Thanks, I see that there is a medium Vth nmos and pmos with threshold voltages 200mV and 250mV respectively.
If my power supply is about 0.6V then could you suggest a good topology?
I want to use it for the current reference here.
Why would you want a switched topology? Do you already have the comparison voltages VH and VL available? And the comparator and RS-FF working at 0.6V supply?
I'd prefer a simple architecture like the Vittoz current reference: .
What frequency are you looking for? I'm designing a similar circuit at the moment. As the delay of the feedback loop is temperature dependent I suggest to go for a dual phase system to chancel out this delay. Especially when you want frequencies above 100kHz.
Edit: You only need one reference voltage within a dual phase system.
I'm designing an oscillator that works with the same principle. You don't necessary need an OpAmp for this circuitry. Like erikl suggested you can use self biased mos-only circuitry to generate the reference current and the reference voltage. Therefore you can go for very low power (If needed).