Pulse width with negative temperature coefficient

[mike_bihan]

I was designning a pulse generator ( ring oscillator);

The spec need the period to have negative temperature coefficient.
The hotter, the shorter the period.

If I used a RC delay to form the pulse width, the coefficient will be positive because the resistor will be more resistive.

MOS working close to sub-threshhold region have negative coefficient however, I have no idea to implement.

Any idea? Any paper?

thanks,

 

[Humungus]

If your design is in IC, some technologies offer a hiresistive poly which has negative temperature coefficient. You could also use a MOS resistor biased under its ZTC (Vt decreases with temperature). You could use a PTAT current source instead of a resistor.

 

[rtpq]

If you want NTC pusle width instead of NTC frequency, why generate a ramp and NTC/PTC voltage? You can use a comparator to generate the pusle.

 

[mike_bihan]

Humungus:

Yeah, it is the direction. However, in detail implementation plan will be more complex. The bias voltage will be very sensitive below ZTC point.

PTAT might be a nice idea.

Any good article on that?

thanks,