Constructing DRAM circuits with MOSFETs
A single bit in a standard dynamic random-access memory (DRAM) integrated circuit is composed of two circuit elements: a MOSFET and a capacitor. The following section presents a brief introduction to the electrical characteristics of capacitors.
The capacitor
A capacitor is a two-terminal passive circuit element capable of storing energy. Energy enters and leaves a capacitor as electrical current. The voltage across the capacitor terminals is proportional to the quantity of electrical energy contained in the capacitor.
To continue the hydraulic system analogy introduced in Chapter 2, Digital Logic, think of a capacitor as a balloon attached to the side of the pipe leading to a water tap. Water pressure in the pipe causes the balloon to inflate, filling it with some of the water from the pipe. Let’s assume this is a strong balloon, and that as it inflates, the balloon stretches, increasing the pressure within. The balloon fills...
