MDAC Differential Current Cancellation for Stable Reference Voltage
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Solution Overview
Problem
In analog-to-digital converters, especially in pipeline ADC applications, the settling of reference voltage is challenged by undesired current flow from residue amplifiers into reference voltage sources, leading to errors and nonlinearity, which affects conversion accuracy and power consumption.
Innovation Solution
Implementing current cancellation by injecting a compensating current of the same magnitude into the reference voltage source to neutralize the charging current from the residue amplifier, thereby preventing erroneous charging and improving linearity and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If residue amplifier simultaneously amplifies the difference signal and generates residue voltage, then quantization function is distributed among multiple stages, but charging current flows into reference voltage source causing settling errors
Solution Approach 1:
A compensating current source is introduced as an intermediary element that generates a current equal and opposite to the charging current flowing into the reference voltage source. This mediator cancels the harmful current while allowing the residue amplifier to simultaneously perform amplification and residue generation, maintaining both speed and accuracy.
Solution Approach 2:
The harmful charging current that flows into the reference voltage source during residue amplification is converted into a beneficial effect by generating an equal and opposite compensating current. This transforms the harmful current injection into a useful cancellation mechanism that actually improves reference voltage settling by eliminating the erroneous charging current.
2Measurement precision
If reference voltage is settled to precise voltage level, then conversion accuracy is improved, but settling time increases and power consumption increases
Solution Approach 1:
The compensating current source is activated in advance to counteract the charging current before it can cause significant settling errors. By applying the opposite current proactively during the amplification process, the reference voltage reaches its precise level faster, reducing settling time while maintaining conversion accuracy.
Solution Approach 2:
The compensating current is continuously applied throughout the residue amplification process, ensuring that the reference voltage settles accurately without interruption. This continuous cancellation action maintains precise conversion accuracy while reducing the overall settling time compared to traditional sequential approaches.
3Measurement precision
If compensating current is injected to cancel charging current, then reference voltage settling accuracy is improved, but device complexity increases
Solution Approach 1:
The compensating current source is merged with the existing residue amplifier circuitry, sharing common components such as the operational amplifier and feedback network. This integration reduces device complexity by eliminating redundant elements while maintaining the current cancellation function for improved reference voltage settling accuracy.
Solution Approach 2:
The residue amplifier is designed to perform multiple functions simultaneously: signal amplification, residue generation, and current compensation. By making the amplifier universal and capable of handling all these tasks, the need for separate dedicated compensation circuits is eliminated, reducing overall device complexity while maintaining high settling accuracy.
Data Source
AI summary
Various embodiments of the invention provide for cancellation of a residue amplifier output charging current at the reference voltage source of the reference buffer thereby preventing the charging current from altering the effective reference voltage of a reference buffer. In certain embodiments, current cancellation is accomplished by subtracting a current of the same magnitude.