Direct Capacitance-to-Digital Conversion Without External Amplifiers
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Solution Overview
Problem
Conventional analog-to-digital converters (ADC) require external amplifiers and bias circuits, leading to increased chip size, noise, and instability due to stray capacitance, which complicates integration and reduces accuracy.
Innovation Solution
A direct capacitance-to-digital converter using a trigger unit to control switches and a reference voltage circuit to directly measure capacitance changes, eliminating the need for external amplifiers and bias circuits, and incorporating a differential ADC for improved noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external amplifier and bias circuit are used to improve sensing sensitivity, then measurement precision is improved, but device complexity increases and chip area increases
Solution Approach 1:
The patent extracts and eliminates the external amplifier and bias circuit from the conventional sensing system. By using the ADC's internal comparator directly to sense the capacitance change without requiring external amplification stages, the design removes complex external components while maintaining measurement capability through direct digital conversion of the capacitance signal.
Solution Approach 2:
The ADC module serves multiple functions: it acts as both the conversion device and the sensing element. The comparator within the ADC directly compares the capacitance signal against reference levels, eliminating the need for separate amplifier and bias circuitry, thus achieving multi-functionality with a single integrated component.
2Measurement precision
If external amplifier is used to amplify low inductive voltage, then measurement precision is improved, but area of moving object increases
Solution Approach 1:
The patent merges the amplification function and voltage comparison function into the single comparator module within the ADC. By combining these functions, the design eliminates the need for separate external amplifier circuits, thereby reducing chip area while maintaining the capability to handle low inductive voltage signals through direct digital conversion.
3Measurement precision
If conventional Σ-Δ ADC structure with multiple serial stages is used to improve resolution, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the complex multi-stage serial converter structure from the conventional Σ-Δ ADC design. By using a single comparator stage with direct capacitance-to-digital conversion, the design achieves resolution improvement without requiring multiple serial conversion stages, thereby simplifying the overall converter structure.
4Measurement precision
If bias circuit is used to provide bias voltage, then measurement precision is improved, but reliability decreases due to noise
Solution Approach 1:
The patent extracts and eliminates the separate bias circuit from the design. By using the ADC's internal reference voltage and comparator directly, the design removes the noise-prone bias circuit while maintaining stable operation through the ADC's inherent reference voltage system, thereby improving reliability and noise immunity.
Data Source
AI summary
A direct capacitance-to-digital converter is provided, including a plurality of switches, an ADC, a reference voltage circuit and a trigger unit. By using trigger unit to control a plurality of switches, and combining the reference voltages outputted by the reference voltage circuit, the converter can directly sense the external to-be-measured capacitor and related stray capacitor, and directly convert the capacitance of the to-be-measured capacitor into accurate digital signal. The present invention can be integrated with other sensors into a single chip to form an integrated direct capacitance-to-digital converter.