New strategies in removing non-coherency from signals with large distortion to noise ratios

Signal spectral analysis is a dominating way of characterizing the dynamic performance of analog signals. To perform accurate spectral testing, the IEEE Standard 1241, 1658 and 1057 suggest coherent sampling. Obtaining coherent sampling, especially when signals have large distortion to noise ratios, has been a challenge for many years. With the growing need for Built-In-Self-Test (BIST) circuits for lower test cost, achieving coherent sampling is becoming more and more challenging. For signal analysis, the signals under test don't usually have sufficient purity. On-chip oscillators, such as Wien Bridge oscillators and Ring oscillator don't possess high signal purity. For high speed, low resolution DACs, the output signal purity is also low. In that case, not only fundamental bin will have spectral leakage, harmonic bins will also have spectral leakages, which makes non-coherency harder to remove.