ADC Charge-Based Capacitance Measurement for Tiny Internal Capacitors
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Solution Overview
Problem
Integrated circuit designers face challenges in accurately characterizing and measuring the capacitance of small capacitors within analog-to-digital converters (ADCs), particularly due to their sensitivity to nearby features and the difficulty in accessing and measuring them directly.
Innovation Solution
A built-in charge-based capacitance measurement (CBCM) system is integrated into the ADC, utilizing a timing generator, switches, and measurement logic to alternately charge and discharge capacitors, allowing for direct current measurement to determine capacitance without invasive methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional external measurement methods are used for capacitor characterization, then accessibility for measurement is improved, but measurement precision deteriorates due to sensitivity to nearby features and invasive access requirements
Solution Approach 1:
The ADC performs self-diagnosis by integrating capacitance measurement functionality directly into its internal structure. The ADC uses its own operational phases and internal nodes to measure capacitor characteristics without requiring external measurement equipment, thereby eliminating accessibility issues while maintaining high measurement precision through built-in charge-based measurement circuits
Solution Approach 2:
The measurement functionality is nested within the ADC structure itself. The capacitance measurement circuit is integrated into the existing ADC architecture, utilizing internal nodes and operational phases. This nested approach allows measurement capabilities to be embedded deep within the device without adding external measurement interfaces, resolving the contradiction between accessibility and precision
2Measurement precision
If built-in measurement circuits are integrated into the ADC, then measurement precision is improved through direct internal measurement, but device complexity increases due to additional integrated components
Solution Approach 1:
The ADC's existing operational phases and internal nodes are made multi-functional. The same switches, capacitors, and operational phases used for normal ADC conversion are also utilized for capacitance measurement. This universal approach allows the measurement function to be added without requiring dedicated measurement-specific components, thereby minimizing the increase in device complexity while achieving high measurement precision
Solution Approach 2:
The capacitance measurement function is merged with the ADC's normal operational sequence. The measurement operations are combined with the existing sampling and conversion phases, sharing common circuit elements such as switches, capacitors, and control logic. This merging eliminates the need for separate measurement circuitry, reducing the overall complexity increase while maintaining high measurement accuracy
3Adaptability or versatility
If multiple clock signals and control circuits are added for capacitance measurement, then measurement functionality is improved, but productivity deteriorates due to increased testing time and complexity
Solution Approach 1:
The capacitance measurement is performed using periodic clock signals that are already present in the ADC's normal operation. The measurement utilizes the existing periodic sampling and conversion phases of the ADC, repurposing these regular operational cycles for measurement purposes. This approach enables capacitance measurement capability without adding extra testing time, as the measurements are embedded within the existing periodic operational framework
Solution Approach 2:
The measurement operations continue to use the ADC's existing operational phases without interrupting or pausing the normal conversion process. The capacitance measurement is performed continuously during the ADC's regular sampling and conversion cycles, utilizing the same clock signals and control mechanisms. This continuous use of existing useful actions maintains high productivity while adding measurement versatility
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
Enables high-accuracy capacitance measurement of capacitors down to sub-femtoFarad levels with minimal impact on ADC performance, facilitating characterization and calibration of capacitors before and after mass production.
Implementation Method 1
measurement logic including a current sensor to measure a current through the common node and configured to determine a capacitance of the selected capacitor
Implementation Method 2
a plurality of capacitors coupled in parallel to an input voltage at a common node
Data Source
AI summary
An ADC with built-in charge-based capacitance measurements is described. An example includes a plurality of capacitors coupled in parallel to an input voltage at a common node, a plurality of drivers each coupled to a respective capacitor opposite the common node, a first switch coupled to the common node to couple the common node to a ground in response to a second clock signal from a timing generator, a second switch coupled to the common node to couple the common node to a reference voltage in response to a third clock signal from the timing generator, a successive logic circuit configured to control each driver to alternately drive the second clock signal to a selected capacitor or to couple the selected capacitor to ground, and measurement logic including a current sensor to measure a current through the common node and configured to determine a capacitance of the selected capacitor.