Audio Amplifier Input Gain Circuit With Noise-Reducing Voltage Boost
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Solution Overview
Problem
In in-vehicle audio systems, class-D audio amplifier circuits face challenges in reducing thermal noise due to high resistance values needed for capacitors, which are restricted by capacitance limitations in LSI, and the low gain of the input gain circuit amplifies this noise, making it difficult to achieve efficient noise reduction.
Innovation Solution
The audio amplifier circuit incorporates a voltage source generating an internal power supply voltage and a bias voltage, with an input gain circuit having a withstand voltage protection circuit to clamp the output voltage, allowing for increased signal amplitude and reduced thermal noise, while protecting the phase compensation capacitor by setting the bias voltage appropriately and using a withstand voltage protection circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitance value of the feedback capacitor is increased to reduce thermal noise, then the noise performance improves, but the LSI integration becomes difficult due to capacitance value restrictions
Solution Approach 1:
The patent changes the voltage parameter by introducing a voltage doubler circuit that generates a 10V internal power supply voltage (VDD_INT) from a 5V external power supply. This voltage parameter change allows the use of smaller capacitance values while maintaining the same noise performance, as the higher voltage compensates for the reduced capacitance in the noise calculation formula.
Solution Approach 2:
The patent segments the power supply system into two parts: the external 5V power supply and the internal 10V power supply generated by the voltage doubler circuit. This segmentation allows different parts of the circuit to operate at different voltage levels, enabling the feedback capacitor to achieve low noise performance with a smaller capacitance value that can be integrated in LSI.
2Power
If the gain of the input gain circuit is increased to compensate for low signal amplitude, then the signal strength improves, but the thermal noise from high resistance resistors is amplified
Solution Approach 1:
The patent changes the voltage parameter by providing 10V to the input gain circuit through the voltage doubler circuit. This higher voltage supply allows the circuit to achieve the required signal amplitude without needing excessive gain, thereby avoiding amplification of thermal noise from high resistance resistors.
3Object-affected harmful factors
If the withstand voltage of the previous stage is increased to allow higher voltage operation, then the noise performance improves, but the device complexity increases
Solution Approach 1:
The patent introduces a voltage doubler circuit as an intermediary device between the external 5V power supply and the internal circuit blocks. This intermediary generates the required 10V internal power supply voltage and includes protection circuits to prevent excessive voltage from reaching components with lower withstand voltage ratings, thereby simplifying the overall design compared to requiring all components to withstand 10V.
Data Source
AI summary
In an audio amplifier circuit, a power supply terminal receives a power supply voltage. A voltage source generates an internal power supply voltage obtained by multiplying the power supply voltage by a first gain and a bias voltage obtained by multiplying the power supply voltage by a second gain. An input gain circuit amplifies an analog audio signal with reference to the bias voltage. The input gain circuit has an input stage and a gain stage. A phase compensation capacitor is connected to the gain stage. A withstand voltage protection circuit clamps an output voltage of the gain stage to a predetermined clamp voltage.