Data Conversion Circuits – D/A and A/D Converters
495
and the transfer function is given by
V out /V in = R 2 /R 1 1//1 + jR 2 R 4 CCD/R 3
(12.16)
It may be mentioned here that other types of digitally controlled filter are also possible using D/A
converters. One such possibility, for instance, is by using state variable techniques, which can be used
to design D/A converter based programmable filters to get low-pass, high-pass and band-pass functions
from the same circuit.
12.8 A/D Converters
After digital-to-analogue converters, the discussion in the following paragraphs is on another vital
data conversion integrated circuit component known as the analogue-to-digital (A/D) converter. An
A/D converter is a very important building block and has numerous applications. It forms an essential
interface when it comes to analysing analogue data with a digital computer. It is an indispensable part
of any digital communication system where the analogue signal to be transmitted is digitized at the
sending end with the help of an A/D converter. It is invariably used in all digital read-out test and
measuring equipment. Be it a digital voltmeter or a laser power meter, or for that matter even a pH
meter, an A/D converter is the heart of all of them.
An A/D converter takes at its input an analogue voltage and after a certain amount of time produces
a digital output code representing the analogue input. The A/D conversion process is generally more
complex than the D/A conversion process. There are various techniques developed for the purpose
of A/D conversion, and these techniques have different advantages and disadvantages with respect to
one another, which have been utilized in the fabrication of different categories of A/D converter ICs.
A D/A converter circuit, as we will see in the following paragraphs, forms a part of some of the types
of A/D converter.
We begin with a brief interpretation of the terminology and the major specifications that are relevant
to the understanding of A/D converters. The idea is to enable the designers to make a judicious choice
of A/D converter suitable for their application. A brief comparative study of different types of A/D
converter and the suitability of each one of these types for a given application requirement is also
discussed. This is followed by application-relevant information on some of the more popular A/D
converter IC type numbers.
12.9 A/D Converter Specifications
The major performance specifications of an A/D converter include resolution, accuracy, gain and offset
errors, gain and offset drifts, the sampling frequency and aliasing phenomenon, quantization error,
nonlinearity, differential nonlinearity, conversion time, aperture and acquisition times and code width.
Each one of these is briefly described in the following paragraphs.
12.9.1 Resolution
The resolution of an A/D converter is the quantum of the input analogue voltage change required to
increment its digital output from one code to the next higher code. An n-bit A/D converter can resolve
one part in 2
n
− 1. It may be expressed as a percentage of full scale or in bits. The resolution of an
eight-bit A/D converter, for example, can be expressed as one part in 255 or as 0.4 % of full scale or
495
and the transfer function is given by
V out /V in = R 2 /R 1 1//1 + jR 2 R 4 CCD/R 3
(12.16)
It may be mentioned here that other types of digitally controlled filter are also possible using D/A
converters. One such possibility, for instance, is by using state variable techniques, which can be used
to design D/A converter based programmable filters to get low-pass, high-pass and band-pass functions
from the same circuit.
12.8 A/D Converters
After digital-to-analogue converters, the discussion in the following paragraphs is on another vital
data conversion integrated circuit component known as the analogue-to-digital (A/D) converter. An
A/D converter is a very important building block and has numerous applications. It forms an essential
interface when it comes to analysing analogue data with a digital computer. It is an indispensable part
of any digital communication system where the analogue signal to be transmitted is digitized at the
sending end with the help of an A/D converter. It is invariably used in all digital read-out test and
measuring equipment. Be it a digital voltmeter or a laser power meter, or for that matter even a pH
meter, an A/D converter is the heart of all of them.
An A/D converter takes at its input an analogue voltage and after a certain amount of time produces
a digital output code representing the analogue input. The A/D conversion process is generally more
complex than the D/A conversion process. There are various techniques developed for the purpose
of A/D conversion, and these techniques have different advantages and disadvantages with respect to
one another, which have been utilized in the fabrication of different categories of A/D converter ICs.
A D/A converter circuit, as we will see in the following paragraphs, forms a part of some of the types
of A/D converter.
We begin with a brief interpretation of the terminology and the major specifications that are relevant
to the understanding of A/D converters. The idea is to enable the designers to make a judicious choice
of A/D converter suitable for their application. A brief comparative study of different types of A/D
converter and the suitability of each one of these types for a given application requirement is also
discussed. This is followed by application-relevant information on some of the more popular A/D
converter IC type numbers.
12.9 A/D Converter Specifications
The major performance specifications of an A/D converter include resolution, accuracy, gain and offset
errors, gain and offset drifts, the sampling frequency and aliasing phenomenon, quantization error,
nonlinearity, differential nonlinearity, conversion time, aperture and acquisition times and code width.
Each one of these is briefly described in the following paragraphs.
12.9.1 Resolution
The resolution of an A/D converter is the quantum of the input analogue voltage change required to
increment its digital output from one code to the next higher code. An n-bit A/D converter can resolve
one part in 2
n
− 1. It may be expressed as a percentage of full scale or in bits. The resolution of an
eight-bit A/D converter, for example, can be expressed as one part in 255 or as 0.4 % of full scale or