Frequency vs voltage

[sara1983]

Hi,
Suppose I have an ASIC which runs at 4Ghz clock and at a particular voltage... I increase the frequency to 6Ghz....why do I have to increase the voltage.... ?? can someone please explain the relationship between operating frequency and voltage... ??

Thanks!
Satish R

 

[crutschow]

I have no idea, since we know nothing about the ASIC.
There is no general relation between operating frequency and supply voltage.
Circuits don't generally need a change in voltage with operating frequency, so this must be something particular to the ASIC.

 

[BradtheRad]

Applied voltage has a relation to slew rate. So in that sense, greater voltage may be a way to obtain faster slew rate. On the other hand the greater voltage makes a greater span to travel between supply rails. This extends the travel time, so do we gain or lose? Not sure.

 

[sara1983]

It's something got to deal with the heat... can someone explain the relationship between heat generated ,operating voltage and frequency.... ??

 

[BradtheRad]

Overclocking enthusiasts speed up a cpu by running it at a faster frequency. It causes the chip to get hotter than normal. This problem arises due to transistors not being able to snap instantly between On and Off. Instead the faster frequency causes them to spend a larger percentage of cycles traveling in a middle range, wasting power and generating heat.

If the devices were only totally Off or totally On, they'd tolerate being driven at the higher frequencies, with no additional heat production.

 

[c_mitra]

It's something got to deal with the heat... can someone explain the relationship between heat generated ,operating voltage and frequency.... ??

You are right.

Total energy of a sine wave is dependent on the frequency. You can consider it like you have to put it on and off more often when the frequency is higher. An ideal switch does not need energy to turn on and off but all real switches do.

This is true for sine waves too - because the oscillators are not ideal, they have some losses and this loss is proportional to the frequency. Just consider the switching losses in a transistor at higher frequency.

To partly compensate for the losses, you must use a higher voltage. If other things stay the same, higher voltage will permit a faster switching on and off.

Of course you will have more losses - higher frequency and higher voltage. So this consideration (argument or logic) cannot be extended too far.

 

[ThisIsNotSam]

Hi,
Suppose I have an ASIC which runs at 4Ghz clock and at a particular voltage... I increase the frequency to 6Ghz....why do I have to increase the voltage.... ?? can someone please explain the relationship between operating frequency and voltage... ??

Thanks!
Satish R

Because transistors are faster if overdriven. But your question is backwards. It should be: why can I increase the frequency if I increase the supply voltage?

This is a very simplified answer though. Covered in undergrad courses.