Selection of diode ratio in bandgap reference voltage?

[bharatsmile2007]

Hello everybody,
I am new to design of BGR,
The question is that the selection of diode ration(1:n).
Commonly every one prefer 1:8 to achieve good common centroid configuration in layout. But is there any ratio which is leass than 8?

Thanks inadvance.
bharat

 

[dick_freebird]

I've gone as low ad 4:1. But the higher the ratio, the stronger
your "temperature signal" will be, allowing you to use less
resistor (which is often the real driver of layout area).

 

[rfsystem]

8:1=a give nice looking layout and above 8:1 the differential voltage

Vt*ln(a)

does not increase any more significant to lower impacts from control amplifier mismatches. So it seems to be golden ratio.

A good question is what is the limit to increase the ratio "a" if there is no layout limitation.

I expect that the Vbe~log(Ic) conformance have some limits to higher current densities by parasitic resistances and to lower current densities by leakage currents. For lateral PNPs or substrate PNP's I expect at least a useable current density ratio of 1e4. So that lead to high areas.