Auto-Biased Current Comparator for Fast DAC Calibration
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Solution Overview
Problem
Existing digital to analogue converters require accurate current comparators for calibration to compensate for current source mismatches, but existing solutions are limited by feedback loops and charge injection, affecting accuracy and speed.
Innovation Solution
A current comparator circuit with an auto-biasing scheme and a switch mechanism that allows for a common mode current detection without a feedback loop, enabling fast and accurate calibration of current sources by automatically adjusting biasing and using a high gain comparator to discriminate low current differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback loop is used in the current comparator circuit, then the accuracy of current comparison can be improved, but the speed of calibration is reduced and the circuit becomes more complex
Solution Approach 1:
The patent removes the feedback loop from the current comparator circuit, extracting the problematic element that caused the contradiction. By eliminating the feedback mechanism, the circuit achieves fast calibration speed without sacrificing accuracy, as the auto-biasing scheme provides the necessary stability without the speed penalty of feedback loops.
Solution Approach 2:
The current comparator circuit uses an auto-biasing scheme where the circuit automatically adjusts its own biasing conditions without external feedback. This self-service mechanism allows the circuit to maintain accuracy while operating at high speed, as each current conveyor automatically establishes its operating point based on the input currents.
2Measurement precision
If a feedback loop is used in the current comparator circuit, then the accuracy of current comparison can be improved, but the circuit complexity increases
Solution Approach 1:
The patent extracts and removes the feedback loop component from the circuit, thereby reducing circuit complexity while maintaining accuracy through the auto-biasing mechanism implemented by the current conveyors.
Solution Approach 2:
The circuit achieves accuracy without external feedback by implementing self-service auto-biasing within the current conveyor blocks, eliminating the need for complex feedback networks while maintaining precise current comparison capability.
3Reliability
If reset switches are used in the current comparator circuit, then the circuit can be reset to a known state, but charge injection affects the accuracy of current measurement
Solution Approach 1:
The patent acknowledges the charge injection from reset switches as an unavoidable phenomenon but converts its harmful effect into a benefit by designing the auto-biasing scheme to automatically compensate for and cancel the charge injection effects, thereby maintaining measurement accuracy while preserving reset capability.
Data Source
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AI summary
A current comparator circuit and method. The circuit includes a first input and a second input to receive currents I1, and I2. The circuit includes a current-to-voltage converter and a switch. The circuit includes a first and second current branches comprising a current input terminals coupled to the first input and the second input. In a first mode the switch is closed to cause an input voltage at the first input and at the second input to be equal. In a second mode the switch is opened whereby a current flows through the current-to-voltage converter and voltage ΔV appears across the first input and the second input. In both the first mode and the second mode, the current flowing through the first branch and the current flowing through the second branch are equal to (I1 + I2)/2.