A Comparative Study on Excess-Loop-Delay Compensation Techniques for Continuous-Time Sigma–Delta Modulators

Excess loop delay (ELD) is well known for its detrimental effect on the performance and stability of continuous-time sigma-delta modulators. A detailed analysis on the most recently published compensation techniques for single-stage modulators is performed in this paper, thus enabling their application to an arbitrary modulator. Based on different characteristics such as circuit complexity, achievable dynamic range, or requirements on the operational amplifiers, their advantages and disadvantages are investigated. Subsequently, the analysis is extended to cascaded modulators. Contrary to intuition, the results indicate that a compensation of ELD in every stage of the cascade is insufficient for optimal performance. Although not configured in a feedback configuration and as such not suffering from stability problems, each coupling network between two stages must additionally be compensated for ELD.