Multi Voltage Domain

Why we need the multi voltage domains in SOC, Can’t we design a chip with single voltage?
Yes we can design a chip with a single voltage when we are working on less frequency where speed is not main priority.

                                          Source : Internet

If someone is least interested in speed of operation like snail which will ultimately reach the destination but the time taken to reach the destination can be 1 hour or 5 hours, then we can design a SOC with single low voltage domain which operates at low frequency. And power consumption will be less as power is directly proportional to V²

If a person want the results in nano seconds, then the device must work at high frequency. With applying high voltage, high frequency can be achieved with a drawback of power loss, as power is directly proportional to V²

 Ex: Assume computer need to add 2 and 2, output will be 4. The time taken to execute the instruction and display the output depends on frequency of CPU, it will take more time if CPU is working on less frequency (low voltage). If the computer need to execute given instruction in nano seconds, the CPU should operate on high frequency (high voltage) with huge amount of power loss

Because of this huge power loss, it is not practical to design a SOC with single voltage domain at high frequency. To reduce the power consumption design was divided into multiple voltage or power domains each with its own supply voltage and this type of approach is called multi voltage design. The multi voltage design is based on realisation that in SOC design, different blocks will have different objectives for instance processor need to run at high speed and the processor block should be supplied with high supply voltage. On other hand USB block may run at fixed, relatively low frequency. In this case low supply voltage required for operation. Few blocks will be powered off when they are not in use.
Also multi voltages are required in RAM

• Low voltage to maintain memory contents when the memory is not being accessed
• Higher Voltage that supports read and write action

There are different Multi voltage domain strategies:

• Static Voltage Scaling (SVS)
• Multi-Level Voltage Scaling (MVS)
• Dynamic Voltage and Frequency Scaling (DVFS)
• Adaptive Voltage Scaling

To conclude, to reduce the power consumption at higher frequency, multi voltage domain is one of the technique used.