Introduction
1.4 Product Family
SEC ASIC
1-5
STD110
In a digital system the amplitude is quantized into discrete steps, and at the same
time the signal is sampled at discrete time intervals. This time interval is called
sampling time or sampling frequency. After sampling and quantization process,
the analog signal(A) becomes digital output (D).
Digital-to-Analog Converters
The D/A converters are the digital-to-analog conversion circuits, which are also
called DACs. They can be considered as decoding devices that accept digitally
coded signals and provide analog output in the form of currents or voltages. In
this manner, they provide an interface between the digital signal of the computer
systems and continuous signals of analog world. They are employed in a variety
ofapplications,fromCRTdisplaysystems andvoicesythesizerstoautomatictest
systems, digital controlled attenuators, and process control actuators. In addition,
they are key components inside most A/D converters.
Figure 1 shows the functional block diagram of a basic D/A converter system. The
input to the D/A converter is a digital word, made up a stream of binary bits
comprised of 1's and 0's. The output analog quantity A, which can be a voltage or
current, is related to the input as
1
2
1
where K is a scale factor, V
REF
is a reference voltage, n is the total number of bits,
and b1,b2,...,bn are the bit coefficients, which are quntized to be a 1 or a 0.
As a function of the input binary word which determines the bit coefficients, the
output exhibits
2
n
discrete voltage level ranging from zero to a maximum value of
with a minimum step change
Vo given as
\
Figure 1-1.
Functional Block Diagram of Basic D/A Converter
A
KV
REF
-----
2
2
2
-----
…
+
2
n
-----
+
+
=
Vo(max) V
REF
n
2
1
–
2
n
=
Vo
V
2
-------------
=
D/A
Converter
b1
b2
b3
bn
Analog Output
Digital
Data
Input
