Delta-Sigma ADC Capacitor Switching for Common-Mode Linearity
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Solution Overview
Problem
Delta-sigma A/D converters face limitations in handling differential signals with varying common mode potentials and restricted reference voltage ranges, leading to operational issues and design constraints.
Innovation Solution
The proposed solution involves a delta-sigma A/D converter configuration with a modulator and decimation filter, utilizing capacitors to sample and integrate differential signals, allowing for any common mode potential and reference voltage, through a circuit design that adjusts switch connections to maintain a common mode potential and enable flexible reference voltage settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional delta-sigma A/D converter uses fixed common mode potential handling, then the circuit operation is simplified, but it cannot handle differential signals with varying common mode potentials
Solution Approach 1:
The patent implements dynamic switching of capacitor connections to adapt to varying common mode potentials. The switch circuit dynamically reconfigures the capacitor network based on the common mode potential level, allowing the A/D converter to handle differential signals with any common mode potential while maintaining accurate conversion performance.
Solution Approach 2:
The patent changes the connection parameters of the capacitor circuit based on the common mode potential. By switching between different capacitor configurations (e.g., connecting capacitors in series or parallel, or connecting to different nodes), the circuit adapts its electrical parameters to match the input signal characteristics, enabling universal handling of different common mode potentials.
2Adaptability or versatility
If the reference voltage range is restricted, then the circuit design is simpler, but the flexibility in reference voltage settings is limited
Solution Approach 1:
The patent uses dynamic switching circuits to reconfigure capacitor connections based on the selected reference voltage. This allows the same hardware circuit to support multiple reference voltage ranges by changing its operational configuration, providing flexibility without requiring multiple dedicated circuits for each voltage range.
Solution Approach 2:
The capacitor switching circuit serves multiple functions: it enables the A/D converter to operate with different reference voltage ranges (e.g., ±2.5V, ±1.25V, ±0.625V) using the same physical components. This multi-functional design eliminates the need for separate circuits for each voltage range, reducing overall system complexity while enhancing versatility.
3Manufacturing precision
If switch connections are not adjusted for common mode potential, then the control logic is simpler, but linearity degradation occurs
Solution Approach 1:
The patent implements feedback control where the common mode potential detection circuit monitors the input signal's common mode level and provides this information to the switch control logic. This feedback mechanism automatically adjusts the capacitor connections to maintain optimal linearity across different common mode potentials without requiring complex manual calibration or control logic.
Solution Approach 2:
The A/D converter circuit performs self-adjustment by automatically detecting the common mode potential and reconfiguring its internal capacitor network accordingly. This self-service capability maintains high conversion linearity across varying input conditions without external intervention or complex control algorithms, simplifying the overall control logic.
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
This configuration allows for precise A/D conversion of differential signals with any common mode potential and flexible reference voltage settings, improving linearity and reducing nonlinearity issues, enabling high-precision A/D conversion.
Implementation Method 1
a first capacitor and a second capacitor each of which samples an input signal, a third capacitor and a fourth capacitor which are connected to the first electrode of the first capacitor and which sample a first reference voltage or a second reference voltage
Implementation Method 2
at least one arithmetic operation circuit including an arithmetic operator which performs addition or subtraction of the charges sampled by the respective capacitors to obtain an addition or subtraction result, and which integrates the addition or subtraction result
Data Source
AI summary
An arithmetic operation circuit provided in a delta-sigma modulator of a delta-sigma A/D converter includes two reference capacitors which are respectively provided at a positive side input node and a negative side input node of an operational amplifier. When a signal corresponding to an output of the modulator is added or subtracted to or from an input signal, the amount of charge added to the input node of the operational amplifier is made to be always the same regardless of the reference voltage by complementarily switching the connection of the reference capacitors at the positive side input node and the negative side input node, and thereby the potential of the input node of the operational amplifier is made to converge to the common mode potential of the circuit.