Hi,
 I might sound strange, but it is possible to generate a supply/temperature independent reference without using band-gap. This is for an ADC.

Thanks,
SBR

You can do it from any number of sources, for example the Vt of a mosfet added to a PTAT source, but usually these references are not PROCESS independent. There is only one process independent reference available: the PTAT voltage generated by differing current densities in a bipolar transistor. The next best thing is the bipolar transistor base-emitter voltage, which is well behaved over process. When you add the two together you can always trim the result to a "magic voltage" of about 1.2V that is temperature stable. There is nothing out there that compares to that robustness over process.

Other methods: putting a voltage onto a floating gate has been published a few times in the last few years. I'm skeptical of the lifetime of these things, but what do I know... Buried Zener references were an old standby (better than bandgap references), but supply voltages are probably too low in your process. And using MOSFET Vts, but I don't think that gives a "magic voltage" to trim to. A long time ago there was an article in JSSC about using the difference between a "native" MOS and one that had the threshold adjust, but it isn't used much.

That said, you don't need to create a bandgap circuit to generate the reference. E.G. if you want a current, just sum up a VBE and PTAT current. Also, in the charge domain, you can get the same effect of sampling a 1.2V constant "bandgap" reference by sampling a properly weighted combination of PTAT and VBE voltages. You can even do this with one bipolar transistor and a two-level current source if you are clever.

In the end though, it is really hard to beat using the combination of PTAT and VBE to create a reference.

rg

"not possible" is not the way I would put it... more likely performance is degraded when the temperature is cold and the voltage supply is 0.8V. For supplies of 0.85V and 0^oC bandgap in the traditional sense (delta Vbe & Vbe) is easily achieved.

Does that the ADC itself start suffering performance degradation with 0.8V irrespective of the bias ? If the ADC needs extremely accurate bias to operate under the specified conditions, then maybe its the ADC which needs modification ?