Why CPU has so many power supply pins (e.g. Vcc, Vss)?
We know that most of the electronic ICs have a maximum of two pins for supply, one is Vcc or Vdd and another is GND or Vss or Vee. But CPU has so many power supply pins. So, the question is arise, why CPU has so many power supply pins.
There some very very
important reasons for using so many power supply pins in CPU which are given
below.
Current Handling
CPU pins are generally made
using Ball Grid Array(BGA) technology. So the BGA balls are not capable to
conduct a very high amount of current. Suppose a CPU dissipates 100 watts of
power. So if the Vdd is 1V, then the current will be (100/1) = 100 Ampere of
current.
So a single BGA ball cannot
handle 100A current. If 100A current is transferred using a single BGA ball
then the following problems will occur.
1.
Very Hig
Voltage drop which will reduce the input voltage.
2.
Large
heat produces.
3.
High loss
occurs.
So if a multiple no. of Vdd
pins are used, then this problem will be solved. If we use 200 Vdd pins then
the current per pins will be (100A/200) = 0.5A which is more reliable and
efficient.
Different Voltage Levels
CPU has many circuits such
as many digital modules, high-speed drivers inside it. So all the circuit are
not working at the same voltage level. To provide the different voltage levels
different pins are used. The arrangement of providing different voltage or
power to the different circuit inside the CPU is called power integrity. So
Power Integrity and Signal Integrity are very important factors for using
multiple pins.
Inductance Effect
It is seen that after
examination when a single pin is used for power supply, the pin act as an
inductor. As the CPU operate in very high frequency, the pin produces more
inductance effect. Inductance effect causes sudden changes in power drawn by
the CPU. As a result, the CPU behaves incorrectly.
We know that when the
inductors are connected in parallel, the total equivalent inductance is very
smaller than the individual inductance. So when a multiple no. of pins are used
for power supply the inductance effect decrease.
Impedance
The impedance effect is
seen where the inductance and capacitance are present. So using so many pins
for power supply reduces the Impedance of the power supply coming into the
chip. This also helps to reduce the noise and other issues during the high
impulsive transient loading.
Power Distribution
Using so many pins for
power supply to CPU helps to power distribution to all circuits inside the CPU.
If a single pin is used for power supply, then the power is to be distributed
from that single pin to all the circuits, therefore the length of the wire will
increase in order to route the power supply to different modules inside the CPU
which makes the circuit more complex, bigger.
Read Also:
- [Explained] Main Components of CPU and their Functions
- Mobile CPU VS Desktop CPU | The Actual Difference
- Difference between Microprocessor and Microcontroller and CPU
- Concepts of Semiconductor Memory in Digital Circuit
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Why CPU has so many power supply pins (e.g. Vcc, Vss)?
Reviewed by manoranjan das
on
8:50 am
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