Data Conversion Circuits – D/A and A/D Converters
511
comparator
(1-bit ADC)
1-bit DAC
Kfs
(Clock)
+V REF
Integrator
S
V IN
+
_
+
_
To Digital filter
and Decimator
1-bit Data stream
-V REF
Figure 12.39 Block schematic representation of a delta modulator.
+Max
Quantized output from
Sigma-Delta Modulator
-Max
l
a
n
g
i
s
t
u
p
n
I H
/
S
m
o
r
f
0
Figure 12.40 Generation of a one-bit data stream.
intervals of time, in which case the counter output would represent the digital equivalent of the analogue
signal over those time intervals. Practical sigma-delta A/D converters use a digital decimation filter at
the output of the delta modulator to process the one-bit data stream to produce an output in the desired
format.
Sigma-delta A/D converters are widely used for contemporary voice-band, audio and high-resolution
precision industrial measurement applications. Their highly digital architecture is ideally suited for
such applications as it allows easy addition of digital functionality without significantly increasing
the cost. AD 1871 from Analog Devices is one such high-performance A/D converter of sigma-delta
architecture intended for digital audio applications.