Synchronization to a start-of-scan detection, and digital generation of

Abstract

A highly accurate and stable, but continuous fixed-phase fixed-frequency, quartz crystal oscillator frequency source, typically of 80 Mhz frequency, is used as the primary frequency standard for (i) synchronized, and (ii) variable, pixel placement timing in a bee-scanning image generator. A fixed-frequency timing chain appropriately synchronized to the scanning energy beam is generated by selecting, in accordance with a sensed start-of-scan condition, from among a number, typically 23, of variably-phase-delayed, typically by less than 1 nanosecond and normally by 0.8 nanosecond, replications of a fixed-phase timing chain that is produced from the crystal oscillator. The synchronized fixed-frequency timing chain so derived is then converted to the required variable-frequency pixel placement timing chain by timing-data-driven recombination of variably-phase-delayed replications, typically 13 such replications at a delay of 1.5 nanoseconds one to the next, of each of (i) the source, fixed-frequency, timing chain and (ii) a 180.degree. phase-shifted version of this source timing chain. The (i) synchronized and (ii) variable-frequency pixel placement timing chain so derived from a fixed-phase fixed-frequency source is both stable and accurate for sub-millimeter precision positioning of typically 32,400+ pixels along scan lines of 45+ centimeters (i.e., 1800 pixels/inch) generated at a typical rate of 540 Hz in, and by, a self-resonant scanning galvanometer laser imager.