Sigma-Delta Modulator Feedback Node Compensation for Excess Loop Delay
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Solution Overview
Problem
Continuous-time sigma-delta modulators are sensitive to excess loop delays, which cause instability and require additional components for compensation, leading to increased area and power consumption, and potential degradation of loop stability.
Innovation Solution
A sigma-delta modulator with a multi-stage loop filter and a digital-to-analog converter that provides a compensation signal to internal nodes in the feedback network of the last stage, introducing a constant term to the transfer function to compensate for excess loop delay without affecting stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If excess loop delay compensation is applied through additional feedback digital-to-analog converters, then the stability of the continuous-time sigma-delta modulator is improved, but the area and power consumption increase
Solution Approach 1:
The patent combines the excess loop delay compensation function with the existing feedback digital-to-analog converter by adding a parallel compensation path. Instead of using separate additional converters, the invention merges the compensation functionality into the existing converter structure, using the same hardware resources to achieve both feedback and delay compensation functions simultaneously.
Solution Approach 2:
The patent segments the feedback signal into two parallel paths: one for the main feedback function and another for excess loop delay compensation. By dividing the compensation function into a separate parallel path with its own digital-to-analog converter, the system can independently adjust compensation strength without affecting the main feedback path, thereby improving stability while controlling area usage.
2Reliability
If excess loop delay compensation is applied through additional feedback digital-to-analog converters, then the stability of the continuous-time sigma-delta modulator is improved, but the power consumption increases
Solution Approach 1:
The patent combines the excess loop delay compensation function with the existing feedback digital-to-analog converter. By sharing hardware resources and using the same converter infrastructure for both feedback and compensation functions, the invention reduces the number of additional power-consuming components needed while maintaining stability improvement.
3Reliability
If the delay compensation position is located before the quantizer, then the excess loop delay is compensated, but an additional pole is induced that degrades the loop stability
Solution Approach 1:
The patent applies delay compensation at a specific location in the feedback path rather than uniformly across all paths. By placing the compensation specifically in the feedback path after the quantizer and selecting particular internal nodes for compensation signal injection, the invention achieves localized compensation that avoids introducing harmful additional poles while still correcting excess loop delay effects.
4Reliability
If the delay compensation position is at two input terminals of an operational amplifier, then the excess loop delay is compensated, but the transfer function is changed which is disadvantageous to circuit designs
Solution Approach 1:
The patent carefully selects specific internal nodes within the feedback network where compensation signals are applied, rather than applying compensation at the operational amplifier input terminals. This localized application of compensation at strategically chosen nodes allows the invention to correct excess loop delay while preserving the original transfer function characteristics, avoiding the complexity issues associated with changing the overall transfer function.
Data Source
AI summary
A sigma-delta modulator is provided for generating a digital output signal. The sigma-delta modulator includes a multi-stage loop filter, a quantizer, and a digital-to-analog converter. The multi-stage loop filter receives an analog input signal and generates an integrated output signal according to the analog input signal. Each stage of the multi-stage loop filter includes a feedback network. The quantizer receives the integrated output signal and quantizes the integrated output signal to generate the digital output signal. The digital-to-analog converter receives the digital output signal and converts the digital output signal to a compensation signal. The digital-to-analog converter provides the compensation signal to a plurality of internal nodes in the feedback network of the last stage of the multi-stage loop filter.