|Memory card: Compact Flash, Memory Stick, SD card|
|Thursday, 07 December 2006|
A memory card contains a rewritable nonvolatile memory, which does not lose information saved therein even if the power supply is turned off, along with a controller that controls operation of the memory cell array and interfaces with a host to which the card connected. Among nonvolatile semiconductor memory device in which data can be electrically erased/written, in a block erasable flash memory, an electric charge of a floating gate of a memory cell transistor is changed by an erase/write operation to change a threshold voltage, and the data is stored. Memory cards typically comprise multiple integrated circuit devices or semiconductor dies. The dies are interconnected using a circuit board substrate which adds to the weight, thickness, stiffness and complexity of the card. A memory card typically includes a flat framework made of plastic material for holding a circuit board and the circuit elements thereof. For the memory card to be thin and rigid as required, metal covers are further mounted onto upper and lower surfaces of the plastic framework. Memory cards also include electrical contacts for providing an external interface to an insertion point or socket. These electrical contacts are typically disposed on the backside of the circuit board substrate, with the electrical connection to the dies being provided by vias which extend through the circuit board substrate. Numerous memory standards can be used in memory cards, including electrically erasable programmable read only memory (EEPROM), non-volatile random access memory (NVRAM), and other non-volatile or volatile memory types, such as synchronous dynamic random-access-memory (SDRAM), with battery backup. An electrically erasable programmable read only memory (EEPROM) is a memory device that has been widely used in information electronic products. Data can be directly written into blank EEPROM sectors in the same way as for magnetic or optical discs. However, when EEPROM sectors already contain data, this data has to be deleted, returning the sectors to a blank state, before new data can be written into the sectors. Consequently, the semiconductor memory card contains a specialized internal control circuit for realizing memory management using erasable blocks as access units. Status control of erasable blocks, and reading and writing of data to/from erasable blocks, is managed by this control circuit.
Flash memory is a special version of an EEPROM that allows multiple memory locations to be erased or written in one programming operation, instead of having to be removed and reprogrammed in a special device. The semiconductor memory typically comprises an array of memory cells, address decoding circuitry for selecting one, or a group, of the memory cells for reading or writing data, sensing circuitry for detecting the digital state of the selected memory cell or memory cells, and input/output lines to receive the sensed data and convey that information for eventual output from the semiconductor memory. A flash memory card is a nonvolatile memory device with a compact housing that does not require a power source in order to retain its memory contents. A typical flash memory card stores charge on a floating gate to represent a first logic state of the binary state system, while the lack of stored charge represents a second logic state of the binary state system. The flash memory serving as a loader of data storage really brings extremely convenient for the information industry, and it is beneficial for the main memory that it is unnecessary to offer a huge space while a single independent or temporary data is saved. Meanwhile, the specific data can be saved and managed well through a single memory. Small flash memory cards have been designed that have a connector that can plug into a specialized reader. Through external contact terminals, memory cards store information using internally disposed memories thereof, and forward information signals to a card reading device, with the information signals further accepted by a computer host. Flash memory cards are formed in card shapes in which memory chips are sealed in card type outer shells. Examples of the flash memory cards include ones meeting various standards such as an SD card, a multimedia card, a smartmedia card, a compact flash (CF) card, and a memory stick. Flash memory cards are generally used in the field of information appliance by virtue of the convenience of data storage and transmission. The characteristics of plug-and-play and carry easily make silicon disks become popular data storage media in the market. The flash memory cards were originally popular only in the field of digital cameras, and most of them were directly connected to a computer via a USB data transmission line. The most important function of the flash memory card at that time was to store photos taken with a digital camera. Nowadays flash memory cards are widely incorporated into various portable electronics.
Memory cards in various formats exist in the market, and they are continuously developed in different formats. Memory cards can be classified as large memory cards and small memory cards based on size. Large memory cards comprise MMC (MultiMedia card), CF (CompactFlash card), SD (Secure Digital), XD (xD-piture card), SM (Smart Media), and MS (Memory Stick) available from SONY Corporation. Small memory cards comprise miniSD, microSD (T-Flash), RSMMC, MMC micro, MS Duo, and Memory Stick Micro. MMC, CF, and SD cards not only have large market shares but also are widely used as main memory cards in digital cameras, MP3 players, and other multimedia devices. The specifications of SD and MMC are complied with the miniaturization of Smart Phone. Thus, SD and MMC are taken as standard storage devices by major mobile phone manufacturers such as Samsung Electronics, Nokia, and Motorola. Small memory cards are advantageous for being compact, lightweight, energy saving, durable, and rewritable. Thus, small memory cards are widely mounted in various portable electronic products including personal digital assistant, digital camera, digital music player, and smart phone. Further, small memory cards have certain advantages and relatively large market shares because they concentrate on markets different from that of large memory cards. Among these removable storage devices, the multimedia card, the SD memory card and the memory stick all have copyright protection functions. One of the most common memory cards in the market is SD memory card that has a conducting interface with nine contact pins at the bottom of the front end thereof. Another common memory card is MMC memory card that has a conducting interface with seven contact pins. Both SD and MMC cards are thin and the area they occupy is about that of a large postage stamp. The difference between the SD card and the MMC card is the number of contact pins and the thickness so that a common slot socket of the read and write apparatus is enough for both of the cards. Secured Digital (SD) cards are hot-swappable, allowing the user to easily insert and remove SD cards without rebooting or cycling power. A SD memory card, which has small volume, fast accessing ability, and good applicability to digital cameras, has potential to dominate the small-sized memory card market. Since the SD cards are small, durable, and removable, data files can easily be transported among electronic devices by being copied to an SD card. SD cards are not limited to flash-memory cards, but other applications such as communications transceivers can be implemented as SD cards. Flash memory is typically implemented in the form of compact flash (CF) cards which comprise small, removable mass storage devices. CF cards and other compact flash storage products are designed with flash technology, which is a non-volatile storage solution not requiring a battery to retain data indefinitely. CF storage products are generally considered to be five to ten times more rugged and reliable than disk drives including those found in personal computers, and typically consume only five percent of the power required by small disk drives. The storage capacity of an XD card can be expanded to several BGB, meeting user's requirement for image processing.
One of the advantages of the memory card is its interchangeability in being utilized in different types of electronic devices. For example, a digital camera configured to receive the MultiMedia Card may be configured to store digital photographs. That same card may then be inserted into a computer to download the digital photographs, or such memory card may be utilized in a cell phone for one function and then transferred to another electronic device such as a personal data assistant for a second function. Thus, the success of the memory card in the market has been largely due to the interchangeability of the memory card from one electronic device to another. However, there is no uniform standard or specification presently in the art of memory cards in the whole world presently. Different brands of electronic devices may still utilize particular types of memory cards, each such electronic device including a memory card socket configured to receive a corresponding memory card with corresponding dimensions. CF cards (Compact Flash cards), SM cards (Smart Media cards), MMC cards (MultiMedia cards), MS cards (Memory Stick cards) and SD cards (Secure Digital cards) not only are multifactorial, but also have their respective predominance in the markets. Each of the different memory cards typically has a unique connector, which defines the electrical and mechanical interfaces of the card. Moreover, each different memory card generally requires a specialized adapter or reader for use with a host computing device. The adapter or reader includes a specialized interface that conforms to that of the memory card, and an interface that can be accepted by a host computer. The CF and PC memory cards are of pin-contact memory cards, while the SM and MS memory cards are of surface-contact memory cards. The pin-contact memory card has a contact section at where a 50-hole or a 68-hole female connector is provided. The pin-contact memory card is designed to plug in a machine at a memory card slot thereof. The surface-contact memory card has a contact section provided at a front end of one side thereof. The contact section includes a plurality of spaced contact areas. The surface-contact memory card is designed to plug in a machine at a memory card slot thereof. A head in the memory card slot for reading data is provided at a portion contacting with the plugged memory card with a plurality of elastic contact plates corresponding to the contact areas on the memory card.
In general, a memory card is used while being connected to a host system which processes information. The memory card is connected to the host system such that the host system can store, read, or overwrite data in the memory card. Many consumer electronics are now constructed to generate and/or utilize digital data in increasingly large quantities. Portable digital cameras for still and/or moving pictures generate large amounts of digital data representing images. Each digital image may require up to several megabytes (MB) of data storage, and such storage must be available in the camera. To provide for this type of data storage application, the storage memory should be relatively low in cost for sufficient capacities of around 100 MB to one gigabyte (GB). The storage memory should also be low in power consumption and have relatively rugged physical characteristics to cope with the portable battery powered operating environment. For accessing the flash memory cards, the digital electronic products are equipped with electrical connectors adapted to corresponding flash memory card. Most of the electrical connectors have a foolproof design to prevent the failure of the flash memory cards and the digital electronic products resulted from the wrong insert direction. Some electrical connectors have a mechanism for rejecting the flash memory cards. The memory card connector often is mounted on a printed circuit board. The memory card writes or reads via the connector and can transmit between electrical appliances, such as a word processor, personal computer, personal data assistant or the like. The connector terminals typically have tail portions for connection to appropriate circuit traces on the printed circuit board. A flash memory card driver is a device to access portable storage memory cards. In order to make card driver products satisfy customers' demands better, some manufacturers add appropriate adapters to those card drivers, thus the card drivers can access multi types of memory cards, expanding their application scopes. The main function of the card reader is to serve as a bridge between the flash memory card and the computer to complete data transmission between them. Via the card reader, a user may browse photos stored on the flash memory card, listen to music, and store files on a computer without being connected to the computer.