Sigma-Delta Modulator Feedforward Impedance Correction for PVT Drift
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Solution Overview
Problem
Sigma-delta modulators (SDMs) are susceptible to process, voltage, and temperature (PVT) variations, leading to resolution degradation and errors, making it challenging to maintain the originally designed signal transfer function (STF).
Innovation Solution
A correction method and circuit that generates a test signal, adjusts impedance circuits within a feedforward circuit, and calculates the signal transfer function (STF) to mitigate the effects of PVT variations by adjusting the impedance circuits to meet the design criteria.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the SDM operates without correction, then the device complexity is low, but the manufacturing precision and reliability deteriorate due to PVT variations
Solution Approach 1:
The patent applies preliminary action by performing STF measurement and impedance circuit adjustment during the manufacturing process or before normal operation. The correction circuit pre-adjusts the impedance circuits based on measured STF values to compensate for PVT variations, ensuring the SDM meets design criteria before being deployed, thus improving manufacturing precision without adding operational complexity.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the impedance of the feedforward circuits based on measured STF values. The correction circuit modifies the impedance parameters of the feedforward circuits to compensate for deviations caused by PVT variations, thereby correcting the STF accuracy while managing device complexity through targeted parameter adjustment rather than complete system redesign.
2Reliability
If the SDM operates without correction, then the device complexity is low, but the reliability deteriorates due to resolution degradation and errors
Solution Approach 1:
The patent implements feedback by measuring the actual STF values of the SDM and using this information to adjust the impedance circuits in the feedforward circuits. The correction circuit continuously monitors STF performance and applies compensatory adjustments, creating a closed-loop system that improves reliability by ensuring the SDM operates according to design specifications despite PVT variations.
Solution Approach 2:
The correction is performed preliminarily during manufacturing or before operation, ensuring the SDM is pre-configured to meet reliability requirements. This preliminary adjustment establishes the correct operating parameters before the SDM encounters PVT variations during normal operation, thereby improving reliability without requiring complex real-time correction mechanisms.
3Manufacturing precision
If the NTF is adjusted for frequency band of interest, then the manufacturing precision improves, but the device complexity increases due to additional correction components
Solution Approach 1:
The patent applies local quality by focusing the correction effort specifically on the frequency band of interest rather than attempting to correct the entire frequency spectrum. The impedance circuits are adjusted to optimize STF performance only where needed, improving manufacturing precision for critical frequencies while minimizing the addition of correction components and overall device complexity.
Data Source
AI summary
A correction method and a correction circuit for a sigma-delta modulator (SDM) are provided. The SDM includes a loop filter, a quantizer, and a digital-to-analog converter (DAC). The correction method includes: generating a test signal for a frequency to be tested; inputting the test signal to a feedforward circuit that includes at least one adjustable impedance circuit, the test signal being inputted to the SDM through the impedance circuit; calculating an output signal of the SDM to obtain a value of a signal transfer function (STF) of the SDM at the frequency to be tested; and adjusting the impedance circuit.