SAR ADC Non-Binary Search With Binary-Weighted DAC
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Solution Overview
Problem
Designing a non-binary successive approximation analog to digital converter (SA-ADC) with a binary-weighted digital to analog converter (DAC) poses challenges in layout implementation and requires complex logic and routing, especially when using a thermometric DAC.
Innovation Solution
A successive approximation analog to digital converter (SA-ADC) incorporating a binary-weighted DAC, successive approximation register (SAR) logic, and a comparator, which employs a non-binary search algorithm to generate digital codes, allowing for overlapping search windows to correct errors and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a non-binary weighted DAC is used to implement non-binary SA-ADC, then the conversion accuracy is improved, but the layout implementation becomes difficult and complex
Solution Approach 1:
The patent changes the search algorithm parameter from non-binary to binary, while maintaining non-binary conversion accuracy through overlapping search windows. This transforms the difficult non-binary weighted DAC implementation into a simpler binary-weighted DAC implementation that achieves the same conversion accuracy.
Solution Approach 2:
Instead of implementing non-binary weighting directly in the DAC (which is difficult), the patent inverts the approach by using binary-weighted DAC with overlapping binary search windows to achieve non-binary conversion accuracy. This reverses the conventional approach and simplifies the implementation.
2Measurement precision
If a thermometric DAC is used for non-binary search, then the conversion accuracy is improved, but the logic complexity and routing complexity increase
Solution Approach 1:
The patent changes the DAC type parameter from thermometric to binary-weighted, and changes the search algorithm from non-binary to binary with overlapping windows. This reduces logic and routing complexity while maintaining conversion accuracy through the overlapping search window mechanism.
Solution Approach 2:
The patent uses multiple overlapping binary search windows that replicate the search process at different offsets. This copying approach allows the system to achieve non-binary conversion accuracy using simple binary-weighted DAC and binary search logic, avoiding the complexity of thermometric DAC implementation.
3Reliability
If overlapping search windows are used for error correction, then the reliability is improved, but the number of search iterations increases
Solution Approach 1:
The patent uses partial overlapping between search windows, where the overlap is just sufficient to provide error correction capability. This excessive action (using more iterations than minimum binary search) is limited to only the necessary degree, balancing reliability improvement with time efficiency.
Data Source
AI summary
A successive approximation analog to digital converter (SA-ADC) employs a binary-weighted digital to analog converter (DAC) to perform a non-binary search in determining a digital representation of a sample of an analog signal. In an embodiment, a subset of iterations needed to convert an analog sample to a digital value is performed using non-binary search with a radix of conversion less than two. As a result, search windows in iterations corresponding to the non-binary search overlap, and correction of errors due to a comparator used in the SA-ADC is rendered possible. Error correction being possible due to the non-binary search, the comparator is operated in a low-bandwidth, and hence low-power, mode during the non-binary search. The non-binary search in combination with the binary-weighted architecture of the DAC offer several benefits such as for example, less-complex implementation, shorter conversion time, easier and compact layout and lower power consumption.