Differential Sigma-Delta Amplifier Noise Correlation for Low-Impedance Loads
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Solution Overview
Problem
Amplifier circuits driving low impedance loads, such as piezo transducers, face high power dissipation due to the folding back of out-of-band noise, which is undesirable especially in portable battery-powered devices.
Innovation Solution
The introduction of a correlation controller in the amplifier circuit, which uses sigma-delta modulators and cross-coupling or common dither signals to correlate noise components between the driving signals, reducing differential power dissipation across the load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single sigma-delta modulator is used to generate differential driving signals for a BTL amplifier, then the circuit complexity is reduced, but out-of-band noise folds back into the signal band causing high power dissipation when driving low impedance loads
Solution Approach 1:
The single modulator is segmented into two separate sigma-delta modulators, one for each output channel. This segmentation allows independent noise shaping in each channel while enabling correlation control between channels, thereby reducing folded-back noise power dissipation in low impedance loads.
Solution Approach 2:
A correlation controller is introduced that provides feedback between the two modulator channels. This feedback mechanism correlates the quantization noise in both channels, ensuring that differential noise components are minimized and folded-back noise power is reduced when driving low impedance loads.
2Loss of energy
If the amplifier circuit is designed to prevent folding back of out-of-band power, then power dissipation is reduced, but power and bandwidth requirements of the amplifier circuit increase
Solution Approach 1:
The quantization noise that would normally fold back and cause power dissipation is converted into a beneficial correlated signal. The correlation controller uses feedback to ensure noise components are correlated between channels, transforming harmful differential noise into useful common-mode signals that do not dissipate power in the load.
Solution Approach 2:
The noise transfer function of the modulator is changed by introducing correlation control. This parameter change in the noise characteristics ensures that out-of-band noise is shaped differently, reducing the folded-back noise power and allowing the amplifier to operate efficiently with lower power requirements.
3Loss of energy
If noise components are correlated between differential signals, then power dissipation is reduced, but the amplifier circuit complexity increases due to additional correlation control mechanisms
Solution Approach 1:
The correlation control function is merged with the existing feedback mechanisms in the sigma-delta modulators. The correlation controller integrates noise shaping and correlation control in a unified structure, reducing overall circuit complexity while achieving the goal of correlated noise components and reduced power dissipation.
Data Source
AI summary
The application describes method and apparatus for amplification. An amplifier circuit (300) is described for driving a load (101) connected between first and second output nodes (103p, 103n) based on an input signal (Sin). The amplifier circuit includes first and second signal paths for generating respective first and second driving signals (Soutp and Soutn) at the first and second output nodes, each of the first and second signal paths comprising a respective sigma-delta modulator (301p, 301n). A correlation controller (302) is configured to control the first and second signal paths to provide correlation between at least some noise components of the first and second driving signals.