In this tekst I will be explaining the influence of f (frequency) and V (core voltage) of the CPU on it's power consumption and power (heat) dissipation.[/b]
CPUs are made in
HC-MOSFET technology. It stands for
High-speed
Complementary
Metal
Oxide
Semiconductor
Field
Effect
Transistor.
As you know, CPU consists of transistors. Those transistors make logic gate (AND, OR, NOT, NAND, NOR, XOR, XNOR). The most simple gate is NOT gate or an inverter. Inverter consists of 2 transistors.
inverter
As you can see in the picture above, it consists of 2 FET-s. One is N-channel and other is P-channel. They are configured complementary. FET-s are used as switches. They are controlled with gate (G). Gate is connected to Vin. When the FET is ON it conducts electric current from S (source) to D (drain) or from D to S. When the FET is OFF, it does not conduct current. Vdd is the supply voltage (if you want, core voltage, or positive voltage). The simbol on the bottom is GND (electrical ground, or negative voltage if you want to call it that). Vin is the input and Vout is the output (for the data which are logical levels). Logical levels are 1 (Vin or Vout connected to Vdd) and 0 (Vin or Vout connected to GND).
The way that inverter works is as follows. When you have logical 0 on the input, you will get logical 1 at the output, and vice versa. So, when Vin is 0, N-channel FET is OFF and the P-channel FET is ON. Effectively, Vout is than connected to Vdd trough P-channel FET, and you have logical 1 at the output. When Vin is 1 (connected to Vdd) than then P-channel FET is OFF and the N-channel FET is ON, and you have logical 0 at the output because Vout is connected to GND trough N-channel FET.
Now, when you have logical 0 or 1 at the input/output, that inverter does not use much power (practically nothing).
But, at the point when you have transitions from logical 0 to 1 or from 1 to 0, at the brief time period, both FET-s are ON. So current can flow from Vdd to GND, which means that you have
short circuit. When you have short circuit, you have enormus ammount of current flowing from positive to negative terminal of the power supply, because you dont have any resistance restricting it.
It is this current that is responisble for high CPU power consumption and heat dissipation (heating).
There is no way to avoid this in the HC-MOSFET technology.
The time period of the short circuit current is determined by the Vdd voltage.
The higher the voltage, the longer the time period is. The longer the time period,
the higher CPU power consumption and heat dissipation is.
Also, if CPU runs
at the higher frequency (f), you will have that short circuit current more times per second, which means that you will have
higher power consumption and heat dissipation. Even if you haven't incresed the CPU voltage.
, da malo razbijem akademski karakter rasprave
