Why is that IO pads operate at higher voltage than core?

[mvvijay78]

Hi,
What is the function of IO pads that are used along with standard cells.Why is that they operate at a much higer voltage than core.Do they also act as level converters other than providing ESD protection.
regards
Vicky

 

[diablo1222]

For digital I/O, it include the lever convert function.

 

[ecijun]

speed

 

[haosg]

the pcb board load of pad is about 10 pf, high voltage can provide high-speed.

 

[aegean.chou]

compatible with old device

 

[eltonjohn]

In the cpu core speed dendend ultimatly on the time to go from logic 0 to 1 and from 1 to 0 .having a low voltage makes this transition faster .so the cpu can work faster .But with the io you want a good level signal to improve the noise/signal ratio .

 

[luxboy]

If asic, almost customer demonded

 

[jaxshai]

I think it is depended on your applications.
Most foundry could provide different I/O for customers. such as 3.3/3.3 and 3.3/5.0.

 

[rakko]

mostly for 2 reasons; one is drive strength of standard cells are limited so using standard cells to drive package pin and heavy board traces will degrade signal quality to the point of making them unusable. IO cells are build to have heafty drive capability generally around 5-10pF. second is most board and ICs still run at higher voltage usually 2.5-3.3 volts. this is mainly because the thick traces on the board and from standard ICs are large and therfore have huge capacitances associated with them. If these traces are driven by 1.0 volt core voltage, the signal will be degraded due to board noise and beomes unusable.

 

[Hughes]

Hi,
What is the function of IO pads that are used along with standard cells.Why is that they operate at a much higer voltage than core.Do they also act as level converters other than providing ESD protection.
regards
Vicky

For one thing, we need to lower the core supply voltage to minimize the power dissipation.
For another thing, we need a higher voltage for IO pads because:
1) The IC should be compatible with other circuits on the board.
2) The noise margin is larger with larger supply voltage.