Intel's analog experts will get a chance to show how they power processors with billions of transistors at the next month's International Solid State Circuits Conference.
Analog engineers need to feed high-end CPUs hundreds of amperes without starting fires. The Intel CPU processor has always been a challenge because it relies on as many as eight multi-phase switching regulators (aka DC-DC converters) per CPU, each generating up to 25 watts per chip. They are typically clocked at 250 kHz, and they generate quite a bit of heat.
DC-DC converters are pulse generators whose outputs are filtered and summed to effect currents of hundreds of amps at fixed voltages. Designers and users believe that higher switching frequencies will make incremental increases in energy-transfer efficiency and dramatic reductions in the size of ancillary components such as inductors and capacitors. Thus far, 10MHz has been the upper for commercial pulse-width modulators capable of putting out 40A from a thimble-sized package.
In ISSCC session 26 on processor power management, Intel will describe a module with an-order-of-magnitude higher clock rate. It is a fully integrated, digitally controlled buck voltage regulator with on-die inductors with a planar magnetic core on a 14nm CMOS substrate.
Technology-circuit co-optimization enables ultra-thin packages, the Intel paper reports. The module obtains a power density of 1A/mm2 and an efficiency of 84% at a switching frequency of 100MHz using a digital pulse-width modulation scheme with an 8ps resolution.
Including inductors, the modulators footprint is only 0.42mm2. The analogy I frequently use to describe DC-DC is to imagine a bulldozer moving a mountain of dirt across a road. Each shovel-full may take several minutes to transfer, and a significant amount of dirt (a measure of inefficiency) is left behind.
Now, imagine a shovel the size of a teaspoon, but with an ability to move a million scoops of dirt per second. An 100-MHz oscillator can be quite unstable, and only a fistful of companies are now claiming that kind of energy transfer rate even though faster switch rates enable significant increases in power densities.
Engineers face trade offs in increasing power density at the expense of energy transfer efficiency and vice versa. The historical trend is shown in the chart below. We are closing in on a 1-watt per mm2 power density and efficiencies of 82% in the state of the art for DC-DC converters, according to ISSCC organizers.
DC-DC converter efficiency over time with the latest results in red. (Image: ISSCC)
Because they are a must-have for practically all electronic systems, power management ICs are the largest and fastest growing segment of the general-purpose analog market, accounting for almost $12 billion in revenues. Thus power management is arguably the most significant analog skill set today.
ISSCC also will showcase analog skills in signal amplification and conditioning. General-purpose amplifiers are having a renaissance with the proliferation of devices for the Internet of Things where they a called upon to capture and elevate a low-level sensor signal to something that can manipulated by a microcontroller. Amplifier circuits account for roughly $3.5-$4 billion in annual semiconductor revenues.
Power transistors are also deserve mention. They are current delivery mechanisms used in conjunction with low-frequency power amplifiers like audio or motor drive circuits or as current switches in DC-DC converters such as voltage regulators with switch-mode outputs.
The power transistor market is about $10 billion, half of it in MOSFET switches. The most attention-getting part of the power transistor market are the Gallium Nitride (GaN) switches which promise an order of magnitude improvements in switching speed. That’s a boon to switching power supplies with higher currents and energy-transfer efficiencies that are wrestling with gate driver topologies, yet another topic in analog sessions at the event.
—Stephan Ohr is a former director for analog research at Gartner and former editor-in-chief of Planet Analog.