NvSRAM
Encyclopedia
nvSRAM is a type of non-volatile
computer memory. It is similar in operation to SRAMs. The current market for non volatile memory is dominated by BBSRAMs, or Battery Backed Static Random Access Memory. However, BBSRAMs are slow and suffer from ROHS
compliance issues. nvSRAMs provide 20ns or lesser access times.
nvSRAM is one of the advanced non-volatile memory NVRAM
technologies that is fast replacing the BBSRAMs, especially for applications that need battery free solutions and long term retention at SRAM speeds.
nvSRAM is available from 16k densities up to 8M densities from both Simtek Corporation
and Cypress Semiconductor
. There are other nvSRAM products from Maxim which are essentially BBSRAMs. They have a lithium battery
built into the SRAM package. It is an efficient replacement for BBSRAM, EPROM
or EEPROM
. It is faster than EPROM and EEPROM solutions. It is better than BBSRAM solution because there is no ROHS issue associated with this type of memory. No external battery is used.
signal is an optional signal that does not have to be used. However, on the inside, there is a lot more going on and the nvSRAM is capable of doing more than a standard SRAM. With nvSRAM there are four operations compared to two in SRAM read/write
. nvSRAM can read, write, store and recall. The additional operations center around the non volatile part of the nvSRAM.
When reading and writing the nvSRAM acts no differently than a standard async SRAM. The attached processor or controller sees a 8-bit
SRAM interface and nothing else. The STORE operation is when the data that is in the SRAM array is stored in the non volatile part. Cypress and Simtek nvSRAM has three ways of storing data in the non-volatile area. They are:
Autostore happens automatically when the data main voltage source
drops below the devices operating voltage. When this occurs, the power control is switched from Vcc
to the capacitor
. The capacitor will power the chip for enough duration to store the SRAM contents into the non volatile part. The HSB pin can externally initiate the store operation. This is called hardware store. Software store is initiated by a certain sequence of operations. When the defined operations are done in sequence the software store is initiated.
terminals/smart terminals are now able to approve payment transactions
without having to obtain approval from a remote server
. Because secure data resides in the terminal, a lot of time could be saved in terms of the over-the-air verification which is slow as well as intrusion prone.
Motor vehicle
crash boxes
are another area where nvSRAMs could be employed effectively. The vehicle state data at the time of the crash can go a long way in validating the claims and finding the reason of the crash. This has huge financial implications in the insurance
industry, and the concept of having crash boxes in passenger/commercial vehicle
s could become a defacto standard in near future. nvSRAMs with their fast read/write
capabilities is a good fit for this application.
Similar critical applications such as medical equipment
and high end servers can use nvSRAMs to store their data. In case of external power failure
, or unforeseen calamities, nvSRAM can hold the data without external intervention (autostore feature). Hence it would provide the flexibility of an EEPROM but at SRAM speeds.
Applications in environments where field service is not possible/costly such as data loggers spread across geographies, routers, equipment in in hospitable conditions can use nvSRAMs, because nvSRAM does not use batteries
, which have a risk of exploding/releasing harmful chemicals in harsh environments.
In short, nvSRAMs are suited for applications that need to store critical data
, but no field service.
Non-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
computer memory. It is similar in operation to SRAMs. The current market for non volatile memory is dominated by BBSRAMs, or Battery Backed Static Random Access Memory. However, BBSRAMs are slow and suffer from ROHS
Restriction of Hazardous Substances Directive
The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state...
compliance issues. nvSRAMs provide 20ns or lesser access times.
nvSRAM is one of the advanced non-volatile memory NVRAM
NVRAM
Non-volatile random-access memory is random-access memory that retains its information when power is turned off, which is described technically as being non-volatile...
technologies that is fast replacing the BBSRAMs, especially for applications that need battery free solutions and long term retention at SRAM speeds.
nvSRAM is available from 16k densities up to 8M densities from both Simtek Corporation
Simtek Corporation
Simtek Corporation, headquartered in Colorado Springs, CO, was an early leader in the development of SONOS memory technology which it used in its nvSRAM product line which featured a SONOS Flash memory coupled with an SRAM shadow memory to achieve both speed and non-volatility...
and Cypress Semiconductor
Cypress Semiconductor
Cypress Semiconductor Corporation is a Silicon Valley-based semiconductor design and manufacturing company founded by T. J. Rodgers and others from Advanced Micro Devices. It was formed in 1982 with backing by Sevin Rosen and went public in 1986. The company initially focused on the design and...
