Multi-Level PWM Signal Generation for Flow Rate Measurement
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Solution Overview
Problem
Flow rate measuring devices face challenges in achieving both high accuracy and rapid response speed while using PWM type D/A converters, as they often suffer from residual ripple and instability in analog signal due to low voltage accuracy and noise sensitivity, which is critical in semiconductor manufacturing applications.
Innovation Solution
The device incorporates a PWM signal generating circuit that outputs multiple specified voltage levels, allowing for the selection of two adjacent voltage levels and setting a duty ratio to generate a PWM signal, which is then smoothed by a conversion circuit to produce an accurate analog signal, stabilizing the high and low levels of the PWM signal and reducing ripple without compromising response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the time constant of the lowpass filter is increased to reduce residual ripple and stabilize the analog signal, then the ripple is reduced and signal stability is improved, but the response speed deteriorates and the measured flow rate cannot be immediately reflected
Solution Approach 1:
The patent segments the PWM signal generation into multiple voltage levels (three or more specified voltage levels) instead of using a simple binary PWM signal. By dividing the voltage range into multiple levels and selecting appropriate levels based on the measured flow rate value, the signal transitions more smoothly, reducing residual ripple without requiring a large time constant, thus maintaining fast response speed.
2Device complexity
If a PWM type D/A converter is used for simple and inexpensive configuration, then device complexity is reduced and cost is lowered, but voltage accuracy is insufficient and the analog signal becomes unstable due to noise sensitivity
Solution Approach 1:
The patent changes the voltage level parameters of the PWM signal by introducing multiple specified voltage levels (V1, V2, V3, ...) instead of using only the standard digital power supply voltage and common voltage. By selecting from these pre-defined stable voltage levels based on the measured flow rate, the analog signal accuracy is improved while maintaining the simplicity of the PWM converter configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the production of an analog flow rate signal with high accuracy and improved response speed, minimizing residual ripple and maintaining stability, essential for precise flow rate measurements in semiconductor processes.
Implementation Method 1
the PWM type D/A converter is one that smooths the PWM signal through a lowpass filter to convert to an analog signal
Data Source
AI summary
To achieve both response speed and accuracy required for a flow rate measuring device without sacrificing the simplicity and inexpensiveness of a PWM type D/A converter, the flow rate measuring device includes an analog conversion part adapted to convert a digital signal indicating a measured flow rate value to an analog signal. In addition, the analog conversion part includes: a PWM signal generating circuit that can output three or more specified voltages is configured to, on the basis of the measured flow rate value indicated by the digital signal, select two adjacent voltages, as well as on the basis of the measured flow rate value indicated by the digital signal, set a duty ratio to generate a PWM signal of which a high level and a low level are the two selected voltages, respectively; and a conversion circuit that smooths the PWM signal to convert to the analog signal.