Hybrid PWM-PDM Modulation for High-Resolution Optical Control
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Solution Overview
Problem
Existing modulation techniques, such as pulse width modulation and pulse density modulation, face limitations in achieving high resolution without increased period length or incurring high power losses and electromagnetic noise, particularly in microlithography applications where precise control of optical elements is required.
Innovation Solution
A modulation device that splits an N-bit input signal into M-bit and L-bit partial signals, using pulse density modulation on the L-bit signal and pulse width modulation on the M-bit signal, generating a hybrid modulation signal with improved resolution and reduced period length, while minimizing power losses and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse width modulation is used to achieve high resolution, then resolution is improved, but the period of the modulation signal increases
Solution Approach 1:
The N-bit input signal is divided into two parts: M more significant bits and L less significant bits. The more significant bits are processed using pulse width modulation to determine the coarse position, while the less significant bits are processed using pulse density modulation to determine the fine position adjustment. This segmentation allows achieving N-bit resolution without requiring the full period length that would be needed for direct N-bit pulse width modulation.
2Measurement precision
If pulse density modulation is used to maximize switching processes, then resolution is improved, but power losses increase and electromagnetic noise is emitted
Solution Approach 1:
The input signal bits are segmented into more significant bits (processed by PWM) and less significant bits (processed by PDM). The PWM path handles the majority of the signal value with efficient switching, while the PDM path handles only the fine adjustment with minimal switching activity, thereby reducing overall power consumption and electromagnetic noise compared to full PDM.
Data Source
AI summary
A modulation device includes: a signal splitter configured to generate: i) an M-bit wide partial signal comprising M more significant bits of an N-bit wide input signal; and ii) an L-bit wide partial signal comprising L less significant bits of the N-bit wide input signal, where L=N−M; a first modulation unit configured to generate a 1-bit wide pulse density modulation signal on the basis of the L-bit wide partial signal; a summation unit configured to generate an M-bit wide summation signal on the basis of the M-bit wide partial signal and the 1-bit wide pulse density modulation signal; and a second modulation unit configured to generate a 1-bit wide pulse width modulation signal on the basis of the M-bit wide summation signal.