ADC SNDR and SFDR: Signal-to-Noise and Distortion Ratio Analysis

In signal processing systems, performance evaluation of Analog-to-Digital Converters (ADCs) is crucial for maintaining signal integrity. Two core parameters - Signal-to-Noise and Distortion Ratio (SNDR) and Spurious-Free Dynamic Range (SFDR) - directly reflect the conversion quality of ADCs.

SNDR (Signal-to-Noise and Distortion Ratio) measures the ratio of signal power to the sum of noise and distortion power. Its calculation typically relies on spectrum data obtained through FFT analysis: first extract the amplitude of the fundamental frequency component of the target signal, then calculate the total noise energy excluding DC components and signal harmonics. In code implementation, this involves applying window functions (like Hanning or Hamming) to ADC output data, performing FFT transformation, and implementing peak detection algorithms to identify fundamental and harmonic components. Higher SNDR values indicate lower noise and distortion introduced during ADC conversion.

SFDR (Spurious-Free Dynamic Range) focuses on the system's ability to suppress spurious signals, defined as the difference between the fundamental frequency amplitude and the maximum spurious component amplitude. Its calculation requires scanning the entire frequency domain to identify the highest interference peak excluding fundamental waves and harmonics. Algorithm implementation typically involves spectrum analysis with threshold detection and peak search routines to locate spurious components. Larger SFDR values indicate cleaner dynamic range and better anti-interference capability of the ADC.

In practical engineering applications, these parameters are commonly calculated through the following steps: apply standardized window functions to ADC output data, perform FFT transformation to obtain spectrum data, locate signal components through peak detection algorithms, and finally compute ratios or differences according to definition formulas. In high-frequency applications, special attention must be paid to spectrum leakage and quantization errors. Calibration algorithms may need to be incorporated to improve calculation accuracy, such as using coherent sampling techniques or implementing digital post-processing compensation.

Understanding the physical significance and calculation methods of SNDR and SFDR provides crucial guidance for high-speed ADC selection, signal chain design, and system performance validation. Proper implementation of these measurement algorithms in signal processing software ensures accurate characterization of ADC performance in various applications.