Signal Path Noise Transfer Control for Charge Pump Audio Noise
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Solution Overview
Problem
Personal audio devices face challenges in maintaining dynamic range and reducing noise due to magnitude droop in both analog and digital signal paths, which affects the efficiency of power amplifiers and battery life, and existing solutions do not adequately address these issues.
Innovation Solution
The implementation of a signal path with digital compensation filters to correct for magnitude droop, a delta-sigma modulator for noise shaping, and a charge pump operating at a frequency matching a zero of the modulator noise transfer function to minimize harmonic distortion noise, ensuring a flat passband response and efficient power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high gain is applied to the power amplifier to increase dynamic range, then the dynamic range is improved, but noise in the audio output signal increases and may mask lower-intensity audio signals
Solution Approach 1:
The signal path is divided into separate analog and digital portions, each with its own gain control. The analog signal path portion includes the power amplifier, while the digital signal path portion includes digital gain control. This segmentation allows independent optimization of each path to manage noise and dynamic range separately.
Solution Approach 2:
The patent applies gain control by changing the gain parameter in both digital and analog domains. The digital gain is adjusted based on the magnitude of the output signal, and the analog gain is similarly controlled. This dynamic parameter adjustment allows the system to maintain low noise while preserving dynamic range by reducing gain when signal levels are low.
2Loss of energy
If Class-G or Class-H amplifier topologies are used to reduce power waste in output transistors, then power efficiency is improved, but magnitude droop in the signal path affects performance and battery life
Solution Approach 1:
The patent implements feedback control by monitoring the magnitude of the output signal and using this information to adjust the gain in both digital and analog signal paths. This feedback mechanism compensates for magnitude droop by dynamically adjusting gain to maintain consistent signal levels across different operating conditions, thereby improving signal path performance while preserving power efficiency.
3Loss of energy
If multiple thresholds define output signal level-dependent operating modes for the charge pump power supply, then power efficiency is improved, but the complexity of the control system increases
Solution Approach 1:
The control circuit is designed to perform multiple functions: it monitors output signal magnitude, determines operating modes based on multiple thresholds, controls both digital and analog gain, and manages charge pump power supply modes. By making the control circuit universal and multi-functional, the patent reduces the need for separate control mechanisms, thereby managing complexity while achieving improved power efficiency through multiple operating modes.
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 enhances dynamic range, reduces noise, and improves power efficiency by compensating for magnitude droop and minimizing charge pump noise impact, leading to improved performance and extended battery life in personal audio devices.
Implementation Method 1
the charge pump is operated at a switching frequency that matches a zero of a modulator noise transfer function to minimize an impact of charge pump noise on a total harmonic distortion noise
Data Source
AI summary
An apparatus for generating an output signal, may comprise a signal path having an analog signal path portion having an analog magnitude droop, a digital signal path portion having a digital magnitude droop, a digital-to-analog converter for converting the digital input signal into the analog signal, a first digital compensation filter that compensates for the analog magnitude droop, and a second digital compensation filter that compensates for the digital magnitude droop, such that the first digital compensation filter and the second digital compensation filter together compensate for magnitude droop of the signal path to ensure a substantially flat passband response of the signal path.An apparatus may include a delta-sigma modulator for quantization noise shaping of a digital signal, a digital-to-analog converter configured to generate an analog signal from the digital signal, and an amplifier configured to amplify the analog signal and powered from a charge pump, wherein the charge pump is configured to operate at a switching frequency approximately equal to a zero of a modulator noise transfer function of the delta-sigma modulator, such that the impact of charge pump noise on a total harmonic distortion noise of the apparatus is minimized.