Class-D Amplifier Layout for Inkjet Printhead Noise Reduction
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Solution Overview
Problem
The operation of liquid discharge devices using class-D amplifiers for piezoelectric elements in inkjet printers becomes unstable due to noise effects, especially when switching high-frequency transistors, leading to abnormal oscillations and degraded printing quality.
Innovation Solution
A liquid discharge device configuration with a modulation circuit, a transistor pair, a demodulation unit including an inductor and capacitor, and a specific arrangement of components to minimize noise effects, where the distance between the high side transistor and capacitor is longer than between the inductor and capacitor, and the inductor and capacitor are separated by at least 3 mm to reduce abnormal oscillations and frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the frequency of the modulation signal is raised to enable class-D amplification of the drive signal, then power efficiency is improved, but operation stability deteriorates due to noise effects and abnormal oscillations
Solution Approach 1:
The patent extracts and removes the harmful noise effects from the system by carefully selecting the distance between the capacitor and other components (inductor, high-side transistor) to be greater than or equal to 3 mm. This spatial separation extracts the noise interference from the critical signal paths, allowing the class-D amplifier to operate at high frequencies while maintaining stability.
Solution Approach 2:
The patent applies local quality by creating different spatial zones with different electromagnetic characteristics. By setting specific distance requirements (≥3 mm) between the capacitor and noise-generating components, the patent creates localized regions of reduced electromagnetic interference around the capacitor, while allowing closer positioning in other areas where noise is less critical.
2Device complexity
If the distance between the high side transistor and capacitor is reduced to minimize layout area, then device complexity is reduced, but noise effects on the capacitor increase causing abnormal oscillations
Solution Approach 1:
The patent changes the spatial parameter (distance) between the capacitor and noise-generating components to a specific range (≥3 mm). This parameter change transforms the capacitor's operating environment by reducing its exposure to high-frequency switching noise, thereby preventing abnormal oscillations while maintaining a compact overall layout.
3Device complexity
If the distance between the inductor and capacitor is reduced to minimize layout area, then device complexity is reduced, but frequency variation increases due to parasitic inductance
Solution Approach 1:
The patent converts the potentially harmful parasitic inductance effect into a beneficial outcome by optimizing the spatial relationship between the inductor and capacitor. By setting their distance to ≥3 mm, the patent reduces the parasitic coupling to a level where it no longer causes significant frequency variation, effectively turning the parasitic effect into a manageable parameter that maintains frequency stability.
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 configuration stabilizes the operation of the liquid discharge device, reduces noise effects, and maintains printing quality by ensuring the drive signal includes frequency components necessary for precise ink droplet formation, while optimizing power efficiency and heat management.
Implementation Method 1
a piezoelectric element that is displaced when a drive signal is applied
Implementation Method 2
a demodulation unit including an inductor and a capacitor and that generates a drive signal by smoothing an amplified modulation signal
Data Source
Figure 1
Figure 2
Figure 3~4B
AI summary
A liquid discharge device includes a modulation circuit that generates a modulation signal obtained by pulse-modulating a source signal by self oscillation, a transistor pair which includes a high side transistor and a low side transistor and which generates an amplified modulation signal by amplifying the modulation signal, a demodulation unit which includes an inductor and a capacitor and which generates a drive signal by smoothing the amplified modulation signal, an piezoelectric element that is displaced when the drive signal is applied, a cavity inside which a liquid droplet is filled and whose internal volume is changed by the displacement of the piezoelectric element, and a nozzle provided to discharge liquid inside the cavity according to the change of the internal volume of the cavity. A distance between the high side transistor and the capacitor is longer than a distance between the inductor and the capacitor.