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    • 4. 发明授权
    • Data retrieval system and method within a constant angular velocity
CD-ROM
    • 恒定角速度CD-ROM内的数据检索系统和方法
    • US5703850A
    • 1997-12-30
    • US666776
    • 1996-06-18
    • Takeo Wada
    • Takeo Wada
    • G11B19/247G11B19/28G11B20/10G11B20/14G11B5/09
    • G11B19/28G11B19/247G11B20/10G11B20/1403
    • A method and system retrieving data stored on a compact disk read only memory (CD-ROM) device using the constant angular velocity (CAV) reading technique. Unlike the constant linear acceleration (CLA) reading technique, in the CAV reading technique the data retrieval rates of the CD-ROM read head vary depending on the radius of the annular recording track that is being read. Data rates can be as much as 2.5.times. faster for the outer recording tracks compared to the inner recording tracks. The novel system utilizes a narrow capture band phase lock loop circuit in conjunction with a microcontroller which controls the center frequency supplied to the phase lock loop circuit. The microcontroller adjusts the center frequency of the phase lock loop circuit depending on the track (e.g., radius) position of the read head of the CD-ROM device. With the center frequency adjusted close to the data rate of the current track, the phase lock loop circuit needs only a narrow capture band to accurately retrieve the read reference clock from the current track. In one embodiment, the microcontroller is aware of the read head position because it controls read head movement. A microcontroller controlled programmable oscillator (e.g., synthesizer) is used in one embodiment of the novel system to generate the required center frequencies. Direct computation or a look-up table based on the read head position can be used by the microcontroller to determine the required center frequencies. A decoder is supplied with the read reference clock for data decoding.
    • 一种使用恒定角速度(CAV)读取技术检索存储在光盘只读存储器(CD-ROM)设备上的数据的方法和系统。 与恒定线性加速(CLA)读取技术不同,在CAV读取技术中,CD-ROM读取头的数据检索速率根据正在读取的环形记录轨道的半径而变化。 与内部记录轨道相比,外部记录轨道的数据速率可以高出2.5倍。 该新颖系统与控制提供给锁相环电路的中心频率的微控制器结合使用窄捕获带锁相环电路。 微控制器根据CD-ROM设备的读取头的轨迹(例如,半径)位置来调节锁相环电路的中心频率。 当中心频率调整为接近当前音轨的数据速率时,锁相环电路仅需要窄的捕获频带,以便从当前音轨精确检索读取的参考时钟。 在一个实施例中,微控制器知道读头的位置,因为它控制读头的运动。 在新颖系统的一个实施例中使用微控制器控制的可编程振荡器(例如,合成器)来产生所需的中心频率。 微控制器可以使用基于读取头位置的直接计算或查找表来确定所需的中心频率。 解码器被提供有用于数据解码的读取参考时钟。