sx8725 Semtech Corporation, sx8725 Datasheet - Page 46

• Manufacturer Part Number: sx8725
• Description: Sx8725 Zoomingadc? For Pressure And Temperature Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
Gain Error and Offset Error
Gain error is defined as the amount of deviation between the ideal transfer function (theoretical Equation 18)
and the measured transfer function (with the offset error removed).
The actual gain of the different stages can vary depending on the fabrication tolerances of the different
elements. Although these tolerances are specified to a maximum of 3%, they will be most of the time around
maximal error in the same direction in all stages is very low. Finally, these gain errors can be calibrated by the
software at the same time with the gain errors of the sensor for instance.
Figure 26 shows gain error drift vs. temperature for different PGA gains. The curves are expressed in % of Full-
Scale Range (FSR) normalized to 25° C.
Offset error is defined as the output code error for a zero volt input (ideally, output code = 0). The offset of the
ADC and the PGA1 stage are completely suppressed if NELCONV > 1.
The measured offset drift vs. temperature curves for different PGA gains are depicted in Figure 27. The output
offset error, expressed in LSB for 16-bit setting, is normalized to 25° C. Notice that if the ADC is us ed alone, the
output offset error is below 1 LSB and has no drift.
V1.5 © 2007 Semtech Corp.
0.5%. Moreover, the tolerances between the different stages are not correlated and the probability to get the
Figure 27 - Offset Error vs. Temperature for Different PGA Gains
Figure 26 - Gain Error vs. Temperature for Different PGA Gains
-0.1
-0.2
-0.3
-0.4
100
0.2
0.1
0.0
-20
-40
80
60
40
20
0
-50
-50
ZoomingADC™ for Pressure and Temperature Sensing
NORMALIZED TO 25° C
NORMALIZED TO 25° C
-25
-25
Temperature [°C]
Temperature [°C]
0
0
46
25
25
50
50
75
75
1
5
20
100
1
5
20
100
100
100
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SX8725