Electrical audio signal processing systems and devices – Monitoring/measuring of audio devices
Reexamination Certificate
1998-12-20
2001-08-21
Psitos, Aristotelis M. (Department: 2651)
Electrical audio signal processing systems and devices
Monitoring/measuring of audio devices
C369S053120, C360S031000
Reexamination Certificate
active
06278784
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to testing and troubleshooting of digital disc players and data storage drives. More particularly, it relates to a novel apparatus and method for detecting and recording random and/or intermittent errors made during play by digital disc players or the like, such as those that read or play audio compact discs, CD-ROM discs, or digital versatile discs (DVD). The invention can also be used to detect and record intermittent errors in analog or digital signal paths, as discussed below.
For simplicity of explanation in this disclosure, and merely by way of example, some discussion here addresses testing of players that use various conventional rotating disc media encoded with the CD (Compact Disc or Red Book) format, such as CD-DA (Compact Disc Digital Audio), or DVD (Digital Versatile Disc) formats, where pulse code modulated (PCM) audio, video, or other data is encoded, with error correction and other features, using long strings of physical pits written helically on the reflective surface of a polycarbonate disc. However, the invention shall apply equally well to other present and future formats, such as DVD (digital versatile disc) formats that may use Direct Stream Digital (DSD) encoded data; or future formats where rotating discs or other digital media are played. This would include future solid state media such as photorefractive volume holographic storage (PVHS), where the storage medium is not physically rotated, and where data is accessed by directing a laser beam to various physical portions of a crystal or other solid.
Digital disc systems are known for unprecedented fault tolerance, accuracy and reproducibility. Properly functioning digital disc player systems are generally impervious to noise and major output signal defects due to robust error correction and modulation schemes. When problems with digital disc players do occur, however, their appearance is often intermittent and difficult to discern. Although there tends to be general agreement Concerning format specifications for digital discs, manufacturers of digital disc players have freedom to employ differing designs in their players. This results in a wide variety of player designs, with differing individual error and failure modes, which compounds problem diagnosis.
Aside from problems arising from physical impact and damaged or soiled disc player media, there are component or system problems that manifest themselves in subtle ways. Some of these problems cause random or intermittent errors which are extremely troublesome for CD player repair technicians to locate and diagnose. Time spent on signal or output monitoring in order to make a diagnosis in these cases often can far exceed time spent on repair or replacement of the failing individual components.
Troubleshooting digital disc players is also difficult and, time-consuming because of their complexity. Error correction, synchronization and modulation require electronic and logic circuits; tracking and focusing require optical and electro-mechanical servo systems.
Many intermittent-type failure modes result, in part from: [1] temperature-induced stresses; [2] specific conditions such as wear and accumulation of debris and dirt on mechanical components; [3] factory assembly errors that result in momentary malfunctions; [4] environmental factors such as humidity and dust; and [5] systemic factors resulting from the use of specific assemblies or structures, such as the use of arm-mounted pickups that move in an arc or tangentially across the surface of the storage medium, cable stresses and fatigue, bearing failures, and other electrical, electromechanical, or mechanical defects.
These all present challenges for diagnosis, repair, testing and service of digital disc players. Often, when a digital disc player fails intermittently, it must be tested at length prior to and after repair, in an effort to establish which components or systems are at fault, as well as to provide confirmation that repairs are properly effected and will solve the problem where it originates.
Error correction, synchronization, and modulation all play roles in determining actual signal output. With errors in the pickup signal corrected, compensated or masked by the playback systems in use, the character of digital disc player problems or malfunctions becomes even more intermittent and subtle.
Digital Disc Formats and Player Design
Digital disc formats and players allow high density information storage with nearly error-free retrieval at high bit: rates, in part by use of error correction and modulation schemes. Audio Compact Discs, for example, store a digitized stereo audio signal comprised of two 16 bit words at a sampling frequency of 44.1 kHz. This corresponds to about 1.41 million bits per second (Mbps). Additional required data overhead in the form of formatting, modulation, and notably error correction and synchronization, triple the data rate required to about 4.32 million bits per second (Mbps). The corresponding bit rates for DVD players are substantially higher.
Typically, this information is physically stored on the digital disc in the form of pits or depressions that are formed or impressed into a plastic or deformable substrate. These pits are of various lengths, and are arranged in a helical spiral, starting from the inner radius of the disc. For Compact Discs read by near-infrared AlGaAs lasers with typical wavelength of 780 nm, each pit is about 0.6 microns wide, 0.11 microns deep, and with lengths varying from about 0.8 to 3.6 microns. The helical track pitch is typically 1.6 microns. A typical audio Compact Disc following the CD-DA format may contain 2-3 billion such pits, forming a trail or track on the disc “land” of over 5 km (3 miles) length. This typically yields up to 783 million bytes of usable information, allowing for a typical maximum disc play time of 74-80 minutes. Recent DVD disc players use lasers with a typical wavelengths of 650 and 635 nm (red), and use a higher numerical aperture (NA=0.60) lens. This allows focusing on pits formed on DVD discs having lengths down to 0.4 microns minimum, using a track pitch of only 0.74 microns. Future formats may use smaller geometries.
Light is used to read the pits from the underside (as bumps or protrusions). The underside of the pitted surface is treated to reflect a laser beam, usually via metallization using aluminum, copper or silver by means of vapor deposition, magnetron sputtering, or non-electrolytic wet silvering.
To play the disc, a laser scanning spot is trained upon, and maintained in focus and alignment upon, the underside of the helical pit trail, while the disc is rotated about its central axis at regulated constant linear velocity, typically 1.2 m/s for audio CDs. Data is read via changes in the intensity of reflected laser light.
Refractive properties of the disc, typically a polycarbonate substrate, are arranged so that a relatively large beam spot is internally focused down to a much smaller spot on the plane where the digital disc pits reside. With Compact Discs, for example, an 0.8 mm diameter laser beam impinging upon the plastic disc outer surface is internally focused down to a 1.0 micron scanning spot on the internal data (pit) surface. This allows that the image size of any surface contamination on the surface of the disc (e.g., dust) is small and out of focus. The result is that in practice, obstructions to the laser beam of less than about 0.5 mm length cause no error in the raw data or pickup signal.
The depth of the pits impressed or formed into a typical digital disc is set so that when the laser scanning spot hits the underside of the pits, destructive interference reduces greatly the intensity of laser light reflected. During play, this forms an intensity-modulated reflected beam which is transduced by a photodiode or photodiode array, as known in the art. Abrupt changes in the state of the photodiode or photo diode array are encoded into binary electrical signals.
By a common
Elting Mark J.
Psitos Aristotelis M.
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