signals crossing from one voltage domain to another voltage domain

[sun_ray]

There is voltage domain V1 and there is another voltage domain V2. Here V1 is greater than V2. Now for signals passing from V1 to V2 there are need to put isolation cells and high to low level shifter. What is the sequence of placement of this high to low level shifter and the isolation cell? Will the isolation cell put first then the level shifter or it is the other way around?

 

[Nandy]

It should be V1->Isolation->LevelShifter->V2. Normal practice is to combine Isolation and LevelShifter called enable-level-shifter.

 

[sun_ray]

Can it be done in this way V1-> Level Shifter -> Isolation->V2? If not then why? What will be the sequence for signals going from V2 to V1?

Regards

 

[Nandy]

Can it be done in this way V1-> Level Shifter -> Isolation->V2? If not then why? What will be the sequence for signals going from V2 to V1?

Regards

V1-> Level Shifter -> Isolation->V2 would violate power rule. When V1 is off, Level Shifter has cell driven by power down block directly.
If V2 can be powered off as well, then V2->Isolation->Level Shifter->V1

 

[sun_ray]

But how will it be if I keep the sequence like V1-> Level Shifter -> Isolation->V2 but Level Shifter is powered by V2.

What will be the voltage domain for Level shifter for Level shifter for V1-> Isolation->Level Shifter -> V2. If the Level shifter has voltage of V1 then when V1 is off the level shifter will not get any power.

Regards

 

[Nandy]

But how will it be if I keep the sequence like V1-> Level Shifter -> Isolation->V2 but Level Shifter is powered by V2.

What will be the voltage domain for Level shifter for Level shifter for V1-> Isolation->Level Shifter -> V2. If the Level shifter has voltage of V1 then when V1 is off the level shifter will not get any power.

Regards

Level shifter and Isolation should never be powered off. For V1, there should be two domains, V1ON, and V1OFF, and the same for V2. So it is something like
V1OFF->Isolation(V1ON)->LevelShifter(V1ON/V2ON)->V2OFF

Nandy
NanDigits Design Automation

 

[sun_ray]

But how will it be if I keep the sequence like V1-> Level Shifter -> Isolation->V2 instead of your sequence? What will be the problem with this sequence V1-> Level Shifter -> Isolation->V2. Can you please elaborate?

Regards

 

[Nandy]

V1OFF to LevelShifter(V1ON) violates the power rule. Any signal from power off domain should drive isolation cell first.

 

[sun_ray]

How does V1OFF to LevelShifter(V1ON) violates the power rule? Is it that there will be crowbar current in Levelshifter and that is the violation you are talking off?

Can we make the power supply for the sequence in the following way?

V10FF->Isolation(V2ON)->LevelShifter(V1ON/V2ON)->V2OFF

Regards