power domain and voltage domain

[mr_vasanth]

What is the difference between voltage domain and power domain ?
can a single power domain can have more than multiple voltage ?
can a single voltage domain can have multiple power domains ?

There is a thread already available in edaboard about this topic. But I could not find satisfactory answer there and its a old thread.

 

[rca]

voltage domains, do not have the same voltage values so required level shifters.
power domains means, power on-off, required isolator cell.
And all mix between voltage/power domains are allow, for lof ot fun .

 

[sun_ray]

voltage domains, do not have the same voltage values so required level shifters.
power domains means, power on-off, required isolator cell.
And all mix between voltage/power domains are allow, for lof ot fun .

Does power island and power domain mean the same? Does voltage island and voltage domain mean the same?

Regards

 

[rca]

Yes island / domain, means the same (for me).
Island is more "visual" for the floorplan designer.
Domain is more for the architect designer.

 

[sun_ray]

Yes island / domain, means the same (for me).
Island is more "visual" for the floorplan designer.
Domain is more for the architect designer.

What do you mean by island is more visual for floorplan designer?

Regards

 

[rca]

Two islands are separate by sea, and so each have is own power supply.

 

[sun_ray]

Two islands are separate by sea, and so each have is own power supply.

You wrote power island is power switch on and off. So if in a voltage domain there are two power islands, these two power islands then have the two power supplies and this is not possible as in a voltage domain only one value of voltage is possible. Can you please resolve this?

Regards

 

[rca]

There are only power switch, and the value is for me "equivalent" before and after this power switch, no?
Or do you have a design with power switch which degradate so much the voltage value?

 

[sun_ray]

There are only power switch, and the value is for me "equivalent" before and after this power switch, no?
Or do you have a design with power switch which degradate so much the voltage value?

Probably the confusion is arising due to definition of the power domain. Can you please define with more details the power domain?

We basically have a power switching fabric which is on/off whenever required. What do you mean by power switch?

Do you want to mean that two power islands in the same voltage domain will have different power switching network and hence the two power islands are isolated by sea? But in that case how you write that two islands are separate by sea, and so each have is own power supply. Should not the island will work with only one power supply instead of two is the power supply value is same?

Regards

 

[rca]

What do you mean by power switch?

The switch which supply your power domain.

Do you want to mean that two power islands in the same voltage domain will have different power switching network and hence the two power islands are isolated by sea?

Yes, see upf/cpf.

 

[mr_vasanth]

Hi rca, Thanks a lot. You have helped here a lot to understand one voltage domain and multiple power domains.
I would like to hear from you about the scenario one power domain and multiple voltage domain too.

 

[sun_ray]

Do you want to mean that two power islands in the same voltage domain will have different power switching network and hence the two power islands are isolated by sea?

Yes, see upf/cpf.

Do you want to mean that the two power islands will have different separate power supply with the same voltage value instead of one single power supply? If yes, why?

Regards

 

[mr_vasanth]

hi sun_ray, relating power switches to clock gating cells may give you some idea. A single clock source can have multiple clock gating cells. Similarly a single power supply can have multiple power switches. You can compare clock enable signal that controls clock gating cell with the power on/off signal that controls the power switch.

 

[rca]

Do you want to mean that the two power islands will have different separate power supply with the same voltage value instead of one single power supply? If yes, why?

Regards

Yes, to save leakage by powering-off some part of the design.

 

[sun_ray]

Yes, to save leakage by powering-off some part of the design.

To save leakage by powering-off some part of the design, even a same single power supply can be used instead of two separate power supplies with voltage value same. We can keep one power supply and two power switching network for the two separate power islands so that we can switch off the power supply of the an island by switching off its power switching network? Why are you suggesting two different power supplies with same voltage value then? This was our question.

Regards

- - - Updated - - -

hi sun_ray, relating power switches to clock gating cells may give you some idea. A single clock source can have multiple clock gating cells. Similarly a single power supply can have multiple power switches. You can compare clock enable signal that controls clock gating cell with the power on/off signal that controls the power switch.

Do you want to mean the power switching network by power switch?

Regards

 

[rca]

that we can switch off the power supply of the an island by switching off its power switching network?

Yes

Why are you suggesting two different power supplies with same voltage value then?

I don't find in the post where I wrote that, two power supplies with different voltage values make more sense to save dynamic power in case all ip could not go at the same lowest voltage.

 

[sun_ray]

I don't find in the post where I wrote that, two power supplies with different voltage values make more sense to save dynamic power in case all ip could not go at the same lowest voltage.

You wrote of two power islands separated by sea. Did you want to mean that the two power islands will have different voltage supplies with the same voltage value? Or, did you mean that the two power islands will have same voltage supply with one voltage value?

In both cases whether it is two separate power supplies with same voltage value or one single power supply with a single voltage value there is only one voltage domain since the voltage value is same for both the power supplies.

Regards

 

[rca]

Two power islands means power on/off separatly, so 4 cases, independently of the voltage value.

 

[sun_ray]

Please answer the following question . It is to resolve the understanding difference clearly.

Question. What is beneficial between the two following scenarios and why?

A) Two power islands will have different voltage supplies with the same voltage value.
B) Two power islands will have same voltage supply with one voltage value.