Unified Power Format (UPF) Design - key Points

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1) Is Isolation Needed Between ON and OFF (Standby) Blocks?

  • Typically, isolation is essential between OFF-to-ON blocks. However, in certain situations, implementing isolation from ON-to-OFF domains is also recommended.
  • The isolation strategy between OFF-to-ON domains is commonly referred to as Parking.
  • This approach is particularly important for special signals with multiple loads in the OFF (Standby) domain, such as RESET or CLK signals.
  • It ensures these signals remain stable and do not toggle while the domain is in the OFF state.
  • By preventing unnecessary switching of sequential elements in the OFF domain, this strategy significantly reduces power consumption.

2) What is the Basic Low Power Sequence Followed in Modern VLSI Design?

The fundamental sequence for entering and exiting low power modes is as follows:

  • Save outputs of retention registers
  • Activate isolation control signals (enable isolation)
  • Enable clock gating
  • Apply power gating or shut down power to specific blocks
  • Wait for a predetermined time or event (e.g., an interrupt) to exit low power mode
  • Remove power gating and power up the domain
  • Restore retention register values
  • Disable clock gating (ungate the clock)
  • Release isolation signals

3) What are the Benefits of Using ELS (Enable Level Shifter) Cells When Both Isolation and Level Shifter Cells Exist Separately?

  • ELS cells integrate isolation and level shifting functionalities, resulting in a more area-efficient design.
  • This combined approach reduces silicon area usage compared to using separate isolation and level shifter cells.

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