Dual-Bridge Class-D Amplifier for Above-Supply Signal Swing
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Solution Overview
Problem
Class-D amplifiers face limitations in output power due to the constraints of supply voltage, leading to signal clipping and distortion, especially in mobile devices where the battery voltage is low, and existing solutions like boost converters and charge pumps are inefficient or bulky.
Innovation Solution
A class-D amplifier circuit design that uses dual bridges connected through capacitors to boost the voltage across the load, allowing output signal swings greater than the supply voltage without increasing the supply voltage, utilizing small capacitors that charge during high signal levels to enhance power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the supply voltage is increased to overcome output power limitations, then the output power increases, but the device complexity and power management complexity increase
Solution Approach 1:
The patent changes the voltage parameter dynamically by switching between single-bridge and dual-bridge configurations based on the input signal amplitude. When the signal exceeds the supply voltage threshold, the system automatically activates the dual-bridge configuration to provide higher output voltage and power, and switches back to single-bridge when the signal is within the supply voltage range, thereby avoiding continuous high-power consumption and complex power management.
Solution Approach 2:
The patent implements a dynamic system where the amplifier configuration is not fixed but adapts in real-time based on signal conditions. The controller monitors the input signal amplitude and dynamically reconfigures the bridge circuitry, enabling the system to optimize between power efficiency and output power delivery as needed.
2Power
If a full bridge circuit is used to double the output voltage swing, then the output power increases, but the circuit complexity increases
Solution Approach 1:
The patent divides the amplifier into two separate bridge circuits (first bridge and second bridge) that can operate independently or in combination. This segmentation allows the system to use only the necessary number of bridges based on the signal requirements, reducing the effective circuit complexity when full power is not needed while maintaining the capability for high power output when required.
Solution Approach 2:
The patent implements dynamic reconfiguration where the controller selectively activates either the first bridge, the second bridge, or both bridges in parallel depending on the input signal amplitude. This dynamic approach allows the system to maintain simplicity during normal operation while providing enhanced power capability when needed.
3Power
If the amplifier operates at high power levels continuously, then the output power capability is maximized, but the energy consumption increases
Solution Approach 1:
The patent employs dynamic operation where the amplifier switches between low-power single-bridge mode and high-power dual-bridge mode based on real-time signal conditions. The controller monitors the input signal amplitude and activates the dual-bridge configuration only when the signal exceeds the supply voltage threshold, thereby maximizing power capability when needed while minimizing energy consumption during normal operation.
Solution Approach 2:
The patent implements periodic monitoring and switching between operational modes. The controller continuously evaluates the input signal and periodically reconfigures the bridge circuitry as needed, allowing the system to maintain optimal energy efficiency while being ready to provide high power output when signal conditions require it.
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 design effectively increases the output power by doubling the voltage across the load, reducing distortion and power limitations, while using smaller capacitors that do not require long-term charge storage, thus being suitable for portable devices.
Implementation Method 1
A first capacitor having a positive terminal connected to the drains of both transistors of the first half bridge and a negative terminal connected to the drains of both transistors of a third half bridge; and a second capacitor having a positive terminal connected to the drains of both transistors of the second half bridge and a negative terminal connected to the drains of the transistors of a fourth half bridge
Data Source
AI summary
An apparatus and method are disclosed for providing output signal swings that are greater than the supply voltage in a class-D amplifier. The amplifier circuit boosts the voltage across the amplifier load, such as a loudspeaker, by using capacitors to “charge pump” the voltage across the load and thus increase the voltage temporarily. This is done by using two or more output bridges rather than one, and connecting the bridges through the capacitors. For signals of less than the supply voltage, only an inner bridge, similar to a full bridge of the prior art, operates. For signals above the supply voltage, an outer bridge charges capacitors, which are then used to ‘boost’ the voltage on the bridge output for the short period of the Class-D switching period. Thus, only relatively small value boosting capacitors are needed, as they do not need to supply charge for very long.