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3.3. Data Correction
There are two errors which affect the DC accuracy of the ADC and DAC. The first is the zero error (offset). For
the ADC this is the data value when converting with the input connected with its own ground in single ended
mode, or with shorted inputs in differential mode. For the DAC it is the data value required to produce a zero
voltage output signal. This error is corrected by subtracting the known error from all readings.
The second error is the gain error. Gain error is the difference between the ideal gain and the actual gain of the
programmable gain amplifier and the ADC, respectively DAC. It is corrected by multiplying the data value by a
correction factor.
The data correction values are obtained during factory calibration and are stored in the modules individual ver-
sion of the ID PROM. The ADC has a pair of offset and gain correction values for each of the programmable gains.
The DAC has a pair of offset and gain correction values for each single output channel.
The correction values are stored in the ID PROM as two’s complement byte wide values in the range -128 to
127. For higher accuracy they are scaled to ¼ LSB.
3.3.1. ADC Correction formula
The basic formula for correcting any ADC reading is:
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Value is the corrected result, Reading is the data read from the ADC, Gain
corr
and Offset
corr
are the correction
factors from the ID PROM.
Gain
corr
and Offset
corr
correction factors are stored for each for the possible gain settings.
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Summary of Contents for TIP850
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