How to avoid overestimating or underestimating the impact of noise.
Device noise is critical in nanometer-scale CMOS processes, and it fundamentally limits the performance of many circuits at 45 nm and below. Given the right tools, device noise analysis (DNA) is a fairly straightforward process that should produce results that are within 1 dB to 2 dB of silicon measurements. However, there are a number of common mistakes that can lead to grossly overestimating or underestimating the device noise impact—leading to substantial over-design and under-design.
There are three basic types of DNA. Transient noise analysis is a statistical time-based technique that applies to every type of circuit. Transient noise analysis is the only device noise analysis applicable to non-periodic circuits. For periodic-driven circuits, such as charge pumps and switched-capacitor filters, periodic noise analysis is generally much faster and provides better diagnostic information than transient noise analysis. Similarly, for periodic autonomous circuits, oscillator noise analysis is much faster and provides better diagnostic information (e.g., device contribution and sensitivity analysis) than transient noise analysis. Since transient noise analysis is applicable to all types of circuits, it provides a good way to cross-check results for periodic circuits and oscillators. Used correctly, all of these techniques should produce results within 1 dB to 2 dB of silicon measurements.
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