Evolution of PVT IP: From Analog Mixed Signal (AMS) to Digitally Assisted Analog (DAA) Architecture

As process technology continues to evolve, so must the IP that complements the SoCs using them. One example of an industry evolution is on the PVT monitoring IP side. The process, voltage, and temperature (PVT) monitors embedded within chips provide feedback on silicon status at every stage of the lifecycle, and most importantly while in mission-mode use in the field. The data gathered from the monitors enables adaptive/dynamic SoC performance optimization along with secondary benefits such as early prediction of impending chip failures and tracking of trends across a “fleet” of chips deployed worldwide.

Today the advent of the AI revolution has led to an insatiable need for high performance computing for inference and LLM training and the foundries have stepped up to fulfill and meet the challenge of hyper Moore’s law. Today these big leaps are being made possible by the building block of the digital age: the gate-all-around (GAA) transistor. Unfortunately, the classic Bipolar junction transistor that has been the pillar of analog design for half a century has been getting fewer updates or is being eliminated in the new foundry processes geared towards high performance compute that is digital.

The design of PVT monitoring IP must undergo a major rethink to stay ahead of the curve and adapt to the advent of the GAA transistor. The current lack of thick oxide MOSFET device makes BJT based designs impractical since they operate at higher voltages around 1.2v. In some processes BJT is eliminated resulting in the need to use MOSFET or thermal resistor as a sensing element. This shift in sensing technology is pushing us away from AMS architecture for PVT IP. Simply put, adapt and evolve or become irrelevant fast. 

Digitally Assisted Analog (DAA) architecture has the benefit of not only a smaller area and lower power, but it also eliminates the need for shielding signal lines from the effect of noise/crosstalk needed for analog signals. Lower accuracy for DAA IP will be the main trade-off compared to AMS IP, however System on Chip (SoC) architects will be able to insert these IPs closer to actual intended points due to their smaller size, resulting in equivalent effective accuracy gains by eliminating proximity errors, thereby negating their own inherent accuracy limitations because of their digital nature.

Analog Mixed Signal (AMS) and Digitally Assisted Analog (DAA) designs both integrate analog and digital circuitry on a single chip, but they differ fundamentally in their design approach and the role of the digital part.