How to design an low noise amplifier (BW<1K) that has very low input refer noise (or very low offset) ? I think Autozero and Chopping is not good enough. If I can use offchip JFET like LSK (**broken link removed**), how to do the following design?
Also, I found an ultra low noise OpAmp from TI (OPA228: http://focus.ti.com/docs/prod/folders/print/opa228.html), the input referred noise is only 3nV/srHz, how can they do that?
As I know, AD797 is also a very low-noise opamp. If you use CMOS, it is difficult to reach this spec. I guess they have special technologies to support the low-noise design.