MAC7200 datasheet(855/976 Pages) FREESCALE

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Initialization/Application Information

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

777

can be seen that the TUE has been successfully halved with the disadvantage that the maximum TUE

occurs at the beginning and the end of the transfer curve.

33.12.2.1.3

Gain Error Correction via OCC and GCC (Gain Too High)

It depends on the application whether the gain error correction is done only via GCC, only via OCC or

with both. The advantage of changing both is that the TUE can be made constant until Vx is reached (see

blue dotted line in Figure 33-23b). In this case TUEmax is the same as when changing OCC only.

33.12.2.1.4

Gain Error Correction via Warp (Gain Too High)

In Section 33.12.2.1.1, “Gain Error Correction via GCC (Gain Too High)” and Section 33.12.2.1.2, “Gain

Error Correction via OCC (Gain Too High)” it was shown how the TUE can be reduced by doing a

numerical adjustment via GCC and OCC.

Beside this numerical adjustment the ATD has another feature: Warp. This feature will influence the

analog behavior of the conversion circuit. It will adjust the gain and the offset by a fixed value which is

completely independent of OCC and GCC:

Figure 33-24a assumes a gain error (blue line) with gain too high. By enabling the warp-feature the gain

error is reduced and the offset is increased. Usually the error is overcompensated (green curve in

Figure 33-24a). Therefore it is necessary to correct the remaining TUE via GCC and OCC. For further

details please see Section 33.12.2.1.5, “Gain Error Correction via GCC (Gain Too Low)”.

Figure 33-24. Gain Error (Gain Too High) Compensated via Warp

TUEmax

VRH-VRL

VANx

Counts

0xFFF

VRH-VRL

Ideal transfer

curve

Gain too high

Adjusted

0x000

TUE [counts]

VANx

via warp

TUEmax

VRH-VRL

VANx

Counts

VRH-VRL

Ideal transfer

curve

Gain too high

Adjusted

0x000

TUE [counts]

VANx

via warp and

TUEmax

a) Gain adjustment via warp

b) Gain adjustment via warp an: OCC < 0

GCC / OCC

0xFFF

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