PWM feedback control by using dynamic pulse-to-pulse error compensation

An exposure apparatus comprising:

• an imaging system for imaging a pattern onto an article;
• a stage device for supporting the article for imaging;
• a driver connected to the stage device positioning the stage device relative to the imaging system, the drive means comprising a PWM system that delivers power in response to an input signal, the PWM system comprising:
• a pulse width modulator;
• a controller configured to control the modulator to generate a sequence of pulses representing a pulse-width modulated signal in response to the input signal, wherein at least some of the pulses include modulation error;
• and
• a feedback system connected to the controller and the pulse width modulator, the feedback system feeding the modulation error for each pulse from the modulator to the controller;
• wherein the controller is further configured to determine the modulation error in each pulse and apply the modulation error for each pulse to respective immediate following pulses in the sequence of pulses to compensate for the modulation error in each pulse.

A method of controlling a pulse width modulator to deliver power to a load in response to an input signal, comprising the steps of:

• controlling the modulator to generate a sequence of pulses representing a pulse-width modulated signal in response to the input signal, wherein at least some of the pulses include modulation error;
• feeding the modulation error for each pulse from the modulator to the controller;
• determining the modulation error in each pulse;
• and
• applying the modulation error for each pulse to respective immediate following pulses in the sequence of pulses to compensate for the modulation error in each pulse.

A PWM system that delivers power to a load in response to an input signal, comprising:

• a pulse width modulator;
• a controller connected to the pulse width modulator, the controller controlling the pulse width modulator to generate a sequence of pulses in response to the input signal;
• and
• a detector connected to the controller, the detector determining value related to the error of the pulse based on the information of the pulse and its corresponding ideal pulse;
• wherein the controller makes the pulse width modulator generate compensated pulse by applying the value related to the error for at least one pulse to respective immediate following pulses in the sequence of pulses.