Bootstrapped MOS Analog Multiplexer for Harmonic-Free Switching
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Solution Overview
Problem
Analog multiplexers with metal-oxide-silicon (MOS) transistors introduce harmonics into the output signal due to varying resistance when the transistor is enabled, which is undesirable.
Innovation Solution
The multiplexer employs two bootstrap circuits coupled to the source and gate terminals of the transistor, operating in alternate phases to maintain a constant gate-to-source voltage (VGS), ensuring a constant resistance of the transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a MOS transistor is used as the main pass switch in an analog multiplexer, then the multiplexer can pass high frequency analog input signals, but the varying resistance of the transistor introduces harmonics into the output signal
Solution Approach 1:
The bootstrap circuit charges a capacitor to a predetermined voltage level before the MOS transistor is activated. This preliminary charging ensures that when the transistor turns on, the gate-to-source voltage is already at the correct level, establishing constant resistance before the signal passes through, thereby preventing harmonic distortion.
Solution Approach 2:
The invention changes the gate-to-source voltage parameter of the MOS transistor from a variable state to a constant state by using the bootstrap circuit to maintain a fixed voltage difference. This parameter stabilization ensures constant resistance during signal transmission, eliminating the harmonic distortion caused by resistance variations.
2Reliability
If the gate to source voltage of the MOS transistor is not maintained constant, then the transistor resistance varies, but maintaining constant VGS requires additional bootstrap circuitry
Solution Approach 1:
The bootstrap circuit uses the existing signal voltage at the source terminal to automatically adjust and maintain the gate voltage. The capacitor in the bootstrap circuit charges itself from the source voltage, and this self-charging mechanism maintains constant VGS without requiring external control circuits, thereby reducing overall system complexity while ensuring reliable constant resistance.
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 approach prevents the introduction of harmonics into the output signal, allowing for reliable signal transmission from the input to the output without distortion.
Implementation Method 1
The bootstrap circuit includes a capacitor configured to be coupled between the source and the gate during a first phase and to be decoupled from the source and the gate during a second phase
Data Source
AI summary
A multiplexer includes an input, an output, and a main switch configured to pass a signal from the input to the output. The multiplexer includes two bootstrap circuits that collectively maintain a constant voltage between terminals of the main switch during alternating phases.