Differential Amplifier Circuit for Printhead Temperature Noise Reduction
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Solution Overview
Problem
Inkjet printing apparatuses face challenges in accurately controlling printhead driving conditions due to high-frequency noise from digital signals interfering with temperature sensor output, leading to errors in temperature detection and reduced reproducibility of printed images.
Innovation Solution
A printing apparatus with a control unit and differential amplifier circuit that matches the wiring resistances of signal lines connected to the temperature sensor, reducing noise interference and enhancing temperature detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If digital signal lines are placed next to the temperature sensor signal line to support the temperature sensor in a semiconductor integrated circuit, then the temperature sensor can be integrated with the digital signal processing circuit, but high-frequency noise from the digital signals is combined with the temperature sensor output signal, resulting in inaccurate temperature detection
Solution Approach 1:
A differential amplifier circuit is introduced as an intermediary between the temperature sensor and the digital signal processing circuit. The differential amplifier detects the small voltage change from the temperature sensor while rejecting common-mode noise from digital signals, thereby enabling accurate temperature detection even when digital signal lines are present in the vicinity.
Solution Approach 2:
The patent applies noise reduction techniques that equalize the impedance characteristics of signal lines to minimize noise coupling. By balancing the electrical characteristics of adjacent signal lines, the patent reduces the harmful effects of high-frequency noise from digital signals on the temperature sensor output.
2Measurement precision
If the DC bias current for the diode temperature sensor is restricted to a predetermined current range to reduce offset in detected voltage, then the offset is reduced, but the DC bias current may raise the substrate potential and cause latch-up in substrate transistor structure
Solution Approach 1:
The patent segments the bias current path by introducing separate current paths for different functional blocks. The temperature sensor receives a controlled bias current that is sufficient to minimize offset but is isolated from the main digital circuit power supply, preventing substrate potential rise and latch-up while maintaining measurement precision.
Solution Approach 2:
Current mirrors and isolation circuits are used as intermediaries to provide the necessary bias current to the temperature sensor without directly connecting it to the main digital circuit power supply. This intermediary structure allows precise control of the bias current while preventing substrate potential interference.
3Manufacturing precision
If a resistor is series-connected to the diode temperature sensor to set the operation resistance to a predetermined value, then the operation resistance is controlled, but the detection sensitivity for the forward voltage of the diode upon temperature change decreases and the S/N ratio drops
Solution Approach 1:
The patent uses a differential amplifier configuration where two matched diodes are used - one as the temperature sensor and the other as a reference. The differential amplifier copies the voltage characteristics of both diodes and outputs only the difference, which corresponds to the temperature-induced voltage change. This copying approach eliminates the need for series resistors while maintaining both operation resistance control and temperature detection sensitivity.
Solution Approach 2:
The patent changes the measurement parameter from absolute voltage to differential voltage. By measuring the voltage difference between two matched diodes rather than the absolute voltage of one diode, the system achieves temperature detection sensitivity without requiring series resistors to control operation resistance.
4Measurement precision
If the period for controlling driving conditions is limited to the interval between printing operations when no ink is discharged, then accurate temperature detection can be achieved without noise interference, but the control period is reduced and continuous printing performance suffers
Solution Approach 1:
The patent enables continuous temperature monitoring and driving condition control during printing operations by using a differential amplifier circuit that can distinguish the temperature sensor signal from high-frequency noise. This allows the control system to continuously adjust driving conditions based on real-time temperature feedback without interrupting the printing process, maintaining both measurement precision and productivity.
Solution Approach 2:
The patent implements continuous feedback control where the differential amplifier circuit continuously monitors the temperature sensor output even during printing operations, and the control system continuously adjusts the driving conditions based on this feedback. This closed-loop feedback mechanism enables accurate temperature compensation during continuous printing, improving both measurement precision and productivity.
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
The solution effectively reduces noise signals combined with the temperature sensor output, minimizing temperature detection errors and maintaining high reproducibility of printed images even during continuous printing operations.
Implementation Method 1
a differential amplifier circuit configured to be incorporated in the control unit, and amplifies a voltage difference between the first signal line and the second signal line to output the amplified voltage difference as temperature information of the printhead
Implementation Method 2
a temperature detection arrangement such as the temperature sensor incorporated in the printhead often uses a diode temperature sensor arrangement which detects the forward voltage of a forward biased p-n junction
Implementation Method 3
a matching circuit configured to make a wiring resistance of the first signal line and a wiring resistance of the second signal line match each other by grounding one of the first signal line and the second signal line via a resistor in the printhead
Data Source
AI summary
A printing apparatus includes a printhead incorporating a temperature sensor, a control unit which controls the printhead, and a flexible cable which connects the printhead and the control unit. The flexible cable includes a first signal line and second signal line which generate voltages corresponding to the temperature of the printhead, and are connected to the temperature sensor. A differential amplifier circuit which is incorporated in the control unit amplifies the voltage difference between the first signal line and the second signal line to output the amplified voltage difference as temperature information of the printhead. A matching circuit makes the wiring resistances of the first signal line and second signal line match each other by grounding either the first signal line or the second signal line via a resistor in the printhead.