參數(shù)資料
型號(hào)： ADAV803
廠商： Analog Devices, Inc.
元件分類： Codec
英文描述： Audio Codec for Recordable DVD
中文描述： 音頻編解碼器可刻錄DVD
文件頁(yè)數(shù)： 20/56頁(yè)
文件大小： 906K
代理商： ADAV803
ADAV803
The worst-case images can be computed from the zero-order
hold frequency response:
Rev. 0 | Page 20 of 56
The
192 kHz:
s would appear for
f
S_IN
equal to
z = 125.1 dB
+
96 kHz = 125.1 dB
b
ro.
further reduction can be realize because only one interpolated
sample is ta
ken at the output at the f
S_OUT
rate, so only one
convolution needs to be performed per f
S_OUT
period instead of
2
20
convolutions. A 64-tap FIR filter for each f
S_OUT
sample is
sufficient to suppress the images caused by the interpolation.
the
of
riod with a clock
-
mber of coefficients in ROM, the SRC
r
y
tput
nd the length of the
convolution is increased by a factor of (f
S_IN
/f
S_OUT
).
This technique is supported by the Fourier transform property
that, if f(t) is F(ω), then f(k × t) is F(ω/k). Thus, the range of
decimation is limited by the size of the RAM.
SRC Architecture
The architecture of the sample rate converter is shown in
Figure 32. The sample rate converter’s FIFO block adjusts the
left and right input samples and stores them for the FIR filter’s
convolution cycle. The f
S_IN
counter provides the write address
to the FIFO block and the ramp input to the digital servo loop.
The ROM stores the coefficients for the FIR filter convolution
and performs a high order interpolation between the stored
coefficients. The sample rate ratio block measures the sample
rate for dynamically altering the ROM coefficients and scaling
o
servo loop auto ati
m
cally tracks the f
and provides the RAM and ROM start addresses for the s
the FIR filter convolution.
S_IN
S_OUT
sample rates
tart of
maximum image
= sin (×
F
/
f
S_INTERP
)/(×
F
/
f
S_INTERP
)
where:
F
is the frequency of the worst-case image that would be
2
20
×
f
S_IN
±
f
S_IN
/2.
f
S_INTERP
is
f
S_IN
× 2
20
.
following worst-case image
Image at f
S_INTERP
96 kH
Image at f
S_INTERP
Hardware Model
The output rate of the low-pass filter in Figure 30 is the
interpolation rate:
2
20
× 192,000 kHz = 201.3 GHz
Sampling at a rate of 201.3 GHz is clearly impractical, not to
mention the number of taps required to calculate each
interpolated sample. However, because interpolation by 2
20
involves zero-stuffing 2
20
1 samples between each f
S_IN
sample,
most of the multiplies in the low-pass FIR filter are y ze
A
d,
One difficulty with the above approach is that the correct
interpolated sample must be selected upon the arrival of f
S_OUT
.
Because there are 2
20
possible convolutions per f
S_OUT
period,
arrival of the f
S_OUT
clock must be measured with an accuracy
1/201.3 GHz = 4.96 ps. Measuring the f
S_OUT
pe
of 201.3 GHz frequency is clearly impossible; instead, several
coarse measurements of the f
S_OUT
clock period are made and
averaged over time.
Another difficulty with the above approach is the number of
coefficients required. Because there are 2
20
possible convolu-
tions with a 64-tap FIR filter, there must be 2
20
polyphase
coefficients for each tap, which requires a total of 2
26
coeffi
cients. To reduce the nu
stores a small subset of coefficients and performs a high order
interpolation between the stored coefficients.
The above approach works when f
S_OUT
> f
S_IN
. However, when
the output sample rate, f
S_OUT
, is less than the input sample rate,
f
S_IN
, the ROM starting address, input data, and length of the
convolution must be scaled. As the input sample rate rises ove
the output sample rate, the antialiasing filter’s cutoff frequenc
must be lowered, because the Nyquist frequency of the ou
samples is less than the Nyquist frequency of the input samples.
To move the cutoff frequency of the antialiasing filter, the
coefficients are dynamically altered a
f the FIR filter length as well as the input data. The digital
and f
0
RIGHT DATA IN
LEFT DATA IN
FIFO
DIGITAL
SERVO LOOP
f
S_IN
COUNTER
ROM A
ROM B
ROM C
ROM D
SAMPLE RATE RATIO
HIGH
ORDER
INTERP
FIR FILTER
L/R DATA OUT
f
S_IN
f
S_OUT
SAMPLE
RATE RATIO
EXTERNAL
RATIO
Figure 32. Architecture of the Sample Rate Converter
The FIFO receives the left and right input data and adjusts the
amplitude of the data for both the soft muting of the sample
rate converter and the scaling of the input data by the sample
rate ratio before storing the samples in the RAM. The input data
is scaled by the sample rate ratio, because, as the FIR filter
length of the convolution increases, so does the amplitude of the
convolution output. To keep the output of the FIR filter from
saturating, the input data is scaled down by multiplying it by
(f
S_OUT
/f
S_IN
) when f
S_OUT
< f
S_IN
. The FIFO also scales the input
data for muting and unmuting of the SRC.
The RAM in the FIFO is 512 words deep for both left and right
channels. An offset to the write address provided by the f
S_IN
counter is added to prevent the RAM read pointer from
overlapping the write address. The minimum offset on the SRC
is 16 samples. However, the group delay and mute-in register
can be used to increase this offset.
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ADAV803AST 制造商:Analog Devices 功能描述:AUDIO CODEC FOR RECORDABLE DVD - Bulk
ADAV803ASTZ 功能描述:IC CODEC AUDIO R-DVD 3.3V 64LQFP RoHS:是 類別:集成電路 (IC) >> 接口 - 編解碼器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:立體聲音頻 數(shù)據(jù)接口:串行 分辨率（位）:18 b ADC / DAC 數(shù)量:2 / 2 三角積分調(diào)變:是 S/N 比，標(biāo)準(zhǔn) ADC / DAC (db):81.5 / 88 動(dòng)態(tài)范圍，標(biāo)準(zhǔn) ADC / DAC (db):82 / 87.5 電壓 - 電源，模擬:2.6 V ~ 3.3 V 電壓 - 電源，數(shù)字:1.7 V ~ 3.3 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:48-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:48-TQFN-EP（7x7） 包裝:帶卷 (TR)
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ADAV804AST 制造商:Analog Devices 功能描述:AUDIO CODEC FOR RECORDABLE DVD - Bulk
ADAV804ASTZ 制造商:Analog Devices 功能描述:
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