I have a question on different power supplies in a integrated circuit. I have seen VDDIO supply is more than VDDCore. If the input signal is more than the power signal, won't it affect the device?? Explain the purpose of this variations..??
Electrical – Why VDDIO is more than VDDcore supply in VLSI/ integrated chips
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Best Answer
Large integrated circuits usually have multiple power planes to meet the requirements of different parts of the circuitry on the chip. Splitting core and I/O supplies onto separate rails is quite common. This is done so that the core can be built with smaller transistors that offer the best possible performance characteristics (higher density, smaller parasitics, lower power consumption, faster switching speed, etc.) while the I/O circuitry requires larger transistors and higher voltages to drive signals off-chip and interface with the outside world.
It also enables independent adjustment of the core voltage, enabling power-saving features such as DVFS (dynamic voltage and frequency scaling), which is common in low power devices such as cell phones. Using an adjustable voltage regulator for the core voltage enables lowering both the core voltage and core clock frequency to save significant power when high performance is not required.
Separate power supplies can also be used for noise reasons - sensitive analog circuitry including PLLs, serializers, deserializers, RF interfaces, etc. will usually also get dedicated power pins to reduce noise either into or out of these components.
It is also possible to have multiple different IO voltages connected to different sets of IO pins, enabling a chip to interface with other circuitry that is running with different voltage levels.