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

• Published in: IEEE transactions on circuits and systems. I, Regular papers Vol. 55; no. 11; pp. 3480 - 3487
• Main Authors: Keller, M., Buhmann, A., Sauerbrey, J., Ortmanns, M., Manoli, Y.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2008; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analog-digital (A/D) conversion; cascaded; Circuit stability; Circuits; Compensation; Complexity theory; continuous time (CT); Delay; Delay effects; Digital modulation; Digital-analog conversion; Dynamic range; excess loop delay (ELD); Feedback; Joining; Modulators; multi-stage nose shaping (MASH); Network topology; Operational amplifiers; Optimization; Performance analysis; sigma-delta (\Sigma\Delta); Stability; Analog-digital (A/D) conversion; MASH; continuous time; sigma-delta; excess loop delay; ELD; cascaded
• ISSN: 1549-8328; 1558-0806
• DOI: 10.1109/TCSI.2008.925362

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.