Analog Switch Gate Precharge for Low-Flatness Audio Signals
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Solution Overview
Problem
Existing MOS analog switches do not exhibit a low enough flatness characteristic for audio applications and are not suitable for battery-powered devices due to their power consumption and inability to handle negative input signal voltages.
Innovation Solution
A circuit design that includes a first transistor coupled between a signal input and output, with a gate control circuit that pre-charges a capacitor to maintain a substantially constant gate-to-source voltage across the transistor, regardless of input signal variations, eliminating the need for a static discharge path and optimizing performance for battery-powered applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a level shifter with constant current is used to maintain constant gate-to-source voltage, then flatness characteristic is improved, but power consumption increases and it cannot handle negative input signal voltages
Solution Approach 1:
The patent employs periodic charging of the capacitor during the enable phase to establish the gate-to-source voltage, followed by maintenance during the steady state. This periodic action replaces the continuous constant current consumption of traditional level shifters, achieving low power consumption while maintaining flatness characteristic.
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the input signal and the transistor gate. This capacitor mediates the voltage relationship, allowing the gate-to-source voltage to be maintained without requiring continuous current from a level shifter, thus reducing power consumption while preserving signal handling capability including negative voltages.
2Manufacturing precision
If a level shifter circuit is used to regulate gate voltage, then flatness characteristic is improved, but device complexity increases
Solution Approach 1:
The patent extracts the essential function of voltage regulation from the complex level shifter circuit and implements it through a simple capacitor-based mechanism. By taking out only the necessary energy storage and voltage maintenance function, the circuit complexity is dramatically reduced while the flatness characteristic is preserved.
Solution Approach 2:
The capacitor in the patent serves itself by automatically charging to the appropriate voltage during the enable phase and then self-maintaining the gate-to-source voltage relationship during operation. This self-service mechanism eliminates the need for complex active regulation circuits, reducing device complexity while achieving the desired flatness characteristic.
3Use of energy by moving object
If traditional MOS analog switch is used, then power consumption is low, but flatness characteristic is unacceptable for audio applications
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor during an enable phase before the actual signal transmission. This preliminary charging establishes the correct gate-to-source voltage relationship in advance, ensuring that when the switch operates, it maintains constant on-resistance and achieves acceptable flatness characteristic for audio applications while keeping power consumption low.
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 solution achieves a low flatness operating characteristic by maintaining a constant gate-to-source voltage, reducing signal distortion and power consumption, making it suitable for audio applications and battery-powered devices.
Implementation Method 1
a capacitor coupled across the gate-to-source of the first transistor between the first input and the output of the gate control circuit, wherein a voltage stored across the capacitor sets a substantially constant gate-to-source voltage of the first transistor
Data Source
AI summary
An analog switch includes a transistor whose source connected to a signal input and whose drain is connected to a signal output. An output of a gate control circuit is connected to the transistor gate. A first input of the gate control circuit is connected to the source of the transistor. The gate control circuit responds to a logic transition of an enable signal received at a second input by pre-charging a substantially constant gate-to-source voltage across the transistor. This voltage is stored by a gate-to-source connected capacitor. In one steady-state logic condition of the enable signal, the gate control circuit operates to turn off the transistor. In another steady-state logic condition of the enable signal, the gate control circuit permits the signal received at the signal input to drive the gate of the transistor with a voltage offset by the substantially constant gate-to-source voltage stored on the capacitor.