MOS Low-Pass Filter Biasing for Fast Power-On Stabilization
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Solution Overview
Problem
Conventional low pass filters take a long time to reach a steady state upon power-on due to the charging time required for the filter capacitor.
Innovation Solution
A low pass filter design incorporating a first-conductivity-type MOS transistor, an electrostatic capacitor, a buffer circuit, and a bias circuit, which allows for rapid charging of the capacitor upon power-on without additional control circuits, utilizing a MOS transistor as a resistor and an operational amplifier circuit to achieve quick stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional low pass filter with a resistor and electrostatic capacitor is used, then noise removal is achieved, but the time to reach steady state upon power-on is long
Solution Approach 1:
The patent changes the operating parameters of the MOS transistor by applying a gate voltage that is higher than the power supply voltage during the startup phase. This temporary parameter change enables the transistor to conduct with much lower on-resistance, allowing rapid charging of the capacitor and quick establishment of the steady state, thereby resolving the contradiction between noise removal capability and startup time
Solution Approach 2:
The patent implements preliminary action by using a bootstrap circuit to pre-charge the gate of the MOS transistor before the main filtering operation begins. This preliminary charging action prepares the transistor for low-resistance conduction, enabling the capacitor to charge quickly upon power-on and reducing the time to reach steady state while maintaining the noise removal function
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
Enables the low pass filter to reach a steady state quickly upon power-on, reducing the time required for stabilization and minimizing current consumption.
Implementation Method 1
an electrostatic capacitor, a buffer circuit, a bias circuit
Data Source
AI summary
A low pass filter and a semiconductor device including the low pass filter are capable of quickly reaching a steady state upon power-on. The low pass filter includes a first first-conductivity-type MOS transistor, an electrostatic capacitor, a buffer circuit, a bias circuit, an input terminal, and an output terminal. The input terminal is connected to a source terminal of the first first-conductivity-type MOS transistor. A drain terminal of the first first-conductivity-type MOS transistor is connected to a first terminal of the electrostatic capacitor, the output terminal, and an input terminal of the buffer circuit. An output terminal of the buffer circuit is connected to an input terminal of the bias circuit. An output terminal of the bias circuit is connected to a gate terminal of the first first-conductivity-type MOS transistor.