Subthreshold region Ring OSC temperature effect

[lsfeng]

Hi All,

When I　design a current starved low power ring osc, I find the frequency goes up with the temperature increasing and it is quite different from my previous experiences.

After careful investigation ,I find the mosfet is working in sub-threshold region, and so it switches from sub-threshold region to off region during stable oscillation.

Do I have any risk to design this kind ring oscillator ? It 's seems it is a must to use sub-threshold design for low power design .

 

[artmalik]

No this is not a good idea at all. I am assuming that you are interested in the generating some kind of clock. The current starved inverter(digital gate) ring oscillator are used mainly to change the frequency using a Vref signal which can be adjusted. So depending upon the temp,vdd and process your design can be made to generate a certain frequency.

Using anything is subthreshold operation means it is heavily dependent on the process and temp variation. So just for low power going into subthreshold operation is not worth it. People use subthreshold operation for small medical devices which get implanted in human body(you cant cut open a person to change the battery everytime) or in space(less power needs).... otherwise not worth it