Today’s successive-approximation-register (SAR) analog-to-digital converters (ADCs) and sigma-delta ADCs are known for their high resolution and low noise. Nevertheless, achieving signal-to-noise (SNR) performance specified in the datasheet can be difficult. An even greater challenge is optimizing ADC spurious-free dynamic range (SFDR) by establishing a reliable noise floor without incurring spurs in the system signal chain. Such spurs are often caused by improper circuitry surrounding the ADC, or can result from external interference, especially in harsh operating environments.
This article will describe techniques for identifying the root causes of spur issues in high-resolution, precision ADC applications, and offer solutions to solve them while improving end-system EMC capability and reliability. Use cases include spurs caused by dc-dc power-supply radiation, ac-ac adapter noise, analog input cable noise, and room lighting.
Spurs and SFDR
It’s common knowledge that spurious-free dynamic range (SFDR) represents the smallest power signal that can be distinguished from a large interfering signal. For current high-resolution, precision ADCs, the SFDR is typically dominated by the dynamic range between a fundamental frequency and the second or third harmonic of the fundamental frequency of interest. However, certain spurs can limit the performance due to other aspects of the system.