PICA system timing measurement & calibration
AssigneeCredence Systems Corporation
InventorKenneth R. Wilsher
Life of this patent
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Abstract
PICA probe system methods and apparatus are described, including methods and apparatus for calibrating an event timer having a coarse measurement capability in which time intervals defined by clock boundaries are counted and a fine measurement capability in which time between boundaries is interpolated using a voltage ramp.
Claims18
A method of calibrating a timer having a coarse measurement capability in which time intervals defined by boundaries are counted and a fine measurement capability in which time between boundaries is interpolated using a voltage ramp, comprising:
- a. Determining alignment of the voltage ramp relative to a reference-clock signal having a known relationship to the boundaries;
- b. Sampling the voltage ramp at a plurality of known times relative to the boundaries;
- and
- c. Determining slope of the voltage ramp as a function of time from the voltage samples.
Apparatus having an event timer and comprising:
- a. A coarse-measurement counter for counting time intervals defined by boundaries,
- b. A fine-measurement interpolator employing a voltage ramp to measure a time delay of less than one of the time intervals;
- c. A source of an interval-clock signal at a first frequency and a reference-clock signal at a second frequency with a defined phase relationship between the interval-clock signal and the reference-clock signal;
- d. An analog-to-digital converter for sampling the voltage ramp at a plurality of known times relative to the boundaries to obtain voltage samples from which slope of the voltage ramp can be calculated.
A PICA probe system comprising:
- a. A PICA collection camera;
- b. Acquisition electronics responsive to strobe pulses from the PICA collection camera representing photon-detection events for collecting data about such events, including a timing subsystem having a coarse-measurement counter for counting time intervals defined by boundaries and a fine-measurement interpolator employing a voltage ramp to measure a time delay of less than one of the time intervals;
- and
- c. A workstation having a processor in communication with the PICA collection camera and the acquisition electronics for controlling operation and for processing data collected by the acquisition electronics.
Dependencies are inferred from the claim text.