Theory of Operation
10-4 ADSP-21368 SHARC Processor Hardware Reference
Conceptual Model
In SRC theory, interpolation of the input data by a factor of 2
20
involves
placing (2
20
– 1) samples between each f
S_IN
sample. Figure 10-2 and
Figure 10-3 on page 10-6 shows both the time domain and the frequency
domain of interpolation by a factor of 2
20
. Conceptually, interpolation by
2
20
involves the steps of zero-stuffing (2
20
– 1) samples between each
f
S_IN
sample and convolving this interpolated signal with a digital
low-pass filter to suppress the images. In the time domain, it can be seen
that f
S_OUT
selects the closest f
S_IN
× 2
20
sample from the zero-order hold
as opposed to the nearest f
S_IN
sample in the case of no interpolation.
This significantly reduces the resampling error.
Figure 10-1. Zero-Order Hold Used by f
S_OUT
to Resample Data
From f
S_IN
ZERO-ORDER
HOLD
IN OUT
f
S_IN
=1/T1
f
S_OUT
=1/T2
ORIGINAL SIGNAL
SAMPLED AT f
S_IN
SIN(X)/X OF ZERO-ORDER HOLD
SPECTRUM OF ZERO-ORDER HOLD OUTPUT
SPECTRUM O F f
S_OUT
SAMPLING
f
S_OUT
2 × f
S_OUT
FREQUENCY RESPO NSE O F f
S_OUT
CONVO LVED WITH ZERO-ORDER
HOLD SP ECTRUM
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