Slope ADC Nonlinear Counter Mapping for Linear Conversion
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Solution Overview
Problem
Slope analog-to-digital converters (ADCs) face challenges in accurately converting analog input signals to digital representations over the entire range of possible values due to nonlinearities introduced by processing stages, such as input buffers and sampling networks, leading to errors that require digital post-processing to correct.
Innovation Solution
A slope ADC with a nonlinear relationship between the slope signal and the counter signal is employed to compensate for these nonlinearities, ensuring accurate conversion of both small and large input values without the need for digital post-processing, by adapting the transfer function to be closer to linear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional slope ADC with linear relationship between slope signal and counter signal is used, then the device complexity is low, but the measurement precision deteriorates due to nonlinearities in processing stages
Solution Approach 1:
The patent changes the relationship parameter between slope signal and counter signal from linear to nonlinear. Specifically, the counter signal is designed to increment at varying rates depending on the slope signal level, creating a nonlinear mapping that compensates for processing nonlinearities. This parameter transformation enables accurate conversion across the entire analog input range without requiring complex digital post-processing correction circuits.
2Measurement precision
If digital post-processing is added to correct nonlinearities, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-compensating for nonlinearities in the analog domain before digital conversion. The nonlinear relationship between slope signal and counter signal is designed in advance to counteract expected nonlinearities from input buffers and sampling networks. This eliminates the need for subsequent digital post-processing correction, thereby maintaining high conversion accuracy while avoiding additional processing complexity.
3Measurement precision
If the transfer function is made nonlinear to compensate for processing nonlinearities, then the measurement precision improves, but the ease of operation deteriorates due to difficulty in understanding and implementing the nonlinear relationship
Solution Approach 1:
The patent introduces an intermediary nonlinear transformation stage between the linear slope signal and the counter signal. This intermediary function serves as a bridge that converts the simple linear slope signal into a counter signal with appropriate nonlinear characteristics. The intermediary transformation can be implemented using standard analog circuits such as lookup tables or polynomial generation circuits, making the implementation straightforward despite the nonlinear relationship.
Data Source
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AI summary
A slope analog-to-digital converter, ADC, (100) for converting an analog input signal to a digital representation, said slope ADC (100) comprising: a comparator (120) configured to compare two input signals, wherein a sampled value of the analog input signal and a slope signal are used in forming the two input signals; a memory element (130), which is configured to receive a trigger signal based on the comparator (120) identifying a change in which of the two input signals is higher, and a counter signal, wherein a value of the counter signal when the trigger signal is received provides the digital representation of the sampled value of the analog input signal; wherein the slope signal and the counter signal have a nonlinear relationship, wherein the nonlinear relationship is adapted to improve linearity of a transfer function of the slope ADC (100) for converting the analog input signal to the digital representation.