Using nvSRAMS to supercharge flash memory devices in data-logging applications
Many of today's data-logging applications need to safely store huge amounts of data. As a review, data logging is where you capture and store data, then access the data at a later date for review and analysis. Examples of different types of data include temperature, dew point, voltage, current, water pressure, shock and acceleration, sound levels, motor speed RPM--the list is extensive.
Dataloggers fall into two categories: stand alone and embedded. Stand-alone dataloggers are typically external boxes that receive data via external sensors, cables, or wireless RF signals. A familiar example are those boxes you see on the side of the road that count cars as they drive over rubber cables that contain pressure sensors. When the car counting project is completed, the external box is taken back to the office and the data is transferred to a computer for analysis.
Other examples of stand-alone dataloggers include wind-velocity meters; strain-gauge measurement for things like highway bridges; multiparameter measurement of temperature, humidity, pressure, and other environmental parameters; and devices that measure temperature just like those antiquated analog strip-chart recorders, except they do so digitally and enable you to see the color strip chart on your PC, as shown in Figure 1.
Embedded dataloggers, on the other hand, are designed and built into a larger piece of equipment and are a permanent part of that system. These dataloggers typically receive data from wires or cables within the equipment. Examples of embedded dataloggers include remote weather stations, lab equipment like gas chromatographs, motor control, medical equipment like CT scanners (shown in Figure 1b), and so on.
Some of these applications can still use conventional hard disk drives, but many others now demand a flash memory IC-based 100% solid-state solution because of their data-capture speed, physical size, weight, power requirements, and/or hostile environment specs such as vibration, physical shock, and extreme temperature.
These flash-based nonvolatile subsystems are expected to proliferate as flash densities grow and their price points drop. However, in memory subsystems where flash is the only nonvolatile memory, several shortcomings still need to be resolved. These include:
• The risk of losing valuable data during a sudden and unexpected power failure.
• The inability to support extremely high data rates.
• The risk of unplanned memory cell "wear out" due to excessive write operations to the flash memory cells, a fundamental limitation imposed by its underlying process technology.