Digital Signal Processing Reference
In-Depth Information
Figure 5.1
Quantizers illustrated by schemes (a) and (b) are randomized and the pseudo-
randomized quantizer is illustrated by scheme (c)
respectively. Pseudo-random number generators (PRNGs) with digital-to-analog
converters (DACs) added are typically used for generation of the analog auxiliary
pseudo-random processes needed for that. At first glance all three quantizers
shown in Figure 5.1 look equivalent. However, there are significant differences
between the first two schemes and the third, shown in Figure 5.1(c). While both
of the first two schemes depict a randomized quantizer, the third diagram is a
scheme of a pseudo-randomized quantizer.
In all of the illustrated cases the quantizing operation is based on comparing
signal instantaneous values with variable thresholds generated by a PRNG to-
gether with a DAC. When the quantizing operation is performed in this way, the
positions of the threshold levels at all
are in fact known. Whether this infor-
mation is used or not is another question, but it is there, given at each
t
k
even in the
digital form. Evidently, this information is not used at randomized quantization
when the quantized signal is simply defined as
n
k
q
.
t
k
{
}
