VLSI: Energy Dissipation in Semiconductor Components

This lecture discusses the energy dissipation in Very Large Scale Integration (VLSI) chips, focusing on the subthreshold current in NMOS transistors. The instructor presents an exercise involving a chip with 1 billion NMOS transistors, all in a closed state with a gate voltage of 0V. The subthreshold current is calculated, revealing a total consumption of 4 mA despite no transistors being active. The lecture further explores the implications of reducing the threshold voltage from 0.5V to 0.25V, demonstrating how this change significantly increases the subthreshold current to 5.7 nA per transistor. The instructor emphasizes the challenges of managing power consumption in microprocessors, where the majority of transistors remain inactive. The discussion highlights the importance of maintaining an appropriate threshold voltage to prevent excessive power dissipation, which could lead to overheating and failure of the chip. The lecture concludes with simulations showing the impact of different threshold voltages on current consumption, reinforcing the need for careful design in VLSI systems.