Capacitance Measurement Circuit Using Direct ADC Conversion
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Solution Overview
Problem
Conventional capacitive measurement systems are too slow for fast conversion applications and lack a digital response, making them unsuitable for applications requiring rapid data processing.
Innovation Solution
A capacitance measurement system that includes a variable capacitor and at least one reference capacitor connected to a common node, which is directly connected to an analog-to-digital (A-to-D) converter, along with an array of switches to perform multiple voltage measurements, generating an expression for capacitance that is independent of error sources such as sample-and-hold capacitance and parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional capacitive measurement system with charge comparator and integrator buffer is used, then the system can perform capacitance measurements, but the response time is too slow for fast conversion applications
Solution Approach 1:
The patent extracts and removes the complex integrator buffer and charge comparator stages from the measurement system. Instead, it directly connects the capacitor under test to an analog-to-digital converter, eliminating the slow analog processing stages while maintaining measurement capability through direct digital conversion of the capacitor's charge state.
Solution Approach 2:
The patent replaces the mechanical/analog signal processing chain (charge comparator, integrator buffer, voltage-to-current stage) with a direct digital conversion approach. The analog capacitor charge is directly converted to digital values by the ADC, substituting complex analog circuitry with a simpler digital measurement process that achieves faster response time.
2Productivity
If a conventional capacitive measurement system is used, then the system can measure capacitance, but it lacks fast digital response for rapid data processing applications
Solution Approach 1:
The patent substitutes the conventional analog measurement chain with a direct digital conversion system. The capacitor is connected directly to an ADC, which provides immediate digital output values. This substitution enables fast digital response for rapid data processing while the multiple measurement technique ensures measurement precision by eliminating analog error accumulation.
Solution Approach 2:
The patent performs multiple voltage measurements (at least two measurements) to determine the capacitance value. This excessive measurement approach provides redundant data that can be processed to eliminate error sources such as sample-and-hold capacitance and parasitic capacitance, thereby maintaining high measurement precision while enabling fast digital output.
3Measurement precision
If multiple voltage measurements are performed to eliminate error sources, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs multiple voltage measurements in a continuous sequence without interrupting the measurement process. The capacitor remains connected to the ADC throughout, and multiple readings are taken rapidly to generate multiple voltage values. This continuous measurement approach eliminates idle time between measurements, reducing total measurement time while maintaining precision through error elimination.
Solution Approach 2:
The patent uses periodic switching of the capacitor connections to the ADC to perform multiple measurements. By periodically switching between different measurement configurations (connecting the capacitor to different reference voltages or ground), the system rapidly collects multiple voltage values that can be processed to eliminate systematic errors, achieving both precision and speed.
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 system achieves a fast digital response and reduced output error by using the A-to-D converter to perform voltage measurements that eliminate common error sources, enhancing the accuracy and speed of capacitance measurements.
Implementation Method 1
an analog-to-digital (A-to-D) converter... perform, at the common node, a plurality of voltage measurements which are subsequently used to generate an expression defining the capacitance
Data Source
AI summary
An improved system and method of performing capacitance measurements that provides a fast digital response and a reduced output error. The capacitance measurement system includes a circuit configuration that has a variable capacitor and at least one reference capacitor connected to one another at a common node, which in turn is connected to the input of an analog-to-digital converter. The circuit configuration further includes an array of switches coupled between the variable and reference capacitors and the supply voltage, a reference voltage, and ground, respectively. The switched variable and reference capacitors are employed in conjunction with the A-to-D converter to perform, at the common node, a plurality of direct voltage measurements for use in generating an expression defining the capacitance of the variable capacitor.