4 ms·

> The only problem is that the anmount of electrons you have to push through the transistors has a quadratic dependence on frequency. I don't see how this is u

> The only problem is that the anmount of electrons you have to push through the transistors has a quadratic dependence on frequency. I don't see how this is ultimately true. The amount of electrons needed to flip a capacitor is constant given that the voltage is constant. The more often you flip, the more current you need per time. The amount of electrons needed to flip a capacitor is proportional to the voltage. So, lower voltage means a) less power per electron and b) less electrons. Therefore the power is quadratic with the operating voltage. Third, if you want to increase the frequency, at some point, you have to increase the voltage or you get errors. Then you increase frequency and voltage at the same time and your power consumption shoots up.

nom 10y ago
Hmm maybe I'm wrong. I vividly remember an equation for the power consumption of a CPU, and it definitely had a f^2 in it. However, I currently can't derive it anymore (and it was definitely a simplification). I'll try to pull up the slides later. It's probably outdated, the influence of the individual factors may have changed. In the meantime I can only offer this [1] stackexchange post. Power of a CPU is definitely quadratic in f, or even worse. [1] http://physics.stackexchange.com/questions/34766/how-does-power-consumption-vary-with-the-processor-frequency-in-a-typical-comput http://physics.stackexchange.com/questions/34766/how-does-po... edit: I probably remembered it wrong and I now think that that the equation was P=C x V^2 x f. However, transition power effectively has an exponent much greater than 2, but that's apparently caused by the increased die temperature (according to the post on Anandtech).
- static_noise 10y ago
  That linked thread on Anandtech digs in quite a bit. The real physics involved is, of course, more complex than my simple model. Instead of a square dependence, they find the 5th power of the supply voltage. I believe this has to do with how the transistors are designed which creates a lot of wasted current at higher voltages. The square dependence would show with perfect transistors.

nom 10y ago

Hmm maybe I'm wrong. I vividly remember an equation for the power consumption of a CPU, and it definitely had a f^2 in it. However, I currently can't derive it anymore (and it was definitely a simplification). I'll try to pull up the slides later. It's probably outdated, the influence of the individual factors may have changed. In the meantime I can only offer this [1] stackexchange post. Power of a CPU is definitely quadratic in f, or even worse. [1] http://physics.stackexchange.com/questions/34766/how-does-power-consumption-vary-with-the-processor-frequency-in-a-typical-comput http://physics.stackexchange.com/questions/34766/how-does-po... edit: I probably remembered it wrong and I now think that that the equation was P=C x V^2 x f. However, transition power effectively has an exponent much greater than 2, but that's apparently caused by the increased die temperature (according to the post on Anandtech).

static_noise 10y ago
That linked thread on Anandtech digs in quite a bit. The real physics involved is, of course, more complex than my simple model. Instead of a square dependence, they find the 5th power of the supply voltage. I believe this has to do with how the transistors are designed which creates a lot of wasted current at higher voltages. The square dependence would show with perfect transistors.