We use an all-digital temperature sensor architecture, that relies on a new subthreshold oscillator (achieved using the auxiliary cell “Header Cell“) for realizing synthesizable thermal sensors. We choose frequency as the temperature dependent variable. So, we use a ring oscillators that is based on inverters only and stacked native IO devices for better line sensitivity.
Figure 1: Thermal Sensor Block Diagram
Since the subthreshold current has an exponential dependency on the temperature, the frequency generated from the subthreshold ring oscillator is also dependent on temperature. Using this principle, we can sense the temperature by comparing the clock generated from a reference oscillator and the clock frequency from our proposed frequency generator. Below are the targeted user spec ranges for which the TEMP_GEN tool can output a correct design in TSMC 180nm and TSMC 65nm technology nodes:
Temp Sensor Input Spec Ranges
|Detection Range||-20⁰C – 125⁰C|
|Freq. of operation||100Hz – 10MHz|
IDEA & POSH Integration Exercises – January 2019 Demo
Video 1 shows the generation of a temperature sensor design using the TEMP_GEN tool. Based on the user spec input, the design parameters (number of cells and stages) are changed automatically. The final design is then synthesized and placed to generate a completely placed temperature sensor.
Video 1: TEMP_GEN tool