Can I use Inverter as level shifter? if no? why?

[gangadharn]

Please help to find an best answer for following question:
Can I use inverter as level shifter? If no why?

 

[galilei]

I think you can. But be careful about:

1) If it's a level-up shifter(say, 2.5V -> 3.3V), you need to increase the w/l of NMOS, and decrease the w/l of PMOS, in order to achieve an equalizatioin of rising time and falling time.

2) If it's a level-down shifter(say, 3.3V -> 2.5V), you need to tie the substrate of PMOS to the vdd of input domain. In this case, 3.3V.

3) Think *VERY* careful about the power up sequence. Does 3.3V comes first or 2.5V comes first? Your shifter may be false if power up sequence is wrong.

 

[checkmate]

The main issues are the assymetrical rise/fall times, as well as maintaining SOA on the invertor.

 

[prcken]

i think for 3.3V to 1.8V/1.2V, is possible. for 1.8V/1.2V to 3.3V, dont do that, half of 3.3V is 1.65, 1.8 with -10% variation is 1.62, maybe the input high is still low for input magin with 3.3V VDD.

 

[love_analog]

inverter can be used when going from high to low (as long as you mantain reliability)

You cannot use it when going from low to high because the pmos won't switch off.

you could make the inverter skewed, ie a very large nmos and small pmos but make sure you sim over split skew lots (fnsp and snfp)

 

[gangadharn]

Thanks to all for your answer.