. There are other nvSRAM products from Maxim which are essentially BBSRAMs. They have a lithium battery
Lithium battery
Lithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...
built into the SRAM package. It is an efficient replacement for BBSRAM, EPROM
EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...
or EEPROM
EEPROM
EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...
. It is faster than EPROM and EEPROM solutions. It is better than BBSRAM solution because there is no ROHS issue associated with this type of memory. No external battery is used.
Description
This is the basic block diagram of a nvSRAM. Externally nvSRAM looks like a standard SRAM. The HSBHSB
HSB may refer to:* Hue, saturation, brightness, a variation of the HSV color space* a beer made by Gales Brewery* The annual Hardly Strictly Bluegrass festival in San Francisco, California* acronym for the Head Start Bureau...
signal is an optional signal that does not have to be used. However, on the inside, there is a lot more going on and the nvSRAM is capable of doing more than a standard SRAM. With nvSRAM there are four operations compared to two in SRAM read/write
Read-write memory
Read-write memory is a type of computer memory that may be relatively easily written to as well as read from . The term RAM is often used to describe writable memory. RAM actually referring to memory that can be accessed at any "location"....
. nvSRAM can read, write, store and recall. The additional operations center around the non volatile part of the nvSRAM.
When reading and writing the nvSRAM acts no differently than a standard async SRAM. The attached processor or controller sees a 8-bit
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
SRAM interface and nothing else. The STORE operation is when the data that is in the SRAM array is stored in the non volatile part. Cypress and Simtek nvSRAM has three ways of storing data in the non-volatile area. They are:
- Autostore,
- Hardware store,
- Software store.
Autostore happens automatically when the data main voltage source
Voltage source
In electric circuit theory, an ideal voltage source is a circuit element where the voltage across it is independent of the current through it. A voltage source is the dual of a current source. In analysis, a voltage source supplies a constant DC or AC potential between its terminals for any current...
drops below the devices operating voltage. When this occurs, the power control is switched from Vcc
IC power supply pin
Almost all integrated circuits have at least two pins that connect to the power rails of the circuit in which they are installed. These are known as the IC's power supply pins...
to the capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
. The capacitor will power the chip for enough duration to store the SRAM contents into the non volatile part. The HSB pin can externally initiate the store operation. This is called hardware store. Software store is initiated by a certain sequence of operations. When the defined operations are done in sequence the software store is initiated.
Applications
Data logging is one main area where nvSRAMs are needed. POSPoint of sale
Point of sale or checkout is the location where a transaction occurs...
terminals/smart terminals are now able to approve payment transactions
Financial transaction
A financial transaction is an event or condition under the contract between a buyer and a seller to exchange an asset for payment. It involves a change in the status of the finances of two or more businesses or individuals.-History:...
without having to obtain approval from a remote server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
. Because secure data resides in the terminal, a lot of time could be saved in terms of the over-the-air verification which is slow as well as intrusion prone.
Motor vehicle
Motor vehicle
A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...
crash boxes
Black Box (transportation)
The term black box is a placeholder name used casually to refer to a collection of several different recording devices used in transportation: the flight recorders in aircraft, the event recorder in railway locomotives, the event data recorder in automobiles, message case in ships, and other...
are another area where nvSRAMs could be employed effectively. The vehicle state data at the time of the crash can go a long way in validating the claims and finding the reason of the crash. This has huge financial implications in the insurance
Insurance
In law and economics, insurance is a form of risk management primarily used to hedge against the risk of a contingent, uncertain loss. Insurance is defined as the equitable transfer of the risk of a loss, from one entity to another, in exchange for payment. An insurer is a company selling the...
industry, and the concept of having crash boxes in passenger/commercial vehicle
Commercial vehicle
A commercial vehicle is a type of motor vehicle that may be used for transporting goods or passengers. The European Union defines "commercial motor vehicle" as any motorised road vehicle, which by its type of construction and equipment is designed for, and capable of transporting, whether for...
s could become a defacto standard in near future. nvSRAMs with their fast read/write
Read-write memory
Read-write memory is a type of computer memory that may be relatively easily written to as well as read from . The term RAM is often used to describe writable memory. RAM actually referring to memory that can be accessed at any "location"....
capabilities is a good fit for this application.
Similar critical applications such as medical equipment
Medical equipment
Medical equipment is designed to aid in the diagnosis, monitoring or treatment of medical conditions.-Types:There are several basic types:* Diagnostic equipment includes medical imaging machines, used to aid in diagnosis...
and high end servers can use nvSRAMs to store their data. In case of external power failure
Power outage
A power outage is a short- or long-term loss of the electric power to an area.There are many causes of power failures in an electricity network...
, or unforeseen calamities, nvSRAM can hold the data without external intervention (autostore feature). Hence it would provide the flexibility of an EEPROM but at SRAM speeds.
Applications in environments where field service is not possible/costly such as data loggers spread across geographies, routers, equipment in in hospitable conditions can use nvSRAMs, because nvSRAM does not use batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, which have a risk of exploding/releasing harmful chemicals in harsh environments.
In short, nvSRAMs are suited for applications that need to store critical data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
, but no field service.
Comparisons with other types of memories
| nvSRAM | BBSRAM | FRAM Ferroelectric RAM Ferroelectric RAM is a random-access memory similar in construction to DRAM but uses a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile memory technologies that offer the same functionality as Flash memory... |
MRAM | |
|---|---|---|---|---|
| Technique | Has non-volatile Non-volatile memory Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer... elements along with high performance SRAM |
Has a lithium Lithium Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly... energy source for power when external power Power supply A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy... is off |
Has a ferro electric crystal between two electrode Electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit... s to form a capacitor Capacitor A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated... . The moment of atoms on application of electric field is used to store data |
Similar to FRAM, but the atoms align themselves in the direction of an external magnetic force Magnetic field A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;... . This effect is used to store data. |
| Data retention | 20 yrs Year A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic.... |
7 yrs, dependent on battery and ambient temperature | 10 yrs | 20 yrs |
| Endurance | Unlimited | Limited | Unlimited | |
| Store mechanism | Autostore initiated when Vcc IC power supply pin Almost all integrated circuits have at least two pins that connect to the power rails of the circuit in which they are installed. These are known as the IC's power supply pins... power down is detected |
Chip enable must be maintained at high logic to prevent inadvertent read/writes Read-write memory Read-write memory is a type of computer memory that may be relatively easily written to as well as read from . The term RAM is often used to describe writable memory. RAM actually referring to memory that can be accessed at any "location".... . |
Static operation. Data is stored in the NV Non-volatile memory Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer... part only |
|
| Power up data restore | Non volatile data is made available automatically in the SRAM | SRAM will switch from battery to Vcc | ||
| Substitution with SRAM | nvSRAM can be substituted for SRAM with minor board modification to add external capacitor | Provision for battery Battery (electricity) An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power... necessitates board redesign to accommodate bigger size for the battery |
Some parts are pin-to-pin compatible with existing SRAMs | Pin-to-pin compatible with existing SRAMs |
| Soldering | Standard SMT Surface-mount technology Surface mount technology is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards . An electronic device so made is called a surface mount device... used |
Reflow solder Reflow soldering Reflow soldering is a process in which a solder paste is used to temporarily attach one or several electrical components to their contact pads, after which the entire assembly is subjected to controlled heat, which melts the solder, permanently connecting the joint... cannot be done as batteries may explode |
Standard SMT used | |
| Speed (best) | 15 – 45 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... |
70 – 100 ns | 55 ns | 35 ns |