Design OpAmp with low supply voltage

[anhnha]

I would like to design an OpAmp with TSMC018 with a very low supply voltage (about 0.5V). Could anyone suggest some topologies?
Thank you.

 

[erikl]

Won't be simple: TSMC18 transistors have threshold voltages of around |0.4|V, the min. length devices rather |0.5|V. No headroom.

Or do you think of a special low Vth option (which needs about 6 more masks and 4 more implants)? Not cheap.

 

[anhnha]

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.

 

[erikl]

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: .

From: Alice Wang, Benton Highsmith Calhoun, Anantha P. Chandrakasan, Sub-threshold Design for Ultra Low-Power Systems
© 2006 Springer Science+Business Media, LLC, 233 Spring Street NY 10013
Chap. 8: Analog Circuits in Weak Inversion by Eric A. Vittoz
8.4 Exponential Characteristics
8.4.1 Voltage and Current Reference, p. 156

 

[anhnha]

Thank you for the help. I will study the architecture. But do you think that it is not as good as the one I gave above?

Why would you want a switched topology?

I want to use it (ramp generator) for my boost converter.

Do you already have the comparison voltages VH and VL available?

Not yet.

And the comparator and RS-FF working at 0.6V supply?

Yes.

 

[erikl]

But do you think that it is not as good as the one I gave above?

I want to use it (ramp generator) for my boost converter.

You didn't tell before, what for you'd need it. Yes, I think your topology is quite ok for your purpose.

 

[NiedeLu]

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.

 

[anhnha]

Hi,
My frequency is only 100kHz. You meant that you are designing OpAmp or boost converter?

 

[NiedeLu]

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).