MOSFET Analog Switch With Dynamic Gate Bias for Low Distortion
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Solution Overview
Problem
Conventional analog switches using transfer gates introduce distortion in analog signals due to fluctuations in MOSFET gate-source voltages, particularly when handling signals like audio and video signals, leading to poor quality transmission.
Innovation Solution
An analog switch design incorporating a first N-channel MOSFET between input and output terminals, with a resistor connecting the MOSFET gate to a fixed voltage terminal, and additional capacitors and diodes to stabilize the gate voltage, reducing ON-resistance fluctuations and signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a transfer gate with fixed gate voltage is used, then the analog switch can be constructed with simple circuit configuration, but the gate-source voltage fluctuates with the input signal causing distortion in the analog signal
Solution Approach 1:
The patent applies the dynamics principle by making the gate voltage dynamic instead of fixed. The gate voltage is adjusted according to the input signal voltage to maintain a constant gate-source voltage difference. This is achieved by applying a control voltage to the gate that varies with the input signal, thereby keeping the MOSFET's ON resistance constant and eliminating signal distortion while maintaining relatively simple circuit configuration.
2Manufacturing precision
If the gate voltage is adjusted to reduce distortion, then signal transmission accuracy improves, but the circuit configuration becomes more complex requiring additional voltage control mechanisms
Solution Approach 1:
The patent implements feedback by using the input signal itself to control the gate voltage. The control voltage applied to the gate is derived from or responds to the input signal voltage, creating a feedback mechanism that automatically adjusts the gate-source voltage difference to remain constant. This feedback approach reduces signal distortion while avoiding the need for complex external voltage control circuits.
Solution Approach 2:
The patent applies self-service by enabling the input signal to directly control the gate voltage without requiring external control circuits. The MOSFET's gate voltage is self-adjusted based on the input signal level, allowing the device to regulate its own operating conditions and maintain constant ON resistance without additional complexity from external control mechanisms.
3Device complexity
If conventional transfer gate is used for audio signal transmission, then the circuit remains simple, but the fluctuation in ON resistance causes poor sound quality
Solution Approach 1:
The patent applies dynamics by making the gate voltage dynamic and signal-dependent. The gate voltage changes in response to the audio input signal to maintain a constant gate-source voltage difference, thereby keeping the ON resistance constant throughout the signal cycle. This dynamic adjustment eliminates the distortion that would otherwise degrade sound quality while maintaining a relatively simple circuit configuration suitable for audio applications.
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 design effectively suppresses gate-source voltage fluctuations, thereby reducing signal distortion and maintaining signal quality, especially when connected to loads with low impedance like speakers or headphones, and eliminates the need for negative bias voltage, simplifying the circuit configuration.
Implementation Method 1
the input terminal and the gate are coupled by the gate-source capacitance (or the gate-drain capacitance), and accordingly, the gate voltage changes in phase with the input signal
Implementation Method 2
the first fixed voltage terminal and the gate of the first MOSFET are connected in a high-impedance state by means of the first resistor
Data Source
AI summary
An analog signal is input to an input terminal. An analog signal is output via an output terminal. A first transistor is an N-channel MOSFET, and is provided between the input terminal and the output terminal. A first resistor is provided between the gate of the first transistor and a first fixed voltage terminal (power supply terminal), which sets the gate of the first transistor to a high-impedance state.