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[Video] Moortec In-Chip Monitoring Thermal Guard-banding

January 19, 2019, anysilicon

In the first of a series of new whiteboard videos, Moortec CEO Stephen Crosher discusses Thermal Guard-banding in terms of the accuracy of embedded in-chip temperature sensors for advanced node CMOS technologies from 40nm down to 7nm.

 

There are a number of benefits if you are able to accurately sense and control your die temperature, these benefits come about through power saving, optimisation of the device and reliability.

 

Thermal guard-banding is a very important consideration for design teams. The example in the video above shows two different temperatures sensors, both uncalibrated, one slightly more accurate, one slightly less accurate. We have a temperature scale of die temperature, we have a target temperature of 85°C. In terms of setting the software to take action, whether that’s to slow down clock frequencies in order to bring the temperature of the device down or maybe to set a thermal/temperature alert within the software.

 

I you have a target temperature of 85°C and your temperature sensor is say +/- 5°C accurate you then have a set point or a range of temperatures that can vary between 90°C and 80°C so your software will need to be set at its lowest point (worst case point) to 80°C, so then allowing for the inaccuracy of the temperature sensor again, so we are compounding this issue we still have to allow for the +/- 5°C so then the lowest point actually becomes 75°C. So now if we take a more accurate temperature sensor with an accuracy of +/-2°C, again uncalibrated you then have a temperature range of 87°C and the lower part of the range being 83°C. So if you are setting your software to take action at that level then you still have to take into account the inaccuracy which is +/-2°C so that comes down to 81°C.

 

The important point is we are now comparing the lowest set point for software at 81°C with a good temperature sensor and for a less accurate temperature sensor it is 75°C. So just by using a slightly better temperature sensor in this case you could be saving yourself 6°C of die temperature.

 

So what does that mean for the customer? Depending on architecture and application, 6°C better accuracy could mean anything between 5 and 10 Watts of power saving. What that means in terms of power saving for battery operated applications such as IoT and consumer you can extend the battery lifetime. For datacentre or telecoms applications you can optimise speed and throughput of the device, and for Automotive it can increase the reliability of the devices because you are then able to help mitigate issues to do with stress and electro-migration on the devices.

 

 

Accurate thermal sensing is part of Moortec’s in-chip monitoring subsystem solutions.

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