Class-D H-Bridge Zero-Crossing Control Near Supply Rails
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Class-D audio amplifiers and haptic drivers with differential H-bridge output stages face inefficiency and distortion at low output amplitudes due to high effective output impedance near power supply rails, limiting their ability to control output signals effectively.
Innovation Solution
The implementation of a Class-D amplifier circuit with a control logic system that selectively operates between single-ended and differential modes, using high-side and low-side switches to manage output rail voltages and modulators, allowing for efficient operation near power supply rails by adjusting the quiescent operating point and preventing simultaneous activation of both high-side switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the amplifier operates with a low-amplitude output signal near the power supply rails, then the output voltage can reach the rails, but the effective output impedance of the switching devices rises rapidly causing distortion and reducing control capability
Solution Approach 1:
The patent implements dynamic switching between two operating modes: single-ended mode for low-amplitude signals near the rails and differential mode for higher amplitude signals. The control circuit dynamically selects the appropriate mode based on signal conditions, allowing the amplifier to maintain low output impedance and good control accuracy across the full operating range while still achieving rail-to-rail voltage swing capability.
2Reliability
If the common-mode voltage is set between the power supply rails to avoid distortion, then signal control is improved, but the potential signal swing and efficiency are reduced
Solution Approach 1:
The system dynamically adjusts the common-mode voltage setting based on operating conditions. In single-ended mode, the common-mode voltage can be set near the rails for maximum swing efficiency. In differential mode, the common-mode voltage is set between the rails for optimal control accuracy. This dynamic adaptation allows the amplifier to achieve both high efficiency and good signal control depending on the operating mode.
Solution Approach 2:
The patent segments the operating range into two distinct modes: single-ended operation for low-amplitude signals where efficiency is prioritized, and differential operation for higher amplitude signals where control accuracy is prioritized. This segmentation allows each mode to be optimized for its specific purpose without compromise.
3Power
If both driver circuits are actively operated for full differential output, then output power is increased, but device complexity and control difficulty increase
Solution Approach 1:
The control circuit dynamically determines when to activate one or both driver circuits based on the input signal characteristics and desired output level. For low-amplitude signals, only one driver circuit operates in single-ended mode, simplifying control. For higher amplitude signals, both driver circuits are activated in differential mode to deliver full output power. This dynamic control strategy manages complexity while maintaining full power capability when needed.
Data Source
AI summary
Class-D amplifier circuits provide operation with low-distortion zero crossings outside of a unipolar power supply voltage range. The amplifiers include a first H-bridge driver circuit and a second H-bridge driver circuit. The class-D amplifier circuits also include a control circuit having an input for receiving an input signal to be reproduced by the class-D amplifier circuit. The control circuit has outputs coupled to inputs of the first and second H-bridge drivers, and includes one or more modulators. The control circuit selects between actively operating a selected one of the driver circuits or both, according to the signal to be reproduced, while setting an unselected driver circuit to turn either a high-side switch or a low-side switch of the unselected one of the first driver circuit or the second driver circuit fully on for at least some cycles of the one or more modulators.