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.
Among the most important and pioneering innovations in history are devices, techniques, and mediums that have been devised to record and playback sights, sounds, actions, and other information. Many of these innovations have led to the rise and growth of the media and entertainment industries, and also the personal and consumer electronics industries.
For example, among the most notable inventions are Thomas Alva Edison""s phonograph and record with which Edison recorded and played his first recording xe2x80x9cMary Had a Little Lamb.xe2x80x9d Other achievements in this field are the audio tape recorder, cassette tape recorder, motion picture, talking motion picture (xe2x80x9ctalkiesxe2x80x9d), video cassette recorder (VCR), compact disc (CD and CD-ROM), video disc, digital video disc (DVD), and many, many more of such innovations. In the present day, full-length motion pictures with stereo sound may be contained on a single optical disk.
Although these technologies have met with substantial success, there is a continuing desire to improve on the techniques, devices, mediums used to record information. For example, there is a need to provide techniques that provide dense storage of information. Denser storage facilitates storing information in a compact area, and provides a relatively long recording time.
There is a need to provide reliable and robust techniques. The stored reproduction should be a faithful reproduction of the original information. Despite repeated use, the stored reproduction should retain its original form, and also not degrade over time. Furthermore, the techniques should be compatible with and interface easily with present and emerging technologies in electronics and with devices facilitating electronic commerce (such as the Internet and World Wide Web).
Integrated circuit technology has been used to implement many electronic devices including computers, video recorders, digital cameras, microprocessors, DRAMs, SRAMs, Flash memory, and many others. As integrated technology continues to improve, it becomes practical to use this technology to record and playback sights, sounds, actions, and other information.
Data has typically been stored within integrated circuits using a digital or binary format. For applications where the input is analog, however, this requires conversion of signals to digital format, generally by an analog-to-digital (A/D) converter or similar means. And playback of analog signal from a digital storage format may require a digital-to-analog (D/A) converter or similar means. As can be appreciated, these conversions add complexity and extra expense to the entire procedure. Further, a conversion of the signal to digital form quantizes the signal and will lead to quantization noise in the reproduced signal.
Information such as sounds and voices, stereo and multichannel sounds, pictures, video, and others requires many bits of data storage. Storage of data in digital format may be inefficient because one bit (i.e., two different levels) of data is stored in a single memory cell. Further, it may be desirable to store an input signal using a sampling rate the user selects.
Therefore, techniques are needed for compactly storing (and retrieving) analog and digital information including sights, sounds, and actions using integrated circuit technology.
The present invention provides techniques for the storage of information in a medium such as the memory cells of an integrated circuit, and also retrieval of information from the medium. In a particular embodiment, the present invention provides an integrated circuit with nonvolatile memory cells capable of multilevel or analog voltage level storage. The integrated circuit may store or record analog or digital information, or both.
An input signal or other data to be stored in the integrated circuit may be sampled at various sampling rates that are user selectable or user controllable. The sampling rate or sampling frequency may also be dynamically changed while operating the integrated circuit to allow a user to optimize for maximum recording duration or improved recording sound quality, as desired. This sampling frequency may be changed by configuring the integrated circuit. Some of the techniques of the present invention include a series of commands to the integrated circuit (e.g., by way of serial bits or an SPI interface to the integrated circuit); configuring memory cells, registers, combinatorial or sequential logic, or logic gates within the integrated circuit; or many other techniques to permit a user to select a sampling frequency and store the user""s selection on the integrated circuit. This aspect of the present invention permits changing the sampling frequency while the integrated circuit is operating or resident on a system board, without the need to change components external to the integrated circuit (e.g., without the need of changing an external resistor). This feature of the present invention provides greater flexibility in the operation of the integrated circuit.
A plurality of digital bits may be stored in a single multilevel memory cell. Since more than one bit is stored in a memory cell, techniques of the present invention permit denser and more compact storage of digital data.
Further, real world information such as in the form of voices, sounds, images, videos, or actions, and combinations of these, may be converted to electrical signal equivalents using a transducer or other similar device. The resulting analog signal may be stored using the techniques of the present invention directly in the analog memory cells of the integrated circuit. The analog data may be stored without the need for an analog-to-digital (A/D) conversion. And, the present invention also provides techniques for playback or re-creation of the original signal from the stored data. The analog data may be retrieved without the need for a digital-to-analog (D/A) conversion.
In a specific embodiment, a technique of storing data in the integrated circuit includes filtering the input signal and sampling the input signal to obtain data samples. Each data sample is stored or programmed in a memory cell. The sampling rate may be user-selected to allow flexibility in the storage of information. For example, a slower sampling rate may be selected to obtain a lower quality copy of the original signal, but also permits storage of a longer duration of the original signal. On the other hand, if desirable, the sampling rate can be increased to obtain a greater fidelity reproduction, or to store a higher frequency analog signal. The signal path for the analog signal within the integrated signal may also be fully differential to allow for storage of a more precise copy of the original signal.
The data sample is programmed into a memory cell, for example, by adjusting the threshold voltage of a floating gate transistor such as a Flash or EEPROM transistor. The programming technique may use high voltages and level shifting circuitry. The data sample will be level shifted into a voltage range to facilitate programming of the memory cell. For an embodiment of the present invention, the level shifter circuitry is trimmable to allow for adjustments in the output voltage.
A technique of retrieving data stored in the memory cells of the present invention is an inverse of the storage technique. A voltage ramp circuit and sense amplifier is be used to evaluate and determine the threshold voltage of a memory cell. This threshold voltage is then shifted back to the voltage range of the original signal for playback. By playing back the level-shifted threshold voltages for a plurality of memory cells at the original sampling rate, the original signal is re-created.
An analog or digital signal can be stored in an integrated circuit using the techniques of the present invention. Information is more densely stored in an analog or multilevel memory cell. A/D and D/A conversion circuitry is not required, which saves board space and integrated circuit area. When data is stored in digital form, digital compression is used to obtain denser storage. However, because these digital compression techniques (e.g., lossy compression) do not allow an accurate reproduction of the original, there can be artifacts in the playback signal that are not present when stored in analog form. Thus, storing the data in analog form permits greater fidelity in playback, especially without the artifacts due to digital compression.
If even more compact storage of data is desirable, however, the techniques of the present invention can be combined with analog or digital compression techniques to provide for even more storage of information. Digital compression techniques can be used with the multilevel storage scheme of the present invention to provide even denser storage. For example, MP3 format data can be stored using multilevel memory cells of the present invention. MP3 format refers to digitally compressed data stored in an MPEG 1 layer 3 format. MP3 is a popular format for storing and transferring audio and music files, especially over the Internet.
In a specific embodiment of the present invention, the present invention provides a fully integrated single-chip recording and playback device with a long recording duration. Analog signals are directly stored in the integrated circuit without the need for an analog-to-digital conversion. In a specific application of voice recording, it is desirable to have good sound quality in the reproduced signal. A flexible architecture is provided, so recording quality and recording duration may be adjusted as a user desires. The integrated recording device also retains its recorded information indefinitely, even when power is removed from the integrated circuit. The form factor of the present invention is compact and can be used in many applications where other devices or techniques are not suitable.
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 figures.