relaxation oscillator

[double_ramp]

cmos relaxation oscillator

Hi,

I have to design a [cmos] relaxation oscillator. Can somebody please post a schematic?

Thx.

 

[little-nemo]

relaxation oscillator for low frequency

Hi,

can you please give us some specifications for your oscillator. I would guess that it is a low frequency oscillator (some MHz).
Does your oscillator be temperature independant ?

 

[double_ramp]

cmos relaxation oscillators

Hi,

yes, it should oscillate in a low frequency range, and should be temperature independent, too.

My actual design mainly looks like that:

https://www.ee.ucla.edu/~brweb/papers/Journals/BRMar96.pdf Figure 18a

With my design the problem is that it's very temperature dependent. For decreasing the frequency, I decrease the power of the oscillator which makes it temperature dependent. Now, I'm stuck with the problem at the moment.

Maybe has somebody a great idea and can post a picture or a link. It would be very helpful...

Thanks.

 

[little-nemo]

Your oscillator could not be temperature independent. The frequency is clearly dependent on the Vth of your MOS. The Vth will drift with temperature.
The only solution I know is using some voltage and/or current reference. But of course, that will increase your current consumption.

 

[ytliang]

one suggestion i would give is to use RC in between one of the inverters. Be sure to pick 2 types of resistors (positive TC and negative TC) to cancel out the temperature coefficient. Although this is not completely temperature independent, it is a decent but not too complicated approach in my opinion.