Data Conversion Circuits – D/A and A/D Converters
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12.9.11 Code Width
The code width is the quantum of input voltage change that occurs between the output code transitions
expressed in LSBs of full scale. Code width uncertainty is the dynamic variation or jitter in the code
width owing to noise.
12.10 A/D Converter Terminology
Some of the more commonly used terms while interpreting the specifications and salient features of
A/D converters are briefly described in the following paragraphs.
12.10.1 Unipolar Mode Operation
In the unipolar mode of operation, the analogue input to the A/D converter varies from 0 to full-scale
voltage of one polarity only.
12.10.2 Bipolar Mode Operation
An A/D converter configured to convert both positive and negative analogue input voltages is said to
be operating in bipolar mode.
12.10.3 Coding
Coding defines the nature of the A/D converter output data format. Commonly used formats include
straight binary, offset binary, complementary binary, 2’s complement, low byte and high byte.
12.10.4 Low Byte and High Byte
In A/D converters with a resolution greater than eight bits, some products are offered in high-byte or
low-byte format to simplify their interface with eight-bit microprocessor systems. The low-byte output
contains the least significant bit and some or all of the lower eight bits of the A/D converter output. In
the high byte, the output contains the MSB and some or all of the upper eight bits.
12.10.5 Right-Justified Data, Left-Justified Data
Data bit sets shorter than eight bits are placed in byte-oriented data output format, starting with the
right side of the data output transfer register. This could apply to the upper or lower byte. For example,
a 12-bit ADC will have four extra bits which could be right justified. Data bit sets shorter than eight
bits are placed in left-justified data, starting with the left side of the data output transfer register. This
could apply to the lower or upper byte. For example, a 12-bit ADC will have four extra bits which
could be left justified.
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12.9.11 Code Width
The code width is the quantum of input voltage change that occurs between the output code transitions
expressed in LSBs of full scale. Code width uncertainty is the dynamic variation or jitter in the code
width owing to noise.
12.10 A/D Converter Terminology
Some of the more commonly used terms while interpreting the specifications and salient features of
A/D converters are briefly described in the following paragraphs.
12.10.1 Unipolar Mode Operation
In the unipolar mode of operation, the analogue input to the A/D converter varies from 0 to full-scale
voltage of one polarity only.
12.10.2 Bipolar Mode Operation
An A/D converter configured to convert both positive and negative analogue input voltages is said to
be operating in bipolar mode.
12.10.3 Coding
Coding defines the nature of the A/D converter output data format. Commonly used formats include
straight binary, offset binary, complementary binary, 2’s complement, low byte and high byte.
12.10.4 Low Byte and High Byte
In A/D converters with a resolution greater than eight bits, some products are offered in high-byte or
low-byte format to simplify their interface with eight-bit microprocessor systems. The low-byte output
contains the least significant bit and some or all of the lower eight bits of the A/D converter output. In
the high byte, the output contains the MSB and some or all of the upper eight bits.
12.10.5 Right-Justified Data, Left-Justified Data
Data bit sets shorter than eight bits are placed in byte-oriented data output format, starting with the
right side of the data output transfer register. This could apply to the upper or lower byte. For example,
a 12-bit ADC will have four extra bits which could be right justified. Data bit sets shorter than eight
bits are placed in left-justified data, starting with the left side of the data output transfer register. This
could apply to the lower or upper byte. For example, a 12-bit ADC will have four extra bits which
could be left justified.