Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5510 Microcontroller Family Reference Manual, Rev. 1
Freescale Semiconductor
31-83
Preliminary
31.5.6.2
Example Calculation of Calibration Constants
The raw results obtained when sampling reference voltages 25%VREF and 75%VREF were, respectively,
3798 and 11592. The results that should have been obtained from the conversion of these reference
voltages are, respectively, 4096 and 12288. Therefore, using
, the gain
and offset calibration constants are:
GCC=(12288-4096)/(11592-3798) = 1.05106492-> 1.05102539
1
= 0x4344
OCC=12288-1.05106492*11592 -2 = 102.06-> 102 = 0x0066
shows, for this particular case, examples of how the result values change according to GCC
and OCC when result calibration is executed (CAL=1) and when it is not (CAL=0).
31.5.6.3
Quantization Error Reduction During Calibration
shows how the ADC transfer curve changes due to the addition of two to the MAC output
during the calibration - see MAC output equation in
Section 31.4.5.4, “ADC Calibration Feature
.”
The
maximum absolute quantization error is reduced by half leading to an increase in accuracy.
1. This calculation is rounded down due to binary approximation.
Table 31-43. Calibration Example
Input Voltage
Raw result (CAL=0)
Calibrated result (CAL=1)
Hexadecimal
Decimal
Hexadecimal
Decimal
25% VREF
0x0ED6
3798
0x1000
4095.794
75% VREF
0x2D48
11592
0x3000
12287.486