SAR ADC Reference Current Control for Noise-Limited Conversion
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Solution Overview
Problem
Existing successive approximation type A/D conversion circuits face errors due to noise current injected into the reference power supply, leading to impedance shifts and inaccuracies in analog-to-digital conversion.
Innovation Solution
Incorporating current amount control elements and a current control unit that limits noise current to an allowable value by applying a current control potential during the switching of high-order bit switches, thereby reducing noise voltage and error while maintaining conversion speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If noise current is injected into the reference power supply during operation, then the A/D conversion circuit can operate, but a shift of impedance (noise voltage) is generated causing error in conversion
Solution Approach 1:
A current control element is introduced as an intermediary component between the reference power supply and the capacitor. This mediator limits the noise current flowing to the reference power supply while allowing the A/D conversion operation to proceed, thereby reducing the noise voltage that causes conversion errors without significantly affecting conversion speed
Solution Approach 2:
The current control element dynamically adjusts the current parameter flowing to the reference power supply by applying a current control potential. This parameter change limits the noise current to an allowable value, reducing the impedance shift and noise voltage while maintaining necessary operation current
2Measurement precision
If current control element is added to limit noise current, then noise voltage and error are reduced, but device complexity increases
Solution Approach 1:
The current control element is applied locally only to the reference power supply connection where noise current causes problems, rather than controlling all current paths in the circuit. This targeted approach reduces noise voltage with minimal additional complexity, as only one specific location requires the control mechanism
3Measurement precision
If current control potential is applied during switching of high-order bit switches, then noise current is limited, but conversion time may be affected
Solution Approach 1:
The current control potential is applied periodically or selectively during specific switching operations (high-order bit switches) rather than continuously. This timed application limits noise current during critical switching moments while minimizing impact on overall conversion time by not restricting current flow during non-critical periods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces noise voltage and error in A/D conversion while minimizing the impact on conversion time, providing a faster and more accurate conversion process compared to conventional technologies.
Implementation Method 1
capacitors C1 to C4 whose capacitance values are weighted to 2nC, such as 1 C, 2 C, and 4 C; A charge resulting from the difference between the input potential and the comparison potential is stored in the capacitors C4, C3, C2, and C1
Implementation Method 2
current amount control element; a current amount control unit that controls current amount flowing to the current amount control element in each bit circuit of the bit circuits
Data Source
AI summary
An analog-digital conversion circuit is disclosed for comparing a comparison potential with a reference potential generated based on a reference power supply to convert a comparison potential to a digital value. An analog-to-digital converter generates the comparison potential based on a sampled and held input potential, the digital value, and the reference power supply. A current amount control unit controls current amount flowing to the current amount control element in each bit circuit. In response to second switches of the bit circuits being turned on in order from the upper bit in each bit circuit by the digital value, the current amount control unit applies a current control potential to the current amount control element in any of the bit circuits that the noise current is more than allowable value while the noise current proportional to the charge flowing from the capacitor is more than the allowable value.