Dynamic ADC Voltage Reference With Temperature Trim Calibration
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Solution Overview
Problem
Delta-sigma analog-to-digital converters (ADCs) face challenges in maintaining stable reference voltage across varying temperatures due to capacitor mismatch and temperature drift, leading to inaccuracies in voltage reference circuits.
Innovation Solution
A dynamic voltage reference circuit with dynamically trimmable capacitors and operational amplifiers that sample diode voltages to provide a stable reference voltage, using a method of calibration that adjusts trim control bits to match output codes and apply digital gain calibration for temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a voltage reference circuit is designed to maintain stable voltage output, then reference voltage stability is improved, but temperature drift and capacitor mismatch cause measurement precision to deteriorate
Solution Approach 1:
The patent implements a calibration circuit that measures the actual output voltage of the reference circuit and compares it against expected values. Based on this feedback, the circuit adjusts capacitor trim elements to correct for temperature drift and capacitor mismatch, thereby maintaining measurement precision while preserving voltage stability.
Solution Approach 2:
The patent employs trimmable capacitors whose capacitance values can be adjusted through calibration. By changing the capacitance parameters of these capacitors based on measured temperature and voltage conditions, the system compensates for temperature drift and capacitor mismatch effects, resolving the contradiction between stability and precision.
2Measurement precision
If multi-temperature calibration is implemented to improve precision across temperature ranges, then measurement precision is improved, but device complexity and calibration time increase
Solution Approach 1:
The patent performs capacitor trimming and calibration settings during the manufacturing process rather than requiring field calibration. This preliminary action establishes optimal capacitor values that compensate for temperature effects, achieving high precision across temperature ranges without adding complex calibration hardware or procedures for end users.
Solution Approach 2:
The calibration circuit automatically measures and adjusts capacitor trim values without requiring external calibration equipment or manual intervention. The system self-calibrates by comparing its own output against reference values and adjusting internal capacitor elements, thereby achieving temperature-compensated precision while minimizing added complexity.
3Measurement precision
If capacitor mismatch is reduced to improve precision, then measurement precision is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent introduces trimmable capacitor elements that act as intermediaries between the fixed mismatched capacitors and the reference voltage generation. These trimmable elements compensate for the mismatch by allowing post-fabrication adjustment of capacitance ratios, achieving high precision without requiring extremely tight manufacturing tolerances on all capacitors.
Solution Approach 2:
The patent makes the capacitor network dynamically adjustable through trim elements that can be programmed or adjusted after fabrication. This dynamic capability allows the system to compensate for capacitor mismatch variations, achieving high precision while maintaining ease of manufacture since the capacitors themselves don't require ultra-precise matching during fabrication.
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 achieves significant stability of the reference voltage across a range of temperatures, ensuring accurate output even when trimmed at a single temperature point, reducing the need for complex multi-temperature calibration and minimizing temperature drift.
Implementation Method 1
The voltage reference includes an input capacitor configured to sample an input voltage. The voltage reference includes a base-emitter capacitor configured to sample the first diode voltage with respect to a ground.
Implementation Method 2
dynamic diode elements configured to provide first and second diode voltages
Implementation Method 3
The voltage reference includes a dynamically trimmable capacitor configured to sample the first diode voltage with respect to the second diode voltage. The op amp is configured to provide a reference voltage based on the sampled input voltage, the first and second diode voltages, and a trim of the trimmable capacitor.
Data Source
AI summary
A calibratable switched-capacitor voltage reference and an associated calibration method are described. The voltage reference includes dynamic diode elements providing diode voltages, input capacitor(s) for sampling input voltages, base-emitter capacitor(s) for sampling one diode voltage with respect to a ground, dynamically trimmable capacitor(s) for sampling the one diode voltage with respect to another diode voltage, and an operational amplifier coupled to the capacitors for providing reference voltage(s) based on the sampled input and diode voltages and on trims of the trimmable capacitor(s). The voltage reference can be configured as a first integrator of a modulator stage of a delta-sigma analog-to-digital converter.