SSD Architecture

Flash cards, USB keys and Solid State Drives are definitely the most known examples of electronic systems based on non-volatile memories, especially of NAND type .

Several types of memory cards (CF, SD, MMC, …) are available in the market , with different user interfaces and form factors, depending on the needs of the target application: e.g. mobile phones need very small-sized removable media like μSD.

SSDs are the emerging application for NAND. A SSD is a complete, small system where every component is soldered on a PCB and is independently pack- aged: NANDs are usually available both in TSOP and BGA packages.

A basic block diagram of a Solid State Drive is shown in Fig. 1.1. In addition to Flash memories and a microcontroller, there are usually other components. For instance, an external DC-DC converter can be added in order to derive the internal power supply, or a quartz can be used for a better clock precision. Of course, reasonable filter capacitors are inserted for stabilizing the power supply. It is also very common to have a temperature sensor for power management reasons. For data caching, a fast DDR memory is frequently added to the board: during a write access, the cache is used for storing data before transfer to the Flash. The benefit is that data updating, e.g. in routing tables, is faster and does not wear out the Flash.

In order to improve performances, NANDs are organized in different Flash channels, as shown in Fig.