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In a circuit design, wrong connectivity may cause undesired leakage paths that may result in current hotspots. These current hotspots can be quickly identified with Spectre’s dynamic design checks. This blog describes how to use the Spectre design checks to identify the root cause of the leakage path current hotspots.
Current Consumption in Digital Designs
In digital CMOS designs, the consumption of power supply current is typically very low because the current is consumed only when the digital circuitry is switching. During switching, the current flows from VDD to GND in a very short time. However, most of the time there is no switching, and therefore, the current is near zero, as shown in the below figure.
A faulty connectivity in a digital design may cause a high continuous leakage current, as shown below.
The Spectre dynamic design checks help identify the root cause of such unwanted leakage path currents. The following figure shows a mixed-signal design with the critical leakage current path in red.
Spectre Dynamic Subcircuit Power Check
Spectre provides a dynamic subcircuit power check, dyn_subcktpwr, which reports the power supply current consumption of each block of a design, ordered from highest to lowest. For a faulty design, we can use this check to identify the block that consumes the large leakage current. Once the block is known, its connectivity can be checked and fixed.
pwr1 dyn_subcktpwr net=dvdd depth=15
Spectre Dynamic Leakage Path Check
If the problematic design block that consumes most of the leakage current is small, after running the dyn_subcktpwr check, we can analyze and fix the design problem in this small block. However, if the block is large containing hundreds or more elements, it may be a challenge to identify the elements that cause the leakage current. For such cases, we can use the Spectre dynamic leakage path check, dyn_dcpath, to report the leakage path with all the elements in the path.
dcpath1 dyn_dcpath net=[dvdd 0] ith=100u duration=0.1u
In this blog, we discussed how to use the Spectre dynamic subcircuit power and leakage path checks to identify the root cause of the unwanted leakage path currents in a design. Please refer the Spectre “Detecting Leakage Path Current Hotspots with Spectre” application note for more details.
You may also contact your Cadence Support AE for guidance.
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