SLYY222 November 2023 ADC12DJ5200RF , ADS127L11 , BQ79731-Q1 , REF35 , REF70 , TPS62912 , TPS62913 , TPS7A20 , TPS7A94 , TPSM82912 , TPSM82913
- 1
- Overview
- At a glance
- Noise and ADCs
- Defining noise and precision in a power architecture
- Innovations in low-noise and low-power voltage references
- Innovations in ultra-low-noise voltage references
- Improving noise and thermal performance with simplified power architectures
- High-current low noise with LDO supply rails
- Innovations in precision battery monitoring
- Conclusion
- Additional resources
Noise and ADCs
Noise in an ADC can cause errors in precise voltage measurements. You must consider the total contribution of noise in the signal chain from internal and external sources. Total noise is often a combination of ADC thermal noise, ADC-quantization noise, amplifier noise, voltage-reference noise and power-supply noise.
Equation 1 depicts the total referred noise at the input of the ADC (at full-scale voltage) as it measures the sensor based on Figure 1. The main design challenge is to optimize all noise sources to achieve the noise target that the application requires. In Equation 1, the ADC’s power-supply rejection ratio (PSRR) reduces the power-supply noise, which is plotted out to 1 MHz:
Given the existence of uncorrelated noise sources, the total noise is the root sum square of all sources, which heavily favors the largest noise source. One noisy component can heavily skew the measurement. For example, if a voltage reference contributes more noise than an ADC and power supply, reducing noise on the voltage reference will be the best way to lower the system noise, as shown in Figure 2 and Figure 3. In addition, ADC noise types vary with resolution: quantization noise is significant for a 16-bit ADC, but you can ignore it for a 24-bit ADC.
Figure 2 Voltage reference dominant noise.
Figure 3 ADC thermal dominant noise.