Analog Switch Circuit with Bootstrap Charging for Low-Frequency Signals
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Solution Overview
Problem
Conventional analog switch circuits fail to maintain constant ON-resistance for low-frequency signals, leading to signal waveform distortion and are not suitable for continuous signal operation due to repetitive ON and OFF operations.
Innovation Solution
The proposed analog switch circuit employs a field-effect transistor with capacitors and switching elements to maintain a constant voltage between the gate and source, reducing ON-resistance variations and enabling continuous operation across a wide bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bootstrap circuit is used to maintain constant ON-resistance, then ON-resistance can be maintained for high frequency signals, but the circuit cannot operate continuously and is not suitable for low frequency signals
Solution Approach 1:
The patent implements continuous charging of the bootstrap capacitor through a dedicated charging circuit that operates independently of the switch timing. This allows the capacitor to maintain its charged state continuously, enabling the analog switch to remain in the ON state continuously without repetitive ON/OFF operations, thus supporting low frequency signals while maintaining constant ON-resistance
Solution Approach 2:
The charging circuit pre-charges the bootstrap capacitor to the required voltage level before the switch needs to be activated. This preliminary charging action ensures that the capacitor maintains sufficient voltage to keep the switch ON continuously, rather than requiring periodic recharging that would cause repetitive ON/OFF operations
2Reliability
If only up to 1/2 VDD is applied between gate and source in conventional circuits, then circuit complexity is reduced, but ON-resistance cannot be sufficiently reduced
Solution Approach 1:
The patent changes the voltage parameter applied between gate and source from the conventional limit of 1/2 VDD to a higher voltage level by utilizing a bootstrap capacitor charged to VDD. This parameter change enables the MOS transistor to achieve lower ON-resistance by increasing the gate-source voltage differential, improving switch performance without fundamentally changing the circuit topology
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 solution effectively reduces signal distortion and maintains constant ON-resistance, allowing the analog switch circuit to operate effectively with low-frequency signals and wide bandwidth, preventing waveform distortion.
Implementation Method 1
a first capacitance to store electric charge; a second capacitance to store electric charge
Data Source
AI summary
An analog switch circuit that includes a first field-effect transistor, a source of which is coupled to a first switch terminal, and a drain of which is coupled to a second switch terminal; a first capacitance storing electric charge; a second capacitance storing electric charge; a first switch circuit that couples the first capacitance between a direct current voltage node and a reference potential node; a second switch circuit that couples the first capacitance and the second capacitance in parallel; and a third switch circuit that couples the second capacitance between a gate and the source of the first field-effect transistor.