Analog Circuit Characterization

Delivering nanometer-scale analog circuits requires increasingly intensive circuit characterization including: process/voltage/temperature (PVT) corners, parameter sweeps, and Monte Carlo statistical analysis. To more fully account for variations, designers also run combinations of these methods, such as corners with sweeps and sweeps with Monte Carlo.  

It is also critical to account for nanometer physical effects like device noise, device mismatch, and detailed parasitics during characterization, which adds considerably to characterization quantity and complexity. While analog characterization has traditionally been deterministic, e.g., running PVT corners pre-layout and post-layout, it is becoming increasingly important to more accurately analyze process variation, device mismatch, and device noise—all of which are inherently statistical. Doing so requires employing a form of statistical analysis such as Monte Carlo-based characterization. The figure below illustrates the increasing characterization requirements as designs move to smaller technology nodes.

Analog FastSPICE (AFS) is the industry’s fastest, highest accuracy, and most comprehensive platform for efficient nm analog circuit characterization. Moreover, AFS includes automation for many characterization setup and post-processing tasks:  

• Multi-Core Parallel (AFS MCP): enables up to 16 simultaneous corner, sweep, or Monte Carlo iterations using multiple cores on the same machine. AFS MCP speeds up characterization by up to 50x relative to a single-core traditional SPICE simulator, letting designers thoroughly characterize complex blocks at nm processes geometries quickly enough to meet tight project deadlines.  
• High capacity with nanometer SPICE accuracy: the AFS Platform can simulate post-layout circuits with over 10 million elements without any compromise in accuracy. This is important for selective corner characterization of top-level circuits.  
• Device Noise Analysis (DNA): AFS RF provides full-spectrum periodic noise analysis for periodic circuits like oscillators, switched-cap filters, phase detectors, and charge pumps. AFS Transient Noise Analysis provides “golden” results that correlate to within 1 to 2 dB of silicon measurements, with timestep simulation times less than twice as long as a transient-only run. The DNA Advisor helps designers set values for key noise simulation parameters that optimize performance and accuracy.  
• Advanced statistical post-processing: the AFS WaveCrave Calculator Pad (CalcPad) includes yield estimation functions based on statistical confidence intervals, which measure the uncertainty inherent in a statistical sample. Designers can quantify uncertainty with respect to sample size, which lets them quantify and trade off yield uncertainty, circuit margin, and characterization iterations.
• Multi-run post-processing: CalcPad automates setting up and executing complex measurements such as ADC SNDR, PLL jitter, and phase noise across all corners and sweeps. It produces aggregated results interactively or from the command line, and it provides a powerful basis for automated regression suites.  

The screen shot below shows a CalcPad window where designers can create post-processing templates. Designers can add signals by dragging and dropping waveforms from the AFS WaveCrave waveform processor.

With the AFS Platform, designers can perform efficient nm analog circuit characterization with confidence.

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