Self-Calibrating Integrating