Charge Pump Frequency Tuning for Low-Noise Delta-Sigma Audio Paths
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Solution Overview
Problem
Charge pumps in personal audio devices face inefficiencies due to noise-induced issues and magnitude droop in signal paths, which affect dynamic range and battery life, particularly during low signal levels.
Innovation Solution
The implementation of a signal path with digital compensation filters to address magnitude droop, a delta-sigma modulator for noise shaping, and a charge pump operating at a frequency matching the modulator's noise transfer function to minimize harmonic distortion noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
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 patent applies dynamics by making the gain of the power amplifier variable rather than fixed. The amplifier operates at high gain only when necessary (for low-level signals) and switches to low gain for high-level signals. This dynamic adjustment of the gain state resolves the contradiction by allowing high dynamic range when needed while minimizing noise for louder signals.
Solution Approach 2:
The patent implements periodic action through the use of a charge pump that switches between different operating states at a specific frequency. The charge pump periodically adjusts the supply voltage to the power amplifier, enabling the amplifier to alternate between high-gain and low-gain modes. This periodic switching allows the system to optimize between dynamic range and noise performance based on signal requirements.
2Use of energy by moving object
If a charge pump is used to provide variable power supply voltage to reduce power consumption, then power efficiency is improved, but noise from the charge pump increases and affects the audio signal
Solution Approach 1:
The patent converts the harmful charge pump noise into a beneficial effect by intentionally designing the noise transfer function to have a zero at the charge pump switching frequency. This causes the charge pump noise to be attenuated rather than amplified, transforming what would be a harmful interference into a neutral or beneficial element that maintains power efficiency while suppressing noise.
Solution Approach 2:
The patent applies parameter changes by modifying the noise transfer function parameters of the power amplifier circuit. Specifically, the feedback network is designed with specific component values that create a zero in the noise transfer function at the charge pump frequency. This parameter optimization allows the system to maintain high power efficiency while minimizing the impact of charge pump noise on the audio signal.
3Loss of energy
If Class-G or Class-H amplifier topologies are used to reduce voltage drop and power dissipation, then power efficiency is improved, but noise control becomes more challenging due to variable supply voltage
Solution Approach 1:
The patent applies feedback by incorporating a feedback network that includes specific impedance elements designed to create a zero in the noise transfer function. The feedback mechanism continuously monitors and adjusts the amplifier operation to maintain optimal noise performance despite the variable supply voltage conditions created by the Class-G or Class-H topology. This feedback control enables simultaneous achievement of low power dissipation and noise control.
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 ensures a substantially flat passband response, reduces noise, and enhances power efficiency by compensating for magnitude droop and optimizing charge pump noise impact, thereby improving dynamic range and battery life in personal audio devices.
Implementation Method 1
a delta-sigma modulator for noise shaping
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