Explaining Adaptive Voltage Scaling And Dynamic Voltage Frequency Scaling

A Q&A with Moortec CTO Oliver King.

What exactly do we mean by Adaptive Voltage Scaling versus Dynamic Voltage Frequency Scaling?

Adaptive Voltage Scaling (AVS) involves the reduction of power by changing the operating conditions within an ASIC in a closed loop. Dynamic Voltage Frequency Scaling (DVFS), on the other hand, is a power management technique where the voltage is increased or decreased depending upon dynamic (voltage, temperature) and static (process) in-chip conditions. Both are instrumental in optimising in-chip conditions in different ways.

You can use a DVFS scheme once to take process into account, or you can use it over time to account for temperature and even ageing. It is possible, for example, to reduce power consumption to achieve a desired speed of operation. It is also possible to take process variation across a die into account, which is being done in large SoCs today.

How can AVS & DVFS be used to optimise in-chip conditions?

A closed loop AVS system uses certain structures within the chip to provide the data required to adaptively track the behaviour of the silicon. By using a delay chain that has the same operating voltage as the surrounding chip, the voltage frequency relationship for the chip for that frequency is calculated by measuring the frequency of the delay chain.

Using these schemes in-chip means that variations in response to process can be compared and fluctuations in temperature can be monitored while the chip is operating. A relationship can then be observed between voltage-frequency and the reduction in power dissipation for the circuit under that specific condition which enables designers to push the levels of optimisation and reliability, allowing them to get as much performance out of the chip as possible.

What are the specific applications of AVS & DVFS?

AVS has applications associated with in-chip variability compensation by optimizing the voltage on the go to take in chip conditions into account for operation. It can also be used to set thermal alarms and initiate fan operation. Operating at higher speed (performance) will obviously lead to a shorter life time whereas operating at optimum speed will improve the device life time and therefore increase its reliability.

DVFS, on the other hand, can be used in a number of in-chip applications, including wafer sorting based on Look Up Tables (LUT). It can also be used to check functionality by decrementing the supply in regular steps as well as finding the lowest center functional voltage. The voltage can then be set to just the right level for utilising optimum power and reliability of the devices.

What is the significance of AVS & DVFS in embedded PVT Monitoring?

Increased process variability of advanced node CMOS technologies has become a significant factor to the development of SoC devices when designing for speed and power performance. Self-determination of device temperature, supply voltage levels and its own manufactured process characteristics, primarily for performance optimisation schemes (Dynamic Voltage and Frequency Scaling, DVFS) on a PER DIE basis, is becoming a compelling notion to the development community. To also measure aging effects of the silicon and analyze critical timing and supply conditions on advanced node devices, especially FinFET, from embedded sensors now makes sense.

The Voltage Monitor provides the means for advanced node integrated circuit (IC) developers to accurately measure core supply domain voltages on advanced node digital MOS devices. Voltage Monitors are specifically targeted to enable high performance Adaptive Voltage Scaling (AVS) schemes as well as providing a means for accurate IR drop analysis. The monitor is capable of monitoring multiple supply domains and can also be used to generate low voltage alarms as well as providing real-time supply data.

In-chip temperature sensors are used for performance optimisation, an example being DVFS where, depending on the thermal conditions, system clocks and voltage supplies can be varied to optimise either the speed of logical operations or power consumed by the device.

Monitors are now a critical component to advanced node chip design. Similar to other design arenas such as automotive, telecommunications, aerospace, industrial and technologies within the home, the inevitable direction of progress is to satisfy the designers’ appetite for higher sensor placement densities, higher accuracy, higher resolution and easy-to-integrate solutions. Why? Well, that’s an easy one to answer – consumers simply want higher performance and better reliability within their chosen technology products.