What are the benefits and drawbacks of using multiple voltage domains and power modes in RTL design?

1 Voltage domains

A voltage domain is a group of logic elements that operate at the same supply voltage level. By using different voltage levels for different domains, you can optimize the power-performance trade-off for each domain. For example, you can use a lower voltage level for less critical or less active domains, and a higher voltage level for more critical or more active domains. This way, you can save power by reducing the dynamic power consumption, which is proportional to the square of the voltage.

However, using multiple voltage domains also introduces some challenges and complexities. For instance, you need to ensure that the signals crossing the voltage domains are properly level-shifted, isolated, and synchronized. You also need to consider the impact of voltage variations and noise on the logic functionality and timing. Moreover, you need to manage the power distribution and delivery network, and avoid excessive voltage drops or IR drops.

2 Power modes

A power mode is a configuration of the device that defines the state of each voltage domain and the clock frequency. By using different power modes, you can adapt the device behavior to the different operating conditions and user scenarios. For example, you can use a low power mode when the device is idle or in standby, and a high performance mode when the device is active or processing intensive tasks. This way, you can save power by switching off or scaling down the voltage and frequency of the domains that are not needed or used.

However, using multiple power modes also involves some challenges and trade-offs. For example, you need to design and verify the power management logic that controls the transitions between the power modes. You also need to account for the latency and overhead of the power mode changes, and ensure that they do not affect the user experience or the system functionality. Furthermore, you need to balance the power savings and the performance requirements, and avoid frequent or unnecessary power mode switches.

3 RTL design considerations

Using multiple voltage domains and power modes in RTL design requires careful planning and analysis. You need to identify the power requirements and constraints of your device, and define the optimal number and configuration of the voltage domains and power modes. You also need to use appropriate tools and methodologies to model, simulate, and verify your RTL design with respect to the power aspects. You need to ensure that your RTL design is compatible with the downstream synthesis, implementation, and testing processes, and that it meets the functional, timing, and power specifications.

Using multiple voltage domains and power modes in RTL design can help you achieve lower power consumption and higher performance for your device. However, it also introduces some challenges and trade-offs that you need to consider and address. By understanding the benefits and drawbacks of these techniques, you can make informed decisions and design choices for your RTL design.

4 Here’s what else to consider

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