dB
≥25 dB
≥38 dB
≥40 dB
≥50 dB
≥31 dB
≥35 dB
≥40 dB
7.9.3 CONCEALMENT
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.13.
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 MUTE, FULL-SCALE, ATTENUATION AND FADE
A digital level controller is present on the SAA7824 which
performs the functions of soft mute, full-scale, attenuation
and fade; these are selected via decoder register 0:
• 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
used)
– 32 = −12 dB
– 0 = mute.
7.9.5 PEAK DETECTOR
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.
2003 Oct 01
19