參數(shù)資料
型號(hào): EVAL-ADAV801EBZ
廠商: Analog Devices Inc
文件頁數(shù): 10/60頁
文件大小: 0K
描述: BOARD EVALUATION FOR ADAV801
標(biāo)準(zhǔn)包裝: 1
主要目的: 接口,模擬前端(AFE)
已用 IC / 零件: ADAV801
已供物品:
相關(guān)產(chǎn)品: ADAV801ASTZ-ND - IC CODEC AUDIO R-DVD 3.3V 64LQFP
ADAV801ASTZ-REEL-ND - IC CODEC AUDIO R-DVD 3.3V 64LQFP
ADAV801
Rev. A | Page 18 of 60
DAC SECTION
The ADAV801 has two DAC channels arranged as a stereo pair
with single-ended analog outputs. Each channel has its own
independently programmable attenuator, adjustable in 128 steps
of 0.375 dB per step. The DAC can receive data from the
playback or auxiliary input ports, the SRC, the ADC, or the
DIR. Each analog output pin sits at a dc level of VREF, and
swings 1.0 V rms for a 0 dB digital input signal. A single op amp
third-order external low-pass filter is recommended to remove
high frequency noise present on the output pins. Note that the
use of op amps with low slew rate or low bandwidth can cause
high frequency noise and tones to fold down into the audio
band. Care should be taken in selecting these components.
The FILTD and VREF pins should be bypassed by external
capacitors to AGND. The FILTD pin is used to reduce the noise
of the internal DAC bias circuitry, thereby reducing the DAC
output noise. The voltage at the VREF pin can be used to bias
external op amps used to filter the output signals. For
applications in which the VREF is required to drive external
op amps, which might draw more than 50 μA or have dynamic
load changes, extra buffering should be used to preserve the
quality of the ADAV801 reference.
The digital input data source for the DAC can be selected from
a number of available sources by programming the appropriate
bits in the datapath control register. Figure 27 shows how the
digital data source and the MCLK source for the DAC are
selected. Each DAC has an independent volume register giving
256 steps of control, with each step giving approximately
0.375 dB of attenuation. Note that the DACs are muted by
default to prevent unwanted pops, clicks, and other noises
from appearing on the outputs while the ADAV801 is being
configured. Each DAC also has a peak-level register that records
the peak value of the digital audio data. Reading the register
clears the peak.
Selecting a Sample Rate
Correct operation of the DAC is dependent upon the data rate
provided to the DAC, the master clock applied to the DAC, and
the selected interpolation rate. By default, the DAC assumes
that the MCLK rate is 256 times the sample rate, which requires
an 8× oversampling rate. This combination is suitable for
sample rates of up to 48 kHz.
For a 96 kHz data rate that has a 24.576 MHz MCLK (256 × fS)
associated with it, the DAC MCLK divider should be set to
divide the MCLK by 2. This prevents the DAC engine from
running too fast. To compensate for the reduced MCLK rate,
the interpolator should be selected to operate in 4 × (DAC
MCLK = 128 × fS). Similar combinations can be selected for
different sample rates.
04
57
7-
0
07
P
L
2I
N
T
E
R
NAL
P
L
1I
N
T
E
R
NAL
MC
LK
I
XI
N
REG 0x76
BITS[7:5]
REG 0x65
BITS[3:2]
REG 0x63
BITS[5:3]
DI
R
P
L
(
256
×
f S
)
DI
R
P
L
(
512
×
f S
)
DIR
PLAYBACK
AUXILIARY IN
ADC
MCLK
DIVIDER
DAC
MCLK
DAC
INPUT
Figure 27. Clock and Datapath Control on the DAC
MULTIBIT
Σ-Δ
MODULATOR
INTERPOLATOR
DAC
TO ZERO FLAG PINS
FROM DAC
DATAPATH
MULTIPLEXER
VOLUME/MUTE
CONTROL
PEAK
DETECTOR
ZERO DETECT
TO CONTROL
REGISTERS
ANALOG
OUTPUT
04
57
7-
00
8
Figure 28. DAC Block Diagram
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