Switched-Capacitor Amplifier Delay Compensation for Faster ADCs
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Solution Overview
Problem
Comparator-based switched-capacitor amplifiers face challenges in operating speed and accuracy due to variations in manufacturing processes, supply voltage, and temperature, which affect the conversion speed and accuracy of pipelined analog-to-digital converters.
Innovation Solution
A comparator-based switched-capacitor amplifier with a closed loop control circuit that dynamically compensates for comparator delay and offset, using a time-to-digital converter to determine and adjust the comparator offset, thereby reducing signal overshoot and making the amplification process independent of PVT variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a comparator-based switched-capacitor amplifier uses a coarse current source to discharge the sample capacitor and a fine current source to recharge it, then the error due to charge overshoot caused by comparator delay is reduced, but the recharge phase takes a considerably long time which slows down the operation
Solution Approach 1:
The patent applies dynamics by making the current source adjustable between coarse and fine modes. The current source can dynamically switch between high current (coarse) for fast discharge and low current (fine) for precise recharge, optimizing both speed and precision at different phases of operation.
Solution Approach 2:
The patent uses periodic action by alternating between coarse discharge phase and fine recharge phase. The controller switches between two current source modes in a periodic manner, using coarse current for discharge and fine current for recharge, thereby achieving both speed and precision through time-division multiplexing.
2Productivity
If the amplifier operates faster to increase ADC conversion speed, then the productivity is improved, but the accuracy is affected by PVT variations which worsens the measurement precision
Solution Approach 1:
The patent implements feedback by using the comparator output to control the switching between coarse and fine current modes. The comparator detects when the virtual ground node approaches the reference voltage, and this feedback signal triggers the switch from coarse discharge to fine recharge mode, ensuring accurate operation at high speed.
Solution Approach 2:
The patent applies parameter changes by varying the current source magnitude based on operational phase. The current source parameter is dynamically changed from high current during discharge to low current during recharge, allowing the system to maintain accuracy while operating at high conversion speeds.
3Measurement precision
If calibration is performed to compensate for PVT variations, then the accuracy is improved, but the process becomes time-consuming and costly which increases the loss of time
Solution Approach 1:
The patent applies self-service by making the amplifier automatically compensate for PVT variations through its inherent switched-capacitor architecture and controller. The system self-adjusts between coarse and fine current modes based on real-time comparator feedback, eliminating the need for external calibration processes while maintaining high accuracy.
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 significantly increases the operating speed and accuracy of the amplifier, reducing the need for calibration and maintaining robustness against PVT variations, while being scalable for use in larger systems.
Implementation Method 1
A sample capacitor is coupled to one of the input terminals through a switch. An amplification capacitor is also coupled to the input terminal of the comparator
Implementation Method 2
A current source is also connected to the input terminal of the comparator and to a current source to charge the sample capacitor through corresponding switches
Data Source
AI summary
A switched-capacitor amplifier comprises a comparator, sample and amplification capacitors and a controller to control charge and discharge current sources in dependence on an output signal of the comparator. A closed loop control circuit is configured to determine the delay of the comparator and control an offset of the comparator in response to the determined delay.