What to look out for when selecting an Embedded Temperature Sensor.
When selecting an embedded temperature sensor for use within your digital SoC it is important to make sure it ticks certain boxes.
Listed below are the 6 key things to look out for:
You can’t beat accuracy! Improved accuracy is an opportunity for a higher level of optimisation and reliability. If your sensor accuracy is just 1 degree Celsius more accurate, you can expect reasonable power savings through the lifetime of your product. Be cautious as some analog macros offering high thermal sensing accuracy may also consume more silicon real estate.
Keep the cost of your silicon down. Increased area leads to increases in your bottom-line product cost. This is where sensor size and specification can be traded-off to address the primary requirement demanded by the end application. Do you need a robust temperature sensor to raise an alert when things get too hot, or do you need highly accurate sensing for a fine-grain DVFS scheme?
To keep production test costs down, ensure that any testing associated with the sensor is kept to a minimum. So ensure that the temperature sensor selected has easy to control test accesses (eg, SCAN, JTAG and IEEEP1500) and that a high level of test coverage is offered. If the IP needs calibration to hit accuracy specs, be wary if two-point temperature calibration is required, as this will eat into your test time budget.
During the lifetime of your chip, how do you know if your temperature sensor has failed? What would the consequences be if a stuck bit on your data output skewed your dynamic temperature measurements? A temperature sensor with self-checking on its critical functions will allow the system to make a fail safe response. Otherwise your chip, and therefore the product, could be exposed to the risk of physical damage.
5. Calibration Schemes
Not all applications will require the higher temperature sensing accuracy offered through trim or calibration. However, if calibration is needed then IP with complex and slow calibration schemes will increase the cost of your products and should be avoided. Ensure it has a quick, single-temperature-point calibration scheme that is easy for your production test team to implement. It will be even better, if your temperature sensor calibration scheme does not require any knowledge of the ambient temperature and can be calibrated at any temperature.
6. Easy to Integrate
Life is short and tape-out schedules even shorter. Designers are busy people, so digital interfacing offered with the thermal sensor will make the IP easier to integrate. If you want to be unpopular with your physical implementation team then choose a sensor that requires sensitive analogue signals needing to be routed! Optional interfaces such as AMBA APB and a pre-defined register map make it easier for your SoC team to integrate the IP and not have to worry themselves about dealing with proprietary interfacing and control schemes.
The in-chip thermal monitoring and management of advanced node designs has become a critical consideration for SoC developers. Ensure you clearly understand your requirement in light of the end application.
Finally, be sure to choose an IP vendor that is able to demonstrate consistent and successful circuit performance in volume production. If you have selected well, you will soon build a rapport and a good relationship with the vendor’s design team, as after all, the success of your product is a shared undertaking.