Multi-Mode Sigma-Delta ADC for Microphone CMR and Power Tradeoffs
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Solution Overview
Problem
Sigma-delta ADCs with single-ended inputs face suboptimal common mode rejection (CMR) performance, particularly in applications with longer wires or adaptive active noise canceling, which increases power consumption and noise interference.
Innovation Solution
A multi-mode sigma-delta ADC circuit that includes operational transconductance amplifiers (OTAs), a filter, a quantizer, and a differential digital-to-analog converter (DAC), with a controller to switch between single-ended, pseudo differential, and full differential operational modes to enhance CMR performance by controlling the OTAs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a single-ended input is used with ground as differential input, then the circuit achieves high integration and low power consumption, but the common mode rejection (CMR) performance is generally not optimal
Solution Approach 1:
The circuit dynamically switches between single-ended and pseudo-differential modes based on operational requirements. The controller enables or disables specific OTAs to reconfigure the input stage, allowing the system to adapt its CMR performance and power consumption characteristics in real-time rather than being fixed in a single configuration
Solution Approach 2:
The same ADC circuit architecture serves multiple functions by operating in different modes. The pseudo-differential mode provides enhanced CMR performance when needed, while the single-ended mode offers lower power consumption for applications where CMR is less critical, making the circuit universally applicable to various audio scenarios
2Reliability
If adaptive active noise canceling (ANC) is implemented with longer wires or cables, then noise cancellation capability is improved, but common mode ripple increases and power consumption increases
Solution Approach 1:
The system dynamically adjusts its operational mode based on the presence and requirements of ANC functionality. When ANC is active and common mode ripple becomes significant, the controller switches to pseudo-differential mode to reject the ripple, thereby managing power consumption adaptively rather than continuously operating at high power levels
3Reliability
If adaptive active noise canceling (ANC) is implemented with longer wires or cables, then noise cancellation capability is improved, but common mode ripple increases
Solution Approach 1:
The circuit converts the harmful common mode ripple generated by ANC and long cables into a manageable signal by using the differential input structure. The ripple appears as a common mode signal that can be rejected by the differential architecture, turning the harmful interference into a rejectable artifact rather than a performance-degrading factor
Data Source
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AI summary
Embodiments of multi-mode sigma-delta analog-to-digital converter (ADC) circuits and a microphone circuit are disclosed. In an embodiment, a multi-mode sigma-delta ADC circuit includes a pair of operational transconductance amplifiers (OTAs), a filter connected to the pair of OTAs, a quantizer connected to the filter, a differential digital-to-analog converter (DAC) connected to the quantizer, and a controller configured to switch the multi-mode sigma-delta ADC circuit between a single-ended operational mode, a pseudo differential operational mode, and a full differential operational mode to improve common mode rejection (CMR) performance by controlling the pair of OTAs. An output of a microphone and a differential output of the differential DAC are inputted into input terminals of the pair of OTAs.