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 flexible, high-gain design that automatically sets a common mode current, allowing for accurate and fast calibration without a feedback loop, using current conveyors and a switch to short or pass current through a current-to-voltage converter.
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 false detections may occur due to charge injection
Solution Approach 1:
The patent removes the feedback loop from the current comparator circuit, extracting the problematic element that caused both charge injection and false detections. By using a direct comparison architecture without feedback, the circuit achieves both high accuracy and fast calibration speed simultaneously, resolving the contradiction between measurement precision and speed.
2Measurement precision
If the current comparator circuit is designed for high accuracy, then the calibration precision of current sources is improved, but the circuit complexity increases
Solution Approach 1:
The current comparator circuit uses an auto-biasing scheme where the circuit automatically sets its own common mode current without requiring external feedback or complex control mechanisms. This self-service approach simplifies the circuit architecture while maintaining high calibration precision, as the comparator inherently stabilizes its operating point through its own internal dynamics.
3Productivity
If a switch is added to control the current path in the comparator circuit, then the flexibility and speed of operation are improved, but the risk of charge injection and false detections increases
Solution Approach 1:
The patent introduces a current-to-voltage converter as an intermediary element that transforms the current comparison into a voltage signal. This intermediary conversion allows the use of switches for fast operation while the voltage domain processing avoids the charge injection problems that would directly affect current measurements, thereby maintaining both speed and reliability.
Data Source
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 AV 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.