Loopback Circuit Self-Testing for Disk Drive Read Channels
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Solution Overview
Problem
Conventional test equipment is impractical for testing complex devices and subsystems in compact and high-speed disk drives due to their shrinking physical dimensions and increasing data transfer rates, making it difficult to verify the functionality of hard disk controllers and read channel devices.
Innovation Solution
A system comprising a hard disk controller module and a read channel device with a loopback circuit that generates independent write and read clocks, allowing for self-testing without external equipment by looping back the write bus to the read bus, using a fixed RC timebase or a recovered channel clock, and disabling clock stretching and rephasing to ensure constant periodicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external test equipment is used to test electronic devices in disk drives, then testing accuracy can be ensured, but the testing becomes increasingly impractical as disk drives shrink in size and increase in speed
Solution Approach 1:
The disk drive system performs self-testing through an internal loopback circuit that allows the read channel device to test the write channel functionality without requiring external test equipment. The system uses its own resources (read bus, write bus, clocks) to conduct comprehensive tests of electronic devices within the compact drive environment
Solution Approach 2:
The read channel device is designed to perform multiple functions: normal data reading operations and self-testing of the write channel through loopback circuitry. This multi-functionality eliminates the need for separate external test equipment while maintaining testing capabilities within the compact drive form factor
2Device complexity
If a single clock is used for both read and write operations, then device complexity is reduced, but testing accuracy deteriorates due to clock stretching and rephasing irregularities
Solution Approach 1:
The clock generation is segmented into separate write clock and read clock paths. The write clock is generated with constant periodicity using a fixed RC timebase, while the read clock can have irregularities due to stretching and rephasing. This segmentation allows each clock to be optimized for its specific function, with the write clock providing stable timing for accurate self-testing
Data Source
AI summary
A system including a read channel device and a loopback circuit. The read channel device communicates with a hard disk controller module via a read bus and a write bus. The loopback circuit is configured to selectively loop back the write bus to the read bus. The read channel device is configured to generate a write clock for the hard disk controller module to write data on the write bus. The read channel device is configured to generate a read clock for the hard disk controller module to read the data on the read bus. The write clock is independent of the read clock.