| 摘要 |
A position encoder (200) uses a track (202) encoded with a pattern of bit-widths (203) in accordance with a sequence. The sequence may be any sequence having unique subsequences, and may be a pseudo-random noise (PRN) sequence such that each N-bit subsequence occurs only once on the track. Sensors (204, 206) detect transitions between the bits and bit-widths as the track moves with respect to the sensors to provide in-phase and quadrature-phase pick-off signals (208, 210). The pickoff signals are summed and absolute value thresholded (600). The absolute value thresholded sum signal (606) is sampled when the quadrature pairs are in the "00" or "11" quadrants, and latched when the sum signal goes high to distinguish between wide and narrow bit widths. The latch value is shifted into a shift data register for use in determining the position of the encoder track. In the case of a PRN sequence having a length of 2N bits, the position may be an absolute position when the number of valid bits in the shift data register is at least N. The position may be an incremental position when the number of transitions detected is less than N. |
