how to keep state if a low to high levelshifter's low voltage down ?

[michaeljackson]

Hi all,

In our SOC, analog part works in 3.3V, and digital part works in 1.8V. Our power down mode needs digital part sending power down signal to power down analog circuits. So 1.8V to 3.3V levelshifter is needed.

If I sim the level shifter with 1.8V down and 3.3V unchanged, the state keeps. But test result shows that if 1.8V down, the state will be wrong, i.e,
if levelshift outputs 1 before 1.8V down, then it will outputs 0 after 1.8V down.

I put the schematic in the attachment , can anyone give some advice? thanks !

 

[erikl]

I'd think your active input pair M0,M1 is too strong in comparison to the cross-coupled keeping pair M7,M8 (91:3).

 

[michaeljackson]

Hi erikl, This circuit needs strong input pair ,maybe it is too strong. But I didnot find the correct size.

 

[erikl]

Just try and make the keeping pair M7,M8 stronger!