Contents
1 ADC Structure in the MSC12xx Devices 3
2 Standard ADC Calibration Procedures ..4
3 What Affects ADC Offset?..5
3.2 A/D Conversion Formula ...13
4 Offset Compensation Methods ...14
4.2 Device Offset Calibration Commands ..14
4.3 Using Offset DAC ...15
4.4 Offset Compensation by Swapping Inputs 16
4.5 Offset Subtraction from ADC Result.16
4.6 Placing Necessary Offset Value in OC Register 17
4.7 Calculation During Program Design State.17
5 The Null_Offset Program..19
6 Recommendations.20
References20
Figures
Figure 1. MSC121xx ADC structure.4
Figure 2. ADC Offset from PGA Gain and Temperature, Buffer On ..6
Figure 3. ADC Offset from PGA Gain and Temperature, Buffer Off ..6
Figure 4. ADC Offset after Self-Calibration, from PGA Gain and Temperature, Buffer On ....7
Figure 5. ADC Offset after Self-Calibration, from PGA Gain and Temperature, Buffer Off....7
Figure 6. ADC Offset from Input Pins, Buffer ON..9
Figure 7. ADC Offset from Input Pins, Buffer OFF9
Figure 8. ADC Data, PGA Gain = 128..10
Figure 9. ADC CMRR from PGA Gain, Buffer On 11
Figure 10. ADC CMRR from PGA Gain, Buffer Off 11
Figure 11. ADC PSRR from PGA Gain..12
Figure 12. Offset DAC INL. ....15
Tables
Table 1. ADC Sampling Frequency from the PGA Gain4
Table 2. Digital Filter Bit Shift Gain Value and Decimation Ratio ...13
Table 3. ODAC codes ....16