Growing demand for integrated circuits (ICs), for example microprocessors, with ever higher levels of performance and functionality have driven these devices to circuit densities beyond 100 million transistors per die. This number may soon exceed one billion transistors on a single die. The growth in transistor density has been made possible by the use of MOSFET transistors with gate lengths below 100 nm. As gate length has shortened, power supply voltages have fallen, in some cases, to below 1 V.
Advances in transistor density have enabled the introduction of microprocessors with multiple processing cores. Given the continued transistor density advances, the likely trend will be towards microprocessors with ever increasing numbers of processing cores. The term “processing cores” need not refer to symmetric cores of uniform size and capability. In the most generic sense, “processing cores” can refer to any large block of incremental computational capability.
Advances in integrated circuit (IC) technology have led to significant increases in the operational frequencies of the IC. Typically, a manufacturer of an IC designs and guarantees the IC to operate properly up to a specification maximum operational frequency, if voltage supplied to the IC is within a targeted voltage range. Generally, to reduce power consumption, it is desirable to operate the IC near the lower end of the targeted voltage range.
In addition to being dependent on the applied voltage, the operational frequency of an IC may also be dependent at least in part on the temperature of the IC, the age of the IC, and/or other factors. Thus, various environmental limits, such as, but not limited to, temperature, voltage and so forth, are specified to facilitate a system designer to manage the usage of the IC, to ensure it functions properly. These environmental limits are typically conservatively specified (guardbanded) to accommodate among other things, aging of the IC. The level of conservatism (or magnitude of the guardband) varies from manufacturer to manufacturer, depending in part on the quality experience of the manufacturer.
A CPU operating at a given frequency will draw a variable amount of current depending on the type of instructions being executed. The variation in current produces self-induced voltage noise. Since processing cores are activated only as needed, there are times when there are very few cores activated, and other times when all the processing cores are activated. The magnitude of self-induced voltage noise increases as the number of activated processing cores increases.