Triangle Wave Generator Circuit With DC Servo Noise Reduction
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Solution Overview
Problem
Existing Class D amplifiers face challenges in achieving high channel isolation and safe operation over varying load impedances, leading to issues like crosstalk and potential damage to output stages.
Innovation Solution
The implementation of a triangle wave generator circuit that includes a clock generating circuit, current sources, a DC servo circuit, and an output filter to generate a substantially noise-free triangle wave signal, while also limiting the duty cycle and sensing speaker impedance to ensure safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a global triangle ramp generator is used for all channels, then device complexity is reduced, but channel isolation deteriorates causing crosstalk
Solution Approach 1:
The patent divides the global triangle ramp generator into individual per-channel triangle wave generators. Each channel has its own dedicated triangle wave generator that produces isolated triangle waves, preventing crosstalk between channels while maintaining manageable complexity through modular design.
Solution Approach 2:
The patent introduces individual analog buffers between each channel and the triangle wave generator. These buffers act as intermediaries that isolate the triangle wave generation from channel interactions, preventing crosstalk while allowing efficient signal distribution.
2Measurement precision
If the triangle wave frequency is increased to achieve better PWM resolution, then audio signal fidelity is improved, but audio frequency noise in the triangle wave increases
Solution Approach 1:
The patent extracts and removes audio frequency noise from the triangle wave signal using dedicated noise reduction circuits. These circuits specifically target and eliminate audio band noise components while preserving the high-frequency triangle wave characteristics needed for precise PWM modulation.
Solution Approach 2:
The patent employs a DC servo circuit that dynamically adjusts the triangle wave generator parameters to minimize DC voltage and audio frequency noise. The circuit monitors and corrects parameter drift, maintaining optimal operating conditions for low-noise high-frequency triangle wave generation.
3Adaptability or versatility
If the duty cycle is not limited, then the amplifier can operate over a wider range, but the output stage may be damaged due to mismatched speaker loads
Solution Approach 1:
The patent implements preliminary duty cycle limiting that prevents the duty cycle from reaching extreme values. This pre-emptive constraint protects the output stage from damage due to mismatched speaker loads while maintaining sufficient operating range for normal audio reproduction.
Solution Approach 2:
The patent uses feedback circuits that monitor the duty cycle and speaker load conditions, dynamically adjusting the duty cycle limits to protect the output stage while maintaining maximum usable operating range. The feedback mechanism ensures safety without unnecessarily restricting performance.
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 solution effectively reduces crosstalk noise and prevents mismatching of speaker loads, thereby enhancing the reliability and safety of Class D amplifiers.
Implementation Method 1
an output filter circuit adapted to substantially reduce audio frequency noise in the output triangle wave
Implementation Method 2
a DC servo circuit adapted to adjust the first magnitude of the first source current based on a direct current (DC) voltage present in the output triangle wave signal so that the DC voltage on the output triangle wave signal is substantially eliminated
Data Source
AI summary
Described herein is a triangle wave generator circuit for use with a class D amplifier, the triangle wave generator circuit adapted to generate and output a triangle wave signal and comprising: a clock generating circuit adapted to provide a timing signal that generates a period of the output triangle wave; a first current source adapted to provide a first source current at a first magnitude; a first current sink adapted to sink a first sink current at about two times the first magnitude; a DC servo circuit adapted to adjust the first magnitude of the first source current based on a direct current (DC) voltage present in the output triangle wave signal so that the DC voltage on the output triangle wave signal is substantially eliminated; and an output filter circuit adapted to substantially reduce audio frequency noise in the output triangle wave, and generate the output triangle wave signal at a desired peak-to-peak voltage level based on the first source current and first sink current.