MCP3910 datasheet(63/90 Pages) MICROCHIP

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DS20005116D-page 63

MCP3910

At low signal amplitude values (typically 1000:1

dynamic range and higher), the crosstalk between

channels, mainly caused by the PCB, becomes a sig-

nificant part of the perturbation as the measurement

error increases. The 1-point measurement error curves

in Figure 2-5 have been performed with a full-scale

sine wave on all the inputs that are not measured,

which means that these channels induce a maximum

amount of crosstalk on the measurement error curve.

In order to avoid such behavior, a 2-point calibration

can be put in place in the calculation section.

This 2-point calibration can be a simple linear interpo-

lation between two calibration points (one at high

amplitudes, one at low amplitudes at each end of the

dynamic range) and helps to significantly lower the

effect of crosstalk between channels. A 2-point calibra-

tion is very effective in maintaining the measurement

error close to zero on the whole dynamic range, since

the nonlinearity and distortion of the MCP3910 is very

low. Figure 2-6 shows the measurement error curves

obtained with the same ADC data taken for Figure 2-5,

but where a 2-point calibration has been applied. The

difference is significant only at the low end of the

dynamic range, where all the perturbing factors are a

bigger part of the ADC output signals. These curves

show extremely tight measurement error across the full

dynamic range (here, typically 10,000:1), which is

required in high-accuracy class meters.

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