What is an always-on cell in VLSI?

An always-on cell (AON) in VLSI is a type of digital circuit that is designed to remain powered on and active even when the main power supply to the device is turned off. These cells are typically used in low-power applications, such as mobile devices, IoT devices, and other battery-powered electronic devices where it is necessary to maintain certain functions even when the device is in a low-power or standby mode.

AON cells are usually responsible for tasks such as maintaining real-time clocks, monitoring external events, and maintaining the state of the device when it’s in sleep mode. They are also used in power management circuits to monitor the status of the battery and to shut down the device before the battery drains completely.

AON cells are typically designed using specialized low-power logic gates and flip-flops that consume very little power when the device is in standby mode. They also employ a number of power management techniques such as voltage scaling, dynamic voltage, frequency scaling, and power gating to minimize power consumption.

Overall, AON cells play an important role in enabling the development of low-power and energy-efficient electronic devices and systems.