MCP3021
4.5
Differential Non-Linearity (DNL)
4.8
Gain Error
In the ideal ADC transfer function, each code has a uni-
form width. That is, the difference in analog input volt-
age is constant from one code transition point to the
next. DNL specifies the deviation of any code in the
transfer function from an ideal code width of 1 LSB.
The DNL is determined by subtracting the locations of
successive code transition points after compensating
for any gain and offset errors. A positive DNL implies
that a code is longer than the ideal code width, while a
negative DNL implies that a code is shorter than the
ideal width.
The gain error determines the amount of deviation from
the ideal slope of the ADC transfer function. Before the
gain error is determined, the offset error is measured
and subtracted from the conversion result. The gain
error can then be determined by finding the location of
the last code transition and comparing that location to
the ideal location. The ideal location of the last code
transition is 1.5 LSBs below full-scale or V
.
DD
4.9
Conversion Current (I
)
DD
The average amount of current over the time required
to perform a 10-bit conversion.
4.6
Integral Non-Linearity (INL)
4.10 Active Bus Current (I
)
INL is a result of cumulative DNL errors and specifies
how much the overall transfer function deviates from a
linear response. The method of measurement used in
the MCP3021 ADC to determine INL is the “end-point”
method.
DDA
The average amount of current over the time required
2
to monitor the I C bus. Any current the device con-
sumes while it is not being addressed is referred to as
Active Bus current.
4.7
Offset Error
4.11 Standby Current (I
The average amount of current required while no con-
version is occurring and while no data is being output
(i.e., SCL and SDA lines are quiet).
)
DDS
Offset error is defined as a deviation of the code transi-
tion points that are present across all output codes.
This has the effect of shifting the entire A/D transfer
function. The offset error is measured by finding the dif-
ference between the actual location of the first code
transition and the desired location of the first transition.
The ideal location of the first code transition is located
2
4.12 I C Standard Mode Timing
2
I C specification where the frequency of SCL is
at 1/2 LSB above V
.
100 kHz.
SS
2
4.13 I C Fast Mode Timing
2
I C specification where the frequency of SCL is
400 kHz.
DS21805A-page 14
2003 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
