SBOA443 March   2021 INA293

 

  1.   Trademarks
  2. 1Introduction
  3. 2The SAR ADC Switching Model
    1. 2.1 Acquisition Time
    2. 2.2 ADC Resolution
    3. 2.3 Sample Rate
  4. 3The ADC Charge Bucket Filter
    1. 3.1 The Filter Capacitor, CFILT
    2. 3.2 Output Filter Resistor, RFILT
  5. 4Output Filter Discussion and Design
    1. 4.1 INA293 With the ADC Switching Model
  6. 5Summary
  7. 6References

ADC Resolution

ADC resolution creates a similar challenge to that of acquisition time, but on the opposing axis of quantization. When analog information is digitized, quantization error is often a primary source of error, and the magnitude of this error becomes smaller as resolution increases. However, as the error target is now smaller, the ADC is further challenged to settle to a more precise value within the acquisition time of the device. Quantization Error as a Percentage of FSR provides a quick glance at quantization error for various common ADC bit resolutions.

Table 2-1 Quantization Error as a Percentage of FSR
ADC Resolution1 LSB, FSR = 4.096VQuantization Error, % of FSR
04 mV.049%
121 mV.0122%
1662.5 µV.000763%
1815.625 µV.000190%
203.90625 µV.000048%
24244.14 nV.00000298%

Because of this relationship, as the resolution of the ADC is increased, the amount of settling time needed is increased in turn.