Cross-layer investigation of continuous-time sigma-delta modulator under aging effects

In order to achieve reliability study in large and complex analog and mixed signal (AMS) circuits and systems, it is required to develop effective reliability-aware design methodologies and exploration tools. This paper discusses two aging mechanisms: hot carrier injection (HCI) and negative bias temperature instability (NBTI) and their effect on 65 nm CMOS integrated circuits and systems (ICs). We propose an aging-aware cross-layer approach to comprehensively evaluate aging induced performance degradation at the abstraction (system) level. This approach is composed by hierarchical aging analysis at transistor/circuit level, block failure analysis at abstraction level and system-level aging considerations, which can essentially highlight sensitive blocks for circuit designers. This approach is demonstrated with a continuous-time (CT) sigma-delta (ΣΔ) modulator. Analog loop filter and clock distributor are studied with failure boundary and transistor level aging simulation. The aging investigation approach reports system level aging-aware consideration of these building blocks. Results show that amplifiers in analog loop filter have enough margin to cope with aging induced degradations. However, aging risk exists in clock circuits, especially when implementing with high ^Vt transistors. NBTI induced clock jitter from clock distributor can influence clocked block in CT ΣΔ modulator and degrade signal-to-noise ratio (SNR).