Static information storage and retrieval – Analog storage systems
Reexamination Certificate
1999-06-02
2001-03-27
Nelms, David (Department: 2818)
Static information storage and retrieval
Analog storage systems
C365S189030, C365S189011
Reexamination Certificate
active
06208542
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of information storage and retrieval using integrated circuit technology. More specifically, the present invention relates to techniques for storing and retrieving analog or digital data, or both, within an integrated circuit using multilevel nonvolatile cells.
In the real world, information comes in both digital and analog forms. Some examples of analog information include voices, sounds, images, video and electromagnetic radiation. Digital data includes binary information used in computers and electronic systems. There are digital integrated circuit memories such as DRAMs, SRAMs, Flash, and EEPROM memories. There are also analog integrated circuit memories. Some examples of analog integrated circuit memories are described in U.S. Pat. Nos. 5,694,356, 5,680,341, 5,745,409, 5,748,534, 5,748,533, 5,818,757, and U.S. provisional patent application Nos. 60/091,326 and 60/116,760, all incorporated by reference.
Although these types of memory devices have met with substantial success, there is a need for devices that will store both analog and digital information. As an example, in telephony applications, it is desirable to have an answering machine memory chip that can store both voice messages and digital information such as phone numbers. These memory devices should store the analog or digital data directly, without requiring the additional processing time and complexity of, for example, translating analog information into a digital form. Techniques are also needed for an analog and digital memory that will facilitate further miniaturization in electronics for use in such devices as voice recorders, cellular phones, animal- or human-implantable devices, and others.
Therefore, techniques and devices are needed for storing and retrieving analog and digital data using integrated circuit technology.
SUMMARY OF THE INVENTION
The present invention provides techniques to implement an integrated circuit memory for storing digital and analog data. Analog information is provided at an analog input and sampled. Each analog sample is stored in one or more memory cells in analog form. The memory cells of the present invention provide analog or multilevel storage of data. These memory cells may be floating gate memory cells, which are nonvolatile. The sampling frequency can be fixed or user-selectable. Digital data is provided at an digital input and stored into the memory cells of the integrated circuit. The same memory cell used for analog information storage on one occasion may be used for digital information storage on another occasion. Analog data may be retrieved from the memory cells and output at an analog output. Digital information may be received from the memory cells and output at a digital output.
In one embodiment, the invention is a method of storing information in a memory. An analog signal is provided at an analog signal input. A digital data is provided at a digital signal input. The analog signal input is sampled at a sampling frequency. This sampling frequency can be fixed by the design on the integrated circuit or user-selectable. The user can select the sampling frequency by changing an external device to the integrated circuit, such as a resistor or capacitor, or by loading into the device an indication (e.g., a series of bits) of the desired frequency. Samples of the analog signal are stored in an array of memory cells, where a memory cell holds one sample of the analog signal. The digital data is stored in the array of memory cells, wherein a memory cell holds at least one bit of the digital data. Each memory cell may store two, three, four, five, six, seven, eight, or more digital bits of data. The invention provides a consistent scheme for storing both analog and digital data.
In another embodiment, the invention is an integrated circuit including an array of memory cells and a write circuit to store information provided at an analog input and a digital input of the integrated circuit into the memory cells. The information provided at the analog input is in an analog form and at the digital input is in digital form. A multiplexer selectively couples the analog or the digital input to a common write circuit, to convert the input to a precise threshold voltage and store into one memory cell.
A further embodiment of the present invention is an integrated circuit including a plurality of memory cells and a write circuit connected to the memory cells. A read circuit will determine a threshold voltage stored in individual memory cells, and will provide an analog equivalent of the stored threshold voltage at an analog output or will provide a digital equivalent of the stored threshold voltage at a digital output. Individual memory cells are configured using the common write circuit to store a precise threshold voltage level based on the sampled input level. In a specific implementation, the read circuit determines whether a threshold voltage stored in a memory cell is above or below a reference level, and provides to the digital output a first logic level when the stored threshold voltage is below the reference level and a second logic level when the stored threshold voltage is above the reference level.
In a further embodiment, the present invention is an integrated circuit including an array of multilevel memory cells and a write circuit connected to store data in the array of multilevel memory cells. A digital reference generator receives digital data and converts the digital data into an analog equivalent form. The analog equivalent form is provided to the write circuit. In a specific implementation, the digital reference generator includes a bias voltage generator generating a number of bias voltages. The digital reference generator also includes a digital data input circuit to generate the analog equivalent form of the digital data by selecting combinations of the bias voltages.
The invention also includes a method of storing information in a memory including providing an analog signal at an analog signal input and providing digital data at a digital signal input. The analog signal input is sampled at a sampling frequency, where may be user-selectable. Samples of the analog signal are stored in an array of memory cells, where a memory cell holds at least one sample of the analog signal. The digital data is stored in the array of memory cells, where a memory cell holds at least a bit of the digital data. The digital data is stored by first erasing a sector of memory cells and then writing the digital data in the sector of memory cells. A digital value is written in each memory cell of the sector not written with the digital data. This ensures memory cells do not subject to an overerase condition. A sector, sometimes called page, of memory cells may be any number of memory cell (e.g., 3K cells). The memory cells in a sector will usually have a common source line, or erase node, in order to erase the contents of the whole sector of cells together.
In another aspect, the present invention includes the use of an integrated circuit to store both analog signals and digital data in the same analog or multilevel memory cells of the integrated circuit, where the sampling frequency used to sample the analog signals can be user-selectable. The invention includes the use of requiring writing of every memory cell in a sector of an integrated circuit with a value in order to prevent overerase of the memory cells in the sector. The invention also includes the use of a digital reference generator to generate a analog equivalent to a digital quantity to be stored, and storing this analog equivalent into memory cells of an integrated circuit. In a further aspect of the invention, the use of an analog memory integrated circuit as a nonvolatile multilevel digital memory
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the f
Haeberli Andreas M.
So Hock C.
Wang Cheng-Yuan Michael
Werner Carl W.
Wong Leon Sea Jiunn
Le Thong
Nelms David
SanDisk Corporation
Skjerven Morrill & MacPherson LLP
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