Practical pseudo-asynchronous filter architecture

A method of generating at a variable rate a filtered output using a synchronous filter, wherein the filtered output is accepted periodically by a secondary process with a secondary process period Tbe and the synchronous filter generates the filtered output with a filter sampling time Tf, comprising:

• changing the filter sampling time Tf of the synchronous filter such that the synchronous filter generates the filtered output when the secondary process is able to periodically accept the filtered output;
• accepting a sensor sample by the synchronous filter;
• generating the filtered output from the synchronous filter using the sensor sample;
• and
• accepting the filtered output by the secondary process.

A method of generating at a variable rate a filtered output using a synchronous filter, wherein the filtered output is accepted periodically by a secondary process with a secondary process period Tbe and the synchronous filter generates the filtered output with a filter sampling time Tf, comprising:

• increasing the secondary process period Tbe by an amount such that the secondary process is able to periodically accept the filtered output at substantially the same time the synchronous filter produces the filtered output;
• accepting a sensor sample by the synchronous filter;
• generating the filtered output from the synchronous filter using the sensor sample;
• and
• accepting the filtered output by the secondary process.

A system for use with a secondary process that requires different filtered samples during each of a sequence of input window time intervals, and for providing filtered electronic signal samples, comprising:

• multiple filtered sample lines;
• multiple filters, each periodically receiving a sample of a signal;
• wherein:
• each filter periodically provides its filtered sample sequence to a filtered sample line with a respective filter sampling time Tf, and
• the respective filtered sample sequences are offset in time with respect to one anther so that no filtered sample from any filtered sample sequence overlaps with any filtered sample from any other filtered sample sequence;
• a multiplexer responsive to control signals and coupled to each of the multiple filtered sample lines;
• wherein:
• the multiplexer accepts the respective periodic filtered output of each of the multiple filters, and
• the multiplexer has a multiplexer output;
• and
• control logic providing control signals causing the multiplexer to:
• select from among the filtered sample lines in a sequence results in respective coincidences of respective filtered samples on respective selected filtered sample lines and respective input sample windows for the secondary process, and
• sequentially provide respective filtered samples on respective selected lines as a sequence of filtered input for use by the secondary process.

A lithography source control system comprising:

• a sensor generating a signal;
• multiple filters each periodically accepting a sample of the signal and producing a respective periodic filtered output with a filter sampling time Tf;
• a multiplexer having a multiplexer output and accepting the respective periodic filtered output of each of the multiple filters;
• control logic controlling the multiplexer such that the multiplexer output produces an output sequence of the respective periodic filtered output accepted by the multiplexer;
• and
• a lithography source that is controlled using the output sequence.

A method of exposing a wafer to an electron beam in a microlithography apparatus, comprising:

• acquiring, from a sensor, data indicative of a position of a stage assembly that positions the wafer;
• calculating, from the data, a velocity of the stage assembly and an acceleration of the stage assembly;
• estimating, using the velocity and the acceleration, a future position of the stage assembly;
• determining a difference between the position and the future position;
• and
• adjusting at least one of:
• the position within a predetermined position error, and
• a deflection amount of the electron beam.