NXP Semiconductors MC9S08QL4, Reference Manual

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Analog-to-Digital Converter (S08ADC12V1)
MC9S08QL8 MCU Series Reference Manual, Rev. 1
NXP Semiconductors 147
• Integral non-linearity (INL) — This error is defined as the highest-value the (absolute value of the)
running sum of DNL achieves. More simply, this is the worst-case difference of the actual
transition voltage to a given code and its corresponding ideal transition voltage, for all codes.
• Total unadjusted error (TUE) — This error is defined as the difference between the actual transfer
function and the ideal straight-line transfer function and includes all forms of error.
10.6.2.6 Code Jitter, Non-Monotonicity, and Missing Codes
Analog-to-digital converters are susceptible to three special forms of error. These are code jitter,
non-monotonicity, and missing codes.
Code jitter is when, at certain points, a given input voltage converts to one of two values when sampled
repeatedly. Ideally, when the input voltage is infinitesimally smaller than the transition voltage, the
converter yields the lower code (and vice-versa). However, even small amounts of system noise can cause
the converter to be indeterminate (between two codes) for a range of input voltages around the transition
voltage. This range is normally around ±1/2 lsb in 8-bit or 10-bit mode, or around 2 lsb in 12-bit mode,
and increases with noise.
This error may be reduced by repeatedly sampling the input and averaging the result. Additionally the
techniques discussed in
Section 10.6.2.3 reduces this error.
Non-monotonicity is defined as when, except for code jitter, the converter converts to a lower code for a
higher input voltage. Missing codes are those values never converted for any input value.
In 8-bit or 10-bit mode, the ADC is guaranteed to be monotonic and have no missing codes.