SAA7712 Philips Semiconductors, SAA7712 Datasheet - Page 11

• Manufacturer Part Number: SAA7712
• Description: Sound effects DSP
• Manufacturer: Philips Semiconductors

Philips Semiconductors
8
8.1
8.1.1
Depending on the configuration of the equalizer sections,
the SAA7712H has 2 or 4 analog outputs which are
supplied by the same power supply. Each of these outputs
has a voltage and a current pin (see Fig.3). The signals are
available on 2 outputs (OUT0 and OUT1), or 4 outputs
(OUT0, OUT1, OUT2 and OUT3).
8.1.2
The sample rate (f
rate of the DSP. The word clock for the upsample filter and
the clock for the DACs, at 4f
the word select of the selected audio source.
1999 Aug 05
handbook, halfpage
Sound effects DSP
FUNCTIONAL DESCRIPTION
Analog outputs
BIT 0 to 13
A
DAC
NALOG OUTPUT CIRCUIT
FREQUENCY
Fig.3 Analog output circuit.
s
) of the selected source is the frame
MSB
DAC
MGS208
V ref
s
, are derived internally from
(OUT1_I)
(OUT1_V)
OUT0_I
OUT0_V
11
8.1.3
Each of the four low noise high dynamic range DACs
consists of a signed-magnitude DAC with current output,
followed by a buffer operational amplifier.
8.1.4
To reduce spectral components above the audio band, a
fixed 4 times oversampling and interpolating digital filter is
used. The filters give an out-of-audio-band attenuation of
at least 29 dB. The filter is followed by a first-order noise
shaper to expand the dynamic range to more than 105 dB.
The band around multiples of the sample frequency of the
DAC (4f
must be added in parallel with the DAC output amplifier to
attenuate this out-of-band noise further to an acceptable
level.
In Fig.4 the overall frequency spectrum at the DAC audio
output without external capacitor or low-pass filter for the
audio sampling frequencies of 38 kHz is shown. In Fig.5
the detailed spectrum around f
38, 44.1 and 48 kHz. The pass band bandwidth ( 3 dB) is
1
2
f
s
.
s
) is not affected by the digital filter. A capacitor
DAC
U
PSAMPLE FILTER
S
s
is shown for an f
Preliminary specification
SAA7712H
s
of