Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5510 Microcontroller Family Reference Manual, Rev. 1
Freescale Semiconductor
31-61
Preliminary
31.4.5.4
ADC Calibration Feature
31.4.5.4.1
Calibration Overview
The eQADC provides a calibration scheme to remove the effects of gain and offset errors from the results
generated by the on-chip ADC. Only results generated by the on-chip ADC are calibrated. The main
component of calibration hardware is a multiply-and-accumulate (MAC) unit, one per on-chip ADC, that
is used to calculate the following transfer function which relates a calibrated result to a raw, uncalibrated
one.
CAL_RES = GCC * R OCC + 2;
where:
•
CAL_RES is the calibrated result corresponding the input voltage V
i
.
•
GCC is the gain calibration constant.
•
RAW_RES is the raw, uncalibrated result corresponding to an specific input voltage V
i
.
•
OCC is the offset calibration constant.
•
The addition of two reduces the maximum quantization error of the ADC. See
“Quantization Error Reduction During Calibration
Calibration constants GCC and OCC are determined by taking two samples of known reference voltages
and using these samples to calculate their values. For details and an example about how to calculate the
calibration constants and use them in result calibration refer to
Section 31.5.6, “ADC Result Calibration
Once calculated, GCC is stored in ADC0_GCCR (see
Section 31.3.4.4, “ADC0 Gain Calibration Constant
”) and OCC in ADC0_OCCR(see
Section 31.3.4.5, “ADC0 Offset Calibration
”) from where their values are fed to the MAC unit.
A conversion result is calibrated according to the status of CAL bit in the command that initiated the
conversion. If the CAL bit is asserted, the eQADC will automatically calculate the calibrated result before
sending the result to the appropriate RFIFO. If the CAL bit is negated, the result is not calibrated, it
bypasses the calibration hardware, and is directly sent to the appropriate RFIFO.
31.4.5.4.2
MAC Unit and Operand Data Format
The MAC unit diagram is shown in
. Each on-chip ADC has a separate MAC unit to calibrate
its conversion results.
