Delta-Sigma A/D converters have become
widely accepted by data acquisition designers
because of their high performance. One of the
highest dynamic range Delta-Sigma converters is
the Crystal Semiconductor CS5321/CS5322 chip
set. The CS5321 is a fourth order modulator.
The CS5322 is a linear phase FIR decimation
filter. The purpose of this Technical Brief is to
compare the architecture of a general purpose
DSP chip with that of the CS5322.
General purpose DSPs are available which
support either fixed-point arithmetic or
floating-point arithmetic. Fixed-point processors
are lower cost but floating-point processors have
more horsepower. Fixed point processors work
with either 16, 20, or 24-bit data words, while
floating-point processors operate with 32-bit data
words. The size of the data word greatly
influences the cost of the chip and the cost of the
overall system. This is because data word length
determines the size of the registers used in the
processor, the number of pins required on the
package, and the word-width of the external
memory. If low cost is the number one goal in a
DSP design, the designer will specify a DSP
which has the smallest word size that the
application can tolerate.
JUL ’96
AN53REV2
1
Crystal Semiconductor Corporation
P.O. Box 17847, Austin, TX 78760
(512) 445 7222 FAX 445 7581
http://www.crystal.com
The CS5322 Digital Filter
by Jerome Johnston
Copyright  Crystal Semiconductor Corporation 1996
(All Rights Reserved)
AN53
Modulator Bitstream
Multiplier/
Accumulator
224 Word
24-bit RAM
24 x 24
Multiplier
256 Kbit
11 Bits ROM
33 11-bit
Coefficients
24 bits
50 Bits 48 Bits
50-bit Accumulator Array
(9 50-bit accumulators)
24-bit Serial Port
ROM
96 60-bit
Coefficients
24 bits
24 bits
60 bits
1
2
3
11-bit
24-bit
24-bit
8
4,8,16,32,64,... 256
2
FIR Coefficients Decimation
33
13
101
Figure 1. Digital Filter Block Diagram