Delta-Sigma DAC Mute Circuit Power-Up Glitch
Solution Overview
Problem
Conventional Delta-Sigma DACs face challenges in avoiding power-up glitches, particularly in finite impulse response (FIR) based designs and switched capacitor architectures, due to unpredictable zero patterns and significant loading from operational amplifiers, which can result in audible noise.
Innovation Solution
A Delta-Sigma DAC design that includes an interpolator, Delta-Sigma modulator, FIR filter, and an analog filter with a mute signal mechanism to disable the analog filter during power-up and utilize switches and an operational amplifier with a modified output stage to prevent glitches by coupling the output node to ground when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter enters High-Z mode to block power-up glitches, then power-up glitches are avoided, but the solution cannot be applied to FIR based Delta-Sigma DACs or switched capacitor architectures
Solution Approach 1:
A mute circuit is introduced as an intermediary component between the Delta-Sigma modulator and the output stage. This mute circuit receives a mute signal and selectively connects or disconnects the output node from the signal path, providing a universal solution that works across different Delta-Sigma DAC architectures including FIR-based and switched capacitor designs, replacing the architecture-specific inverter High-Z mode approach
Solution Approach 2:
The output stage is segmented into controllable sections: the mute circuit is separated as an independent functional block with its own control signal, allowing it to be selectively activated or deactivated. This segmentation enables the solution to be adapted to various architectures without requiring modifications to the core Delta-Sigma modulator or other architecture-specific components
2Stability of the object's composition
If zero patterns are output from the Delta-Sigma modulator during initialization, then the modulator converges to stability, but unpredictable duty cycle transients generate audible glitches
Solution Approach 1:
The mute circuit is activated in advance during the modulator's initialization period, blocking the output before the zero pattern transients can reach the output stage. The mute signal is enabled during power-up and remains active until the modulator completes its convergence, preventing the harmful transients from being amplified while allowing the modulator to stabilize
Solution Approach 2:
The zero pattern output, which initially causes harmful glitches, is utilized beneficially by the mute circuit's control logic. The detection of zero patterns triggers the mute circuit to remain active, converting the potentially harmful transient into a useful synchronization signal that coordinates the muting duration with the modulator's initialization phase
3Reliability
If the output switch couples the audible signal to ground to avoid power-up glitches, then power-up glitches are blocked, but the switch may not effectively pull the signal to ground due to significant loading from the operational amplifier
Solution Approach 1:
Instead of directly switching the heavy-loaded audible signal output node to ground, the invention creates a simplified copy version of the switching function in the mute circuit. The mute circuit implements the essential grounding function with reduced complexity, avoiding the need to directly handle the full loading current while achieving the same glitch-blocking effect through the mute signal control path
Data Source
AI summary
A Delta-Sigma DAC is provided, comprising an interpolator, a Delta-Sigma modulator, a FIR filter and an analog filter. The interpolator oversamples a n-bit digital signal to generate a n-bit oversampled signal. The Delta-Sigma modulator coupled to the output of interpolator shapes the n-bit oversampled digital signal to generate a shaped digital signal. The FIR filter coupled to the Delta-Sigma modulator filters the shaped digital signal to generate an analog audio signal. The analog filter coupled to the FIR filter amplifies the analog audio signal to generate a audible signal.