Researchers at the Delft University of Technology wanted to use FPGAs at cryogenic temperatures down around 4 degrees Kelvin. They knew from previous research that many FPGAs that use submicron fabrication technology actually work pretty well at those temperatures. It is the other components that misbehave — in particular, capacitors and voltage regulators. They worked out an interesting strategy to get around this problem.
The common solution is to move the power supply away from the FPGA and out of the cold environment. The problem is, that means long wires and fluctuating current demands will cause a variable voltage drop at the end of the long wire. The traditional answer to that problem is to have the remote regulator sense the voltage close to the load. This works because the current going through the sense wires is a small fraction of the load current and should be relatively constant. The Delft team took a different approach because they found sensing power supplies reacted too slowly: they created an FPGA design that draws nearly the same current no matter what it is doing.
There are two parts to this trick. First, you have to know that the FPGA voltage dropped (implying a rise in current consumption). They do this by measuring the delay through a cell. Then you have to selectively control your power consumption. To do this, their design includes 4 “farms” of 128 oscillators each. These, of course, draw power. As other parts of the chip draw more power, the FPGA turns off 4 oscillators (one from each farm) at a time to keep the power consumption constant. As the chip draws less power, of course, the oscillators will reactivate to take up the slack.