Duplicate Feedback Network for Silent Class D Amplifier Startup
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Solution Overview
Problem
Class D amplifiers experience unwanted pop and click noise during power-on and power-off due to the establishment of quiescent voltages, which existing technologies have not adequately addressed.
Innovation Solution
A duplicate feedback resistor network and input section with switches that drive a control circuit to manage the H-bridge switch, allowing differential operation and gradual introduction or removal of offsets to suppress noise during power transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback loop is established in Class D amplifiers to compensate for variations in bus voltages and correct distortion, then amplifier performance and accuracy are improved, but pop and click noise occurs during power-on and power-off due to quiescent voltage establishment
Solution Approach 1:
The patent applies preliminary action by establishing the feedback loop in a controlled sequence during power-on. The feedback network is enabled gradually after the power supply voltage is applied, allowing quiescent voltages to stabilize before full feedback operation begins. This prevents the sudden voltage steps that cause pop and click noise while still achieving accurate distortion compensation.
Solution Approach 2:
The patent implements dynamics by making the feedback loop adaptable to different operating states. During power-on, the feedback network transitions from disabled to enabled state in a controlled manner. During normal operation, the feedback loop dynamically compensates for bus voltage variations. This dynamic behavior allows the system to maintain high accuracy while avoiding noise during transitions.
2Productivity
If quiescent voltages are established quickly during power-on to reduce startup time, then productivity is improved, but pop and click noise increases due to abrupt voltage changes
Solution Approach 1:
The patent uses preliminary action by preparing the feedback network in advance during the power-on sequence. The power supply voltage is applied first to allow capacitors to charge and quiescent voltages to establish, then the feedback network is enabled subsequently. This staged approach maintains reasonable startup speed while preventing abrupt voltage changes that cause noise.
Solution Approach 2:
The patent applies periodic action through the sequential enabling of different feedback network components during power-on. Rather than enabling all feedback paths simultaneously, the system activates them in a timed sequence, allowing each stage to settle before the next is enabled. This periodic activation reduces noise while maintaining efficient startup.
Data Source
AI summary
A circuit and a method are provided for suppressing the pop and click noise during the power on and power off of Class D amplifiers. The technique also suppresses pops and clicks when the Class D amplifier enters or exits standby mode. A duplicate feedback network is used to establish the stable operating points, including offsets in the Class D circuit without turning on the outputs. The technique works by gradually propagating or dissipating the offset through the signal path of a Class D amplifier by swapping the differential outputs using switches to suppress pops and clicks when starting up and shutting down the amplifier.