ADAV803 Analog Devices, ADAV803 Datasheet - Page 19

• Manufacturer Part Number: ADAV803
• Description: Audio Codec
• Manufacturer: Analog Devices

SAMPLE RATE CONVERTER (SRC) FUNCTIONAL O
During asynchronous samp
conv
The sim
conversi
samplers, as shown in Figure 29. In an asynchronous syste
is never equal to T1, nor is the ratio between T2 and T1 ra
As a result, samples
an error in the resam
The frequency domain shows the wide side lobes tha esult
from this error when the sampling of f
the attenu
orde
order h
T1 i
resampling at f
significantly reduced, however, through interpolation of t
input data at f
ADAV803 is concep
Conceptual High Interpolation Model
Interpolation of the input data by a factor of 2
(2
both the time domain and the frequency domain of
interpolation by a factor of 2
2
samples between each f
interpolated signal with a digital low-pass filter
images. In the time domain, it can be een
closest f
the nearest f
significantly reduces the resampling error.
20
FREQUENCY RESPONSE OF
WITH ZERO-ORDER HOLD SPECTRUM
20
involves the steps of zero-stuffing (2
Figure 29. Zero-Order Hold Used by f
s an irrational number, the error resulting f
− 1) samples between each f
IN
r hold. The images at f
erted at the same sample rate
old are i
S_IN
plest approach to an asynchronous sample rate
on is to use a zero-order hold between the two
f
S_IN
ated images from the SIN(x)/x nature of the zero-
× 2
S_IN
=1/T1
SPECTRUM OF ZERO-ORDER HOLD OUTPUT
S_IN
S_OUT
20
nfinite
sample in the case of no interpolation. This
sample from the zero-order hold, as opposed to
. Therefore, the sample rate converter in t
SPECTRUM OF
SIN(X)/X OF ZERO-ORDER HOLD
ca
at f
tually interpolated by a factor of 2
pling process.
n never be eliminated. The error can be
ly attenuated. Because t
ORIGINAL SIGNAL
SAMPLED AT
S_OUT
S_IN
f
ZERO-ORDER
f
S_OUT
S_OUT
S_IN
sample and convolving this
HOLD
le rate conversion, data can be
are repeated or dropped, producing
20
f
S_OUT
CONVOLVED
. Conceptually, interpolation b
(dc signal imag
S_IN
f
S_ OUT
S_IN
or at
SAMPLING
sample. Figure 30 shows
s
to Resample Data from f
S_OUT
20
differen
f
S_OUT
− 1) number of
th
is convolved with
at f
= 1/T2
he ratio of T2 to
es) of the zero-
20
rom the
t sam
to suppress the
involves placin
S_OUT
2 ×
OUT
ple
t r
selects the
f
20
S_OUT
.
rates.
he
m, T2
tional.
he
S_IN
y
Rev. 0 | Page 19 of 56
VERVIEW
g
In the frequency domain shown in Figure 31, the interpolation
expands the frequency axis
from the interpolation can be sufficiently attenuated by a good
low-pass filter. The images from the zero-order hold are now
pushed by a factor of 2
of the zero-order hold, which is f
zero-order hold are the determining factor for the fidelity of the
output at f
IN
IN
Figure 31. Frequency Domain of the Interpolation and Resamp
f
f
S_IN
S_IN
FREQUENCY DOMAIN OF SAMPLES AT
FREQUENCY DOMAIN OF THE INTERPOLATION
FREQUENCY DOMAIN OF
FREQUENCY DOMAIN
AFTER RESAMPLING
S_OUT
SIN(X)/X OF ZERO-ORDER HOLD
TIME DOMAIN OF
TIME DOMAIN OUTPUT OF THE LOW-PASS FILTER
TIME DOMAIN OF
TIME DOMAIN OF THE ZERO-ORDER HOLD OUTPUT
INTERPOLATE
INTERPOLATE
.
BY N
BY N
Figure 30. SRC Time Domain
20
closer to the infinite attenuation point
f
f
S_IN
S_OUT
of the zero-order hold. The images
LOW-PASS
f
LOW-PASS
S_OUT
FILTER
FILTER
SAMPLES
RESAMPLING
S_IN
RESAMPLING
× 2
2
f
S_IN
20
ZERO-ORDER
ZERO-ORDER
20
×
. The images at the
f
HOLD
HOLD
S_IN
2
2
20
f
20
S_IN
×
×
f
f
S_IN
S_IN
ADAV803
f
f
S_OUT
S_OUT
ling
OUT
OUT