Segmented DAC Architecture for Digital to Analog Conversion
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Solution Overview
Problem
Existing digital to analog conversion techniques face inaccuracies due to current source mismatches and require hardware filters, limiting their efficiency in terms of speed and accuracy.
Innovation Solution
The method employs equal output signal magnitude sources, such as current or voltage sources, for multi-bit delta-sigma modulation, followed by a finite impulse response (FIR) filter, with dynamic selection logic to optimize resolution, accuracy, and bandwidth on a per signal basis, and uses a segmented DAC for over-sampling, allowing software programmable tradeoffs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If current steering Nyquist DAC with binary weighted current sources is used, then conversion speed is improved, but output signal accuracy deteriorates due to current source mismatch
Solution Approach 1:
The DAC is divided into two independent segments: a Nyquist DAC for high-speed conversion of less significant bits and a Delta-Sigma DAC for high-precision conversion of more significant bits. This segmentation allows each segment to be optimized for its specific function, resolving the contradiction between speed and accuracy.
Solution Approach 2:
Different parts of the signal are processed with different qualities: the less significant bits are converted with high speed using binary weighted current sources, while the more significant bits are converted with high precision using equal current sources and dynamic element matching. Each part receives the appropriate quality treatment for its requirements.
2Measurement precision
If Delta-Sigma converter with equal current sources is used, then conversion accuracy is improved, but conversion speed deteriorates
Solution Approach 1:
The Delta-Sigma converter segment is dedicated to converting only the more significant bits with high precision, while the Nyquist DAC segment handles the less significant bits at high speed. This segmentation allows the Delta-Sigma portion to focus on accuracy without being constrained by speed requirements.
Solution Approach 2:
The system uses more equal current sources than strictly necessary for the resolution required, applying dynamic element matching with a larger pool of sources than minimally needed. This excessive action provides a larger margin for error averaging, further improving accuracy beyond what would be achieved with minimal sources.
3Measurement precision
If hardware filter is added to suppress harmonic content, then output signal quality is improved, but device complexity increases
Solution Approach 1:
The patent replaces the traditional mechanical/analog hardware filter with a digital signal processing approach using dynamic element matching and selective signal processing. The filtering and harmonic suppression functions are achieved through digital algorithms and switching networks rather than passive analog filter components.
Solution Approach 2:
The dynamic element matching unit acts as an intermediary between the digital input and the current sources, providing both dithering and implicit filtering functions. This intermediary structure achieves signal quality improvement without requiring a separate hardware filter stage.
4Measurement precision
If dynamic element matching with subset selection is used, then accuracy is improved by averaging mismatch errors, but device complexity increases
Solution Approach 1:
The dynamic element matching unit performs multiple functions simultaneously: it provides dithering to linearize the transfer function, implements dynamic selection to average out mismatch errors, and acts as a form of digital filtering. This multi-functionality reduces the need for separate complexity-inducing components.
Solution Approach 2:
The system uses dynamic switching and time-varying selection of current sources rather than static assignments. The switching network dynamically reconfigures which current sources are active based on the input code and dither signals, providing accuracy improvement through temporal averaging rather than requiring more physical components.
Data Source
AI summary
A method and a corresponding system for converting a digital signal to an analog signal using a plurality of signal sources, preferably current sources, at least two of the signal sources being equal output signal magnitude sources, said method including controlling the equal output signal magnitude sources by a logic circuit, providing a digital input signal to the logic circuit, the digital input signal being derived from the digital signal to be converted, filtering the digital input signal using a filter, the filter having a filter order being adaptable by the logic unit in response to needs concerning bandwidth of the conversion, and summing the outputs of the equal output signal magnitude sources to contribute to the analog signal.