HCS08 datasheet(228/290 Pages) MOTOROLA

228 / 290 page

Analog-to-Digital Converter (ATD) Module

MC9S08GB/GT

228

MOTOROLA

•

Integral non-linearity (INL) — This is the difference between the transition voltage to the current

code and the transition to the corresponding code on the adjusted transfer curve. INL is a measure

of how straight the line is (how far it deviates from a straight line). The adjusted ideal transition

voltage is:

•

Zero scale error (EZS) — This is the difference between the transition voltage to the first valid code

and the ideal transition to that code. Normally, it is defined as the difference between the actual and

ideal transition to code $001, but in some cases the first transition may be to a higher code. The ideal

transition to any code is:

•

Full scale error (EFS) — This is the difference between the transition voltage to the last valid code

and the ideal transition to that code. Normally, it is defined as the difference between the actual and

ideal transition to code $3FF, but in some cases the last transition may be to a lower code. The ideal

transition to any code is:

•

Total unadjusted error (ETU) — This is the difference between the transition voltage to a given code

and the ideal straight-line transfer function. An alternate definition (with the same result) is the

difference between the actual transfer function and the ideal straight-line transfer function. This

measure of error includes inherent quantization error and all forms of circuit error (INL, DNL,

zero-scale, and full-scale) except input leakage error, which is not due to the ATD.

•

Input leakage error (EIL) — This is the error between the transition voltage to the current code and

the ideal transition to that code that is the result of input leakage across the real portion of the

impedance of the network that drives the analog input. This error is a system-observable error which

is not inherent to the ATD, so it is not added to total error. This error is:

EIL (in V) = input leakage * RAS

There are two other forms of error which are not specified which can also affect ATD accuracy. These are:

•

Sampling error (ES) — The error due to inadequate time to charge the ATD circuitry

•

Noise error (EN) — The error due to noise on VAIN,VREFH,orVREFL due to either direct coupling

(noise source capacitively coupled directly on the signal) or power supply (VDDAD,VSSAD,VDD,

and VSS) noise interfering with the ATD’s ability to resolve the input accurately. The error due to

internal sources can be reduced (and specified operation achieved) by operating the ATD

conversion in wait mode and ceasing all IO activity. Reducing the error due to external sources is

dependent on system activity and board layout.

(Current Code - 1/2)

Adjusted Ideal Trans. V =

* ((VREFH + EFS) - (VREFL + EZS))

(Current Code - 1/2)

Ideal Transition V =

*(VREFH – VREFL)

(Current Code - 1/2)

Ideal Transition V =

*(VREFH – VREFL)

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