Sigma-Delta ADC Modulator Local Feedback Bandwidth Tuning
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Solution Overview
Problem
Sigma-delta ADC modulators face stability issues due to dynamic quantizer gain changes, which can lead to system instability, especially when the internal signal becomes large, requiring additional circuitry for calibration and increased system complexity.
Innovation Solution
Incorporating local feedback circuits into the loop filter of the sigma-delta ADC modulator, allowing for adjustable feedback coefficients in the feedback weighting amplifiers to tune the bandwidth and maintain stability across varying signal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If local feedback circuits are added to the loop filter, then stability is improved and bandwidth tunability is achieved, but device complexity increases
Solution Approach 1:
The patent introduces local feedback circuits within the loop filter structure, where feedback weighting amplifiers feed back a portion of the output signal to earlier stages. This feedback mechanism stabilizes the system by counteracting the effects of dynamic quantizer gain changes and prevents saturation propagation, thereby improving reliability while maintaining a manageable circuit architecture.
Solution Approach 2:
The patent implements adjustable feedback coefficients in the feedback weighting amplifiers, allowing the feedback strength to be dynamically tuned. This enables bandwidth tunability and adaptive stability control across varying signal conditions, resolving the contradiction by making the system adaptable rather than static, thus improving reliability without permanently increasing complexity.
2Adaptability or versatility
If feedback coefficients are made adjustable, then bandwidth tunability is achieved, but device complexity increases
Solution Approach 1:
The patent changes the feedback coefficient parameter of the feedback weighting amplifiers to achieve bandwidth tuning. By adjusting this single parameter, the system can adapt its frequency response and bandwidth characteristics without requiring complete circuit redesign, thus achieving versatility with minimal complexity increase.
Solution Approach 2:
The adjustable feedback coefficients enable the same loop filter circuit to serve multiple functions: filtering, stability control, and bandwidth adaptation. This multi-functionality reduces the need for separate circuits for each function, thereby achieving versatility without proportionally increasing overall device complexity.
Data Source
AI summary
A high order continuous-time Sigma-Delta Modulator (ΣΔM) is used for its high carrier-to-noise ratio (CNR) performance and low power consumption. The modulator is designed to allow zero-IF, wide-band low-pass or low-IF flexibility. The sigma-delta ADC modulator includes a receiving circuit, a plurality of loop filter transconductors, a plurality of feedforward weighting amplifiers, a first adding element, at least a local feedback circuit, a quantizer, and a feedback DAC. The local feedback circuit includes a feedback weighting amplifier and a second adding element. The feedback coefficient of the feedback weighting amplifier is tunable, and the local feedback circuits can be designed to maximize bandwidth combination.