Unit-Element Ramp Generator for Linear ADC Conversion
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Solution Overview
Problem
Existing analog-to-digital converters (ADCs) face nonlinearity issues due to charge injection, amplifier offset, and component mismatch, leading to integral non-linearity and gain errors, which are exacerbated by accelerated ramp voltage techniques, making them impractical for modern integrated circuit implementation.
Innovation Solution
The use of rotating unit elements with unique switches and a single reference voltage to generate accelerated ramps, eliminating charge injection errors and allowing for linearly related step sizes, and the implementation of a delta-sigma modulator for fractional gains with a low-pass filter to smooth the ramp signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If accelerated ramp voltage is used to reduce conversion time, then conversion speed is improved, but nonlinearity and integral non-linearity increase due to charge injection and component mismatch
Solution Approach 1:
The ramp generator is divided into multiple segmented ramps, each with a different slope determined by a unique binary-coded weight assigned to each segment. This segmentation allows the system to achieve accelerated conversion by using steeper slopes for larger voltage ranges while maintaining linearity through the weighted combination of segments.
Solution Approach 2:
Each ramp segment is assigned a unique binary-coded weight that determines its specific slope characteristic. This local quality assignment ensures that each segment contributes precisely to the overall transfer function, maintaining linearity while enabling accelerated conversion speeds through the varied slope structure.
2Productivity
If multiple ramp segments with different slopes are used, then conversion time is reduced, but circuit complexity increases due to multiple switches and charge injection errors
Solution Approach 1:
Multiple ramp segments are merged into a unified transfer function through binary-coded weighting. Instead of implementing each segment as a separate physical circuit with independent switches, the invention combines their effects through a systematic weighting scheme that reduces the number of independent control elements while maintaining the accelerated conversion capability.
Solution Approach 2:
The ramp generator structure is designed to serve multiple functions: it provides accelerated conversion through varied slopes, maintains linearity through binary-coded weighting, and reduces charge injection effects through the systematic assignment of unique weights to each segment. This multi-functionality reduces overall circuit complexity while achieving high productivity.
3Measurement precision
If ramp gains for each section are made accurate to minimize integral non-linearity, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The invention changes the parameter representation from requiring precise absolute gain control to using binary-coded relative weighting. Each ramp segment is assigned a unique binary weight that defines its contribution to the overall transfer function. This parameter transformation simplifies the calibration process while maintaining high measurement precision, as the binary weights provide a systematic framework for achieving accurate integral non-linearity performance without complex gain matching.
Data Source
AI summary
A method for generating a ramp comprises providing a voltage reference source, providing a summing amplifier, providing n switched capacitor elements coupled in parallel between the voltage reference source and the summing amplifier, and selectively activating a predetermined number of the switched capacitor elements to first store charge on each activated switched capacitor element and then to measure the sum of the charges on the activated capacitor switch elements in each of a fixed-integer number of time slots in a cyclical manner, the predetermined number being between 0 and n.