Open-Drain Signal Output Circuit With Low-Pass Noise Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Signal output circuits with inverting amplifier circuits face issues with noise interference, leading to erroneous operations in the output transistor due to noise components entering through the feedback capacitor, necessitating external noise suppression devices.
Innovation Solution
A signal output circuit with an inverting amplifier and a low-pass filter connected between the input and output terminals, along with a bridge circuit and clamping transistor configuration, effectively removes noise components and prevents them from entering the internal circuit, eliminating the need for external noise suppression devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedback capacitor is connected between input and output terminals of the inverting amplifier circuit, then the inverting amplification operation is enabled, but noise components enter through the feedback capacitor causing erroneous operations in the output transistor
Solution Approach 1:
A diode is introduced as an intermediary component between the feedback capacitor and the output transistor. The diode's anode is connected to the inverting input terminal and its cathode to the output terminal, creating a protective barrier that blocks noise components from reaching the output transistor while allowing the feedback capacitor to function normally in the inverting amplification circuit.
Solution Approach 2:
The diode is positioned in advance to prevent noise interference before it can cause erroneous operations. By connecting the diode in parallel with the feedback capacitor with opposite polarity, the circuit proactively blocks potential noise components from entering the output transistor, preventing harmful effects before they occur.
2Reliability
If external noise suppression devices are added to prevent noise interference, then noise immunity is improved, but device complexity increases
Solution Approach 1:
The noise suppression function is merged with the existing feedback capacitor by connecting a diode in parallel with it. This integration allows the circuit to maintain its inverting amplification functionality while incorporating noise suppression capability, avoiding the need for separate external noise suppression devices and reducing overall circuit complexity.
Solution Approach 2:
The diode serves multiple functions within the circuit: it protects the output transistor from noise interference, works in conjunction with the feedback capacitor for signal processing, and maintains the inverting amplification operation. This multi-functionality eliminates the need for dedicated external noise suppression components.
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 proposed solution significantly reduces noise interference, enhancing noise immunity and preventing erroneous operations in the output transistor, as demonstrated by improved withstand voltages and reduced noise amplitudes across various frequency ranges.
Implementation Method 1
a low pass filter connected between an input terminal and an output terminal of the inverting amplifier circuit
Data Source
AI summary
A signal output circuit includes an inverting amplifier circuit, a feedback capacitor and a low pass filter. The inverting amplifier circuit includes an input terminal and an output terminal. The inverting amplifier circuit executes an inverting amplification based on an input signal to output a signal to the output terminal at a pull-up state. An output stage of the inverting amplifier circuit is an open collector or an open drain. The feedback capacitor is connected between the input terminal and the output terminal of the inverting amplifier circuit. The low pass filter has an input and an output. The input of the low pass filter is connected to the output terminal of the inverting amplifier. The output of the low pass filter is connected to the feedback capacitor.