Audio Switch Gate Linearization for Low-THD USB-C Analog Signals
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Solution Overview
Problem
The challenge in wireless communication devices is the non-linearity and distortion introduced by large transistors used to isolate circuitry from overvoltage conditions, which affect audio signal transmission through USB-C ports.
Innovation Solution
Implementing a gate driving circuit with a digital-to-analog converter (DAC) and buffer to stabilize the gate-source voltage of MOSFET switches, using gain-adjusted audio signals to maintain a constant impedance and reduce total harmonic distortion (THD).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large transistors are used to isolate circuitry from overvoltage conditions, then circuit protection is improved, but non-linearity and distortion of audio signals increase
Solution Approach 1:
The patent changes the voltage parameter applied to the gate of the transistor. Instead of using a fixed gate voltage, the system dynamically adjusts the gate voltage to track the audio signal voltage, thereby changing the operating parameters of the transistor to maintain linearity while providing protection.
Solution Approach 2:
The patent implements a feedback mechanism where the audio signal voltage is fed back to the gate driving circuit, which then adjusts the gate voltage accordingly. This feedback loop ensures that the transistor operates in a linear region while still providing overvoltage protection when needed.
2Reliability
If large transistors are used for isolation, then overvoltage protection is improved, but impedance stability deteriorates
Solution Approach 1:
The patent dynamically changes the gate voltage parameter to match the audio signal voltage, which stabilizes the impedance of the transistor. By tracking the signal voltage, the transistor's impedance remains constant despite the large transistor size used for protection.
Solution Approach 2:
The patent maintains equipotential conditions by ensuring the gate voltage follows the audio signal voltage. This keeps the voltage differential across the transistor constant, thereby stabilizing the impedance and preventing distortion.
3Device complexity
If fixed gate voltage is applied to MOSFET switch, then circuit simplicity is improved, but audio signal quality deteriorates due to THD
Solution Approach 1:
The patent uses feedback by connecting the audio signal output back to the gate driving circuit. This feedback allows the gate voltage to be dynamically adjusted based on the actual audio signal voltage, reducing THD while adding necessary complexity to the control circuitry.
Solution Approach 2:
The patent introduces a gate driving circuit as an intermediary between the audio signal amplifier and the MOSFET switch. This intermediary circuit processes the audio signal and generates the appropriate gate voltage, mediating between the simple fixed-voltage approach and the complex dynamic control needed for low distortion.
Data Source
AI summary
A wireless device may include a plug that is shared by high speed data, analog audio signals, and power. Switches may be included on wires between the plug and the circuits that provide the high-speed data, analog audio signals and power to isolate those circuits from overvoltage conditions. Linearizer circuits may be included to provide gate driving signals to the switches, e.g., during transmission of analog audio signals. The linearizer circuits may include digital-to-analog converters to apply a gain factor to analog audio signals.