Class D Audio Circuit Bias Control to Prevent Unmute Surge Current
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Solution Overview
Problem
Class D amplifier circuits with analog inputs experience a surge current when the mute control signal is deactivated, as the output voltage deviates from the periodic signal range, leading to high current flow through the high-side transistor and filter components.
Innovation Solution
Incorporating a class D amplifier circuit with a bridge circuit, integrator, periodic voltage generating circuit, and comparator that outputs a predetermined bias voltage during mute periods, preventing large current flows by setting the bias voltage within the periodic voltage range and switching the bridge circuit accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mute control signal is deactivated, then the audio output is restored, but a surge current flows through the high-side transistor and filter components
Solution Approach 1:
The integrator outputs a predetermined bias voltage during the mute period to prepare the control signal in advance. This preliminary action ensures that when mute is deactivated, the PWM comparator receives a controlled bias voltage that prevents the output pulse signal from immediately jumping to a high level, thereby avoiding surge current while readying the audio output for restoration.
Solution Approach 2:
The integrator acts as an intermediary between the mute control signal and the PWM comparator. It processes the mute control signal and outputs a predetermined bias voltage during mute periods, mediating the transition when mute is deactivated. This intermediary function ensures smooth transition and prevents direct coupling between the mute signal and PWM output that would cause surge current.
2Measurement precision
If the integrator integrates the difference between input and feedback signals, then accurate audio signal processing is achieved, but the output voltage deviates from the periodic signal range when mute is deactivated causing high current
Solution Approach 1:
The integrator dynamically changes its output behavior based on the mute control signal state. During mute periods, it outputs a predetermined bias voltage instead of integrating the audio signal difference. This dynamic switching allows the system to maintain accurate audio processing during normal operation while preventing voltage deviation and high current during mute transitions.
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
Effectively inhibits current surges when the mute state is deactivated, ensuring stable operation and preventing excessive current flow through filter components.
Implementation Method 1
an integrator, integrating and outputting a difference between an input signal and a feedback signal corresponding to an output signal generated at the output terminal in a non-mute period in which a mute control signal is negated, and outputting a predetermined bias voltage in a mute period in which the mute control signal is asserted
Implementation Method 2
a periodic voltage generating circuit, generating a periodic voltage of a triangular wave or sawtooth wave
Implementation Method 3
a comparator, comparing an output of the integrator with the periodic voltage
Implementation Method 4
a driver, switching the bridge circuit according to an output of the comparator in the non-mute period, and fixing an output of the bridge circuit in the mute period
Data Source
AI summary
The present disclosure provides an audio circuit capable of inhibiting a current when mute is deactivated. An output terminal of a class D amplifier circuit is connected to an electroacoustic conversion element through a low-pass filter. An output node of a bridge circuit is connected to the output terminal. An integrator integrates and outputs, in a non-mute period in which a mute control signal is negated, a difference between an input signal and a feedback signal corresponding to an output signal generated at the output terminal, and outputs a predetermined bias voltage in a mute period in which the mute control signal is asserted. A PWM comparator compares the output of the integrator with a periodic voltage. A driver switches, in the non-mute period, the bridge circuit according to an output of the PWM comparator, and fixes an output of the bridge circuit in the mute period.