Voltage Reference Noise Filter for ADC Gain Drift
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Solution Overview
Problem
Analog-to-digital and digital-to-analog converters, particularly continuous-time sigma-delta modulators, face issues with external reference noise and gain drift due to temperature and time variations in external components, leading to performance degradation and signal-dependent errors.
Innovation Solution
A voltage reference noise filter is implemented using a resistor and capacitor configuration, with a reference gain trimming circuit that compensates for gain errors by multiplying the converter output with a scaling factor calculated during calibration, and optionally using a field programmable gate array or controller algorithm to adjust for voltage drops, ensuring minimal external components and reduced temperature-related drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage reference circuit is used in ADCs/DACs, then the converters can perform analog-to-digital or digital-to-analog conversion, but external reference noise and temperature drift adversely impact performance
Solution Approach 1:
A buffer circuit is introduced as an intermediary between the voltage reference circuit and the converter. This buffer isolates the converter from reference noise and temperature drift effects, allowing accurate conversion while protecting against external harmful factors. The buffer acts as a mediator that decouples the reference circuit from the converter's sensitive input.
Solution Approach 2:
A feedback mechanism is implemented where the converter output is fed back through a trimming circuit that adjusts the reference voltage or gain to compensate for drift and noise effects. This closed-loop feedback continuously corrects performance degradation caused by temperature variations and reference instability, maintaining measurement precision.
2Measurement precision
If techniques such as quad-switching are used to address input-dependent reference errors, then reference accuracy improves, but the circuit becomes more complex
Solution Approach 1:
The complex quad-switching network is extracted and replaced with a simpler buffer circuit configuration. The essential function of reducing reference errors is retained through the buffer's high input impedance and low output impedance characteristics, while eliminating the complexity of multiple switching elements and their control logic.
Solution Approach 2:
The circuit topology is changed from a switching-based approach to a passive buffer approach with carefully selected resistance and capacitance values. By optimizing the buffer's parameters (input impedance, output impedance, time constant), the same reference error correction function is achieved with significantly reduced circuit complexity.
3Reliability
If external components are used for voltage reference, then the reference voltage can be provided, but component values drift with temperature and time
Solution Approach 1:
The buffer circuit serves as a thermal intermediary between the external voltage reference and the converter. It isolates the converter from temperature-induced reference drift while maintaining signal integrity. The buffer's stable characteristics compensate for external component drift, improving overall reliability.
Solution Approach 2:
The buffer circuit is designed with pre-calculated resistance and capacitance values that anticipate and compensate for temperature drift effects. During calibration, the buffer parameters are optimized to counteract expected temperature variations, proactively maintaining reference stability before drift occurs.
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 effectively filters external reference noise and compensates for gain errors, maintaining signal fidelity and reducing temperature-related drift, thereby enhancing the performance and stability of the converters.
Implementation Method 1
A resistor is connected at a first end to the voltage reference circuit and at a second end to the reference terminal of the converter. Also, the circuit may further include a reference capacitor terminal connected to the second end of the resistor. The reference capacitor terminal connects the second end of the resistor to a capacitor to form a filter that filters an output of the voltage reference circuit.
Data Source
AI summary
A voltage reference noise filter is provided that substantially eliminates noise with minimal external components for any circuit where the reference load current is a constant load and the circuit uses external components that have values that may vary with temperature, over time, and the like. The drift on an output of a voltage reference due to variation of resistor of the external filter is mitigated by moving the external resistor onto the chip containing the circuit. The voltage drop across the resistor is digitally compensated by a scaling factor determined during calibration. When more than one converter is provided on the chip, a further adjustment to the outputs of the converters is made based on the number of converters powered on or off. Also, error in output of converters due to mismatch among the converters is digitally compensated by a further scaling factor.