Switched-Capacitor ΔΣ ADC Feedback for VCO Nonlinearity
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Solution Overview
Problem
ΔΣ-type A/D converters utilizing a voltage-controlled oscillator (VCO) suffer from nonlinear frequency characteristics, leading to resolution degradation, and existing calibration techniques increase power consumption and circuit area, limiting their operational speed.
Innovation Solution
Incorporating a switched capacitor on the negative-feedback path of the ΔΣ-type A/D converter, which varies the charge amount based on the oscillation signal frequency, capacitance, and bias voltage, to generate a high-speed, high-accuracy feedback signal, replacing the need for a D/A converter and reducing circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sweeping calibration is used to correct frequency nonlinearity, then resolution is improved, but power consumption increases and operational speed decreases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for frequency nonlinearity in a lookup table during the design phase. During operation, the system simply retrieves pre-computed correction data based on the VCO frequency, avoiding real-time calibration computations and enabling high-speed operation with maintained resolution accuracy.
Solution Approach 2:
The patent replaces the mechanical/voltage-based calibration process with a digital lookup table system. Instead of performing analog voltage sweeping and real-time nonlinearity correction, the system uses a digitally stored correction table that maps frequency points to correction values, substituting complex analog calibration with simple digital retrieval operations.
2Measurement precision
If D/A converter is added to mitigate nonlinearity in VCO negative-feedback loop, then frequency linearity is improved, but circuit area increases
Solution Approach 1:
The patent extracts the nonlinearity correction function from the main signal path and implements it separately through a lookup table. By separating the correction mechanism from the VCO feedback loop, the system avoids adding complex correction circuitry while maintaining frequency linearity through simple table-based compensation.
Solution Approach 2:
The patent uses a simple lookup table structure that requires minimal hardware resources compared to a full D/A converter. The lookup table can be implemented with basic memory elements and combinatorial logic, providing an economical solution that consumes less area and power while achieving the same nonlinearity mitigation goal.
3Measurement precision
If D/A converter is used for feedback signal generation, then feedback accuracy is improved, but power consumption and circuit area increase
Solution Approach 1:
The patent replaces the power-consuming D/A converter with a lightweight lookup table implementation. The lookup table uses minimal hardware resources (basic memory and logic elements) to generate accurate feedback signals, dramatically reducing power consumption while maintaining the necessary feedback accuracy for high-resolution conversion.
Solution Approach 2:
The patent substitutes the analog D/A conversion process with a digital lookup table retrieval process. This substitution eliminates the need for analog current sources, switching networks, and associated calibration circuitry, resulting in lower power consumption and reduced circuit complexity while preserving feedback signal 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 enables high-resolution digital signal generation with improved speed and accuracy while minimizing power consumption and circuit size, effectively addressing the nonlinear frequency change issue and enhancing the converter's performance.
Implementation Method 1
a switched capacitor (8) comprising a capacitor (8c) to perform charging and discharging by switching a switch (8a, 8b), the switched capacitor (8) varying a charge amount of the capacitor (8c) in accordance with a frequency of an oscillation signal in accordance with a differential signal between an input signal and a feedback signal, capacitance of the capacitor (8c), and a predetermined bias voltage
Data Source
AI summary
An analog-to-digital converter has a switched capacitor comprising a capacitor to perform charging and discharging by switching a switch, the switched capacitor varying a charge amount of the capacitor in accordance with a frequency of an oscillation signal in accordance with a differential signal between an input signal and a feedback signal, capacitance of the capacitor, and a predetermined bias voltage, a feedback signal generator to generate the feedback signal based on an output signal of the switched capacitor, and a digital converter to generate a digital signal by digital conversion of the input signal based on the oscillation signal.