PWM Signal Amplifier Level Shifting for Low-Noise Audio Output
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional signal amplifiers for vehicle-mounted audio devices face issues with noise and increased output impedance due to the use of midpoint voltage as a reference voltage, leading to adverse effects on audio characteristics and inefficiencies caused by the need for a negative power supply that supplies large current, resulting in degraded power efficiency and increased costs and circuit area.
Innovation Solution
A signal amplifier configuration that uses a pulse width modulator driven by both positive and negative power supplies with a reference voltage set to GND, and a power amplifier driven by a single positive power supply with a reference voltage set to a middle value, eliminating the need for a negative power supply and reducing noise and output impedance, while allowing for feedback control and various input/output signal formats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a midpoint voltage between positive power supply and ground is used as reference voltage, then the circuit can operate with single power supply, but noise and output impedance increase causing adverse effect on audio characteristic
Solution Approach 1:
The patent divides the power supply system into two independent parts: the pulse width modulator uses a negative power supply with GND reference, while the power amplifier uses a positive power supply with midpoint reference. This segmentation allows each component to operate with its optimal reference voltage without interfering with the other, resolving the contradiction between single power supply operation and audio quality.
Solution Approach 2:
The level shifter acts as an intermediary component that converts the PWM signal from the negative reference domain to the positive reference domain. This mediator enables the signal to transition between different reference voltage domains, allowing the pulse width modulator and power amplifier to use different reference voltages while maintaining proper signal transmission.
2Reliability
If a negative power supply that supplies large current is used, then the reference voltage can be properly established, but power efficiency degrades and cost and circuit area increase
Solution Approach 1:
The patent extracts the high-current negative power supply requirement only from the pulse width modulator section, while the power amplifier section operates with a simple positive power supply. This extraction eliminates the need for a high-current negative power supply in the overall system, improving power efficiency while maintaining reference voltage stability where needed.
Solution Approach 2:
The patent applies different power supply qualities to different parts of the circuit: the pulse width modulator receives a high-current negative power supply locally where reference voltage stability is critical, while the power amplifier uses a lower-power positive supply where high current is not required. This local differentiation optimizes both reliability and power efficiency.
Data Source
AI summary
A signal amplifier includes a pulse width modulator, a level shifter, and a power amplifier. The pulse width modulator is driven by a positive power supply and a negative power supply, and a reference voltage of the pulse width modulator is set to a GND. The power amplifier is driven by a positive power supply, and a reference voltage of the power amplifier is set to a middle value between the positive power supply and the GND. The level shifter shifts a voltage level of a first PWM signal whose high level corresponds to the positive power supply of the pulse width modulator and whose low level corresponds to the negative power supply of the pulse width modulator, to a voltage level of a second PWM signal whose high level corresponds to the positive power supply of the power amplifier and whose low level corresponds to the GND.