Class-D Amplifier Feedforward Compensation for Low-Noise Mode Switching
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Solution Overview
Problem
Conventional class-D amplifiers face performance limitations due to analogue effects in the output driver stage, such as noise and distortion, which are exacerbated by the noise and resolution limitations of analogue-to-digital converters (ADCs) in feedback paths, impacting both power consumption and signal quality.
Innovation Solution
The amplifier circuitry is designed to be selectively operable in open- and closed-loop modes, utilizing a forward signal path, a feedback path, and a feedforward path with a compensation module to maintain a consistent overall transfer function across modes, allowing dynamic switching based on signal amplitude and power supply noise, thereby mitigating noise contributions from ADCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback techniques are used to suppress signal distortion from analogue effects in the output driver stage, then signal quality is improved, but the noise and resolution limitations of the ADC in the feedback path degrade performance
Solution Approach 1:
The patent introduces a digital correction signal as an intermediary that compensates for ADC quantization noise and distortion without requiring the ADC to directly process the full-resolution feedback signal. The correction signal is generated digitally and added to the input signal, acting as a mediator that eliminates the need for high-resolution ADC processing while still achieving distortion suppression.
Solution Approach 2:
The patent replaces the traditional analogue feedback mechanism that relies on high-resolution ADC conversion with a digital-domain correction approach. Instead of using a complex high-resolution ADC system, the invention uses digital signal processing to generate correction signals that substitute for the function of high-resolution analogue-to-digital conversion.
2Measurement precision
If the amplifier operates in closed-loop mode to reduce distortion, then signal quality improves, but power consumption increases due to ADC operation
Solution Approach 1:
The patent applies partial feedback action by using a low-resolution ADC that processes only the most significant bits of the feedback signal, combined with digital correction for the less significant bits. This partial processing approach reduces ADC power consumption while still achieving effective distortion suppression through the combination of analogue feedback and digital correction signals.
Solution Approach 2:
The patent changes the resolution parameter of the ADC from high-resolution to low-resolution, fundamentally altering the operating characteristics of the feedback path. By using a low-resolution ADC and compensating through digital correction signals, the system achieves closed-loop performance with significantly reduced power consumption.
3Measurement precision
If a high-resolution ADC is used in the feedback path to minimize quantization noise, then measurement precision improves, but device complexity and power consumption increase
Solution Approach 1:
The patent uses partial ADC resolution by processing only the most significant bits through the ADC and handling the less significant bits through digital correction. This partial action approach achieves effective high-resolution performance without requiring a physically complex high-resolution ADC.
Solution Approach 2:
The patent fundamentally changes the resolution parameter of the ADC from high to low, and compensates for this parameter change through digital signal processing. The low-resolution ADC operates with fewer bits, reducing complexity, while digital correction signals restore the effective resolution.
Data Source
AI summary
This application relates to amplifier circuitry, in particular class-D amplifiers, operable in open-loop and closed-loop modes. An amplifier (300) has a forward signal path for receiving an input signal (SIN) and outputting an output signal (SOUT) and a feedback path operable to provide a feedback signal (SFB) from the output. A feedforward path provide a feedforward signal (SFF) from the input and a combiner (105) is operable to determine an error signal (ε) based on a difference between the feedback signal and the feedforward signal. The feedforward comprises a compensation module (201) configured to apply a controlled transfer function to the feedforward signal in the closed-loop mode of operation, such that an overall transfer function for the amplifier is substantially the same in the closed-loop mode of operation and the open-loop mode of operation.