Orthogonal-Function Calibration for Mixed-Signal Nonlinearity Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-linearity in mixed-signal ICs, particularly in ΔΣ DACs and ΔΣ FN-PLLs, limits their performance by causing noise and distortion, which cannot be effectively removed by simple filters, and existing compensation techniques are inadequate for high-performance applications.
Innovation Solution
An adaptive non-linearity identification and compensation scheme using orthogonal kernels and the Least Mean Square (LMS) method to accurately represent and compensate for non-linearity in circuit blocks, allowing for robust performance across Process, Supply, and Temperature (PVT) variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If multi-bit DAC is used to reduce quantization noise, then bandwidth is improved, but linearity deteriorates due to mismatch between DAC unit cells
Solution Approach 1:
The multi-bit DAC is segmented into multiple unit cells, each contributing to the overall output. By dividing the DAC into smaller functional units, the patent enables independent optimization of each cell while maintaining overall system performance. This segmentation allows the system to achieve high bandwidth through parallel operation while managing linearity through controlled matching requirements of individual cells.
2Manufacturing precision
If segmented DAC architecture is used to improve matching, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent merges the segmentation approach with shared resource utilization. Multiple DAC unit cells share common control logic, timing circuits, and calibration mechanisms, thereby reducing overall device complexity while maintaining the linearity benefits of segmentation. This combining strategy allows the system to achieve improved matching without proportionally increasing complexity.
Solution Approach 2:
The patent employs parameter changes through calibration techniques that adjust operating conditions of DAC unit cells. By dynamically modifying control parameters such as switching timing, reference voltage levels, or cell activation patterns, the system optimizes matching between cells to improve linearity without requiring complex hardware modifications.
3Measurement precision
If non-linearity compensation is implemented, then SNDR and SFDR are improved, but device complexity increases
Solution Approach 1:
The patent implements non-linearity compensation through feedback mechanisms that measure actual DAC output and adjust control signals accordingly. By continuously monitoring performance metrics and applying corrective feedback to DAC unit cells, the system improves SNDR and SFDR while using relatively simple feedback circuits compared to complex pre-compensation architectures.
Solution Approach 2:
The patent enables the DAC system to perform self-calibration and self-correction of non-linearities. Through built-in test modes and automatic calibration routines, the DAC units identify and compensate for their own matching errors without requiring external complex compensation circuits, thereby improving performance while minimizing additional device complexity.
Data Source
AI summary
A feedback divider in a mixed-signal circuit is modulated by a frequency control word controlling a delta-sigma modulator. An accumulated quantization error from the delta-sigma modulator is compared to a residual error in the circuit by a Least-Mean Square (LMS) correlator for gain calibration to adjust for linear errors. Upper bits of the accumulated quantization error access a lookup table to find two outputs of the compensation function that are interpolated between using lower bits of the accumulated quantization error. The interpolated result is an adjustment subtracted from the loop to compensate for non-linear errors. A set of orthogonal kernels is generated from the accumulated quantization error and calibrated using another LMS correlator and inverse transformed to generate updates to the non-linear compensation function in the lookup table. The kernels can be Walsh Hadamard (WH) and the inverse transformer an inverse WH transformer.