Single-Ended DAC Gain Control for Pop and Click Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Digital-to-analog converters (DACs) with single-end outputs suffer from transient noise issues, such as 'pop' or 'click', when powered on or off due to rapid changes in the blocking capacitor, leading to annoying sounds in audio applications.
Innovation Solution
The implementation of a digital-to-analog converter system comprising a preprocessing unit, a gain controller, a modulator, and an output unit, which oversamples the digital signal, applies a gain function to gradually adjust the analog signal during power on/off conditions, using noise shaping and modulation techniques to minimize transient noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blocking capacitor is employed in a single-end output DAC to block DC voltage, then the DC blocking function is achieved, but large transient signals appear at the outputs when initially powered on causing pop or click noise
Solution Approach 1:
The patent applies preliminary action by pre-charging the blocking capacitor to the signal ground level (1/2 VDD) before the DAC output is connected to the load. This is achieved through a dedicated pre-charge circuit that activates before normal operation, ensuring the capacitor is already at the correct voltage level when the DAC starts operating, thereby preventing the transient pop or click noise that would otherwise occur during power-on.
Solution Approach 2:
The patent implements preliminary anti-action by using a pre-charge circuit that actively counteracts the potential transient signal before it can occur. The pre-charge circuit applies a voltage opposite to what would cause the transient (by charging the capacitor to the signal ground level in advance), thus preventing the harmful pop or click noise from occurring during power-on or power-off transitions.
2Reliability
If power is removed from the DAC while the blocking capacitor holds charge, then the power-off state is achieved, but the residual charge discharges rapidly across the load resulting in loud noise
Solution Approach 1:
The patent uses an intermediary approach by introducing a pre-charge circuit that acts as a mediator between the blocking capacitor and the load. This circuit provides a controlled path for charge transfer and maintains the capacitor at the signal ground level even during power-off transitions, preventing the rapid uncontrolled discharge that would otherwise occur directly across the load and cause loud noise.
Solution Approach 2:
The patent applies preliminary action by maintaining the blocking capacitor charge at the signal ground level through the pre-charge circuit before power-off occurs. This pre-established charge state ensures that when power is removed, there is no potential difference driving a rapid discharge current through the load, thereby preventing the discharge noise problem.
3Reliability
If the analog output is centered on signal ground level (1/2 VDD), then proper DC blocking is achieved, but the transient signal from ground to signal ground level creates audible noise
Solution Approach 1:
The patent applies preliminary action by pre-charging the blocking capacitor to the signal ground level (1/2 VDD) before the DAC begins normal operation or before power transitions occur. This ensures that when the analog output needs to transition from ground to signal ground level, the capacitor is already at the correct voltage, eliminating the transient step change that would otherwise create audible pop or click noise.
Data Source
AI summary
A digital-to-analog converter for converting a digital signal into an analog signal is provided. The digital-to-analog converter includes a preprocessing unit, a gain controller, a modulator and an output unit. The preprocessing unit receives and oversamples the digital signal to generate an oversampled signal. The gain controller generates an adjusted signal with a gain function according to a reference signal associated with the oversampled signal when a specific condition is present. The modulator modulates the adjusted signal and generates a modulated signal. The output unit provides the analog signal to a load according to the modulated signal, wherein the analog signal gradually approaches to a specific level according to the gain function when the specific condition is present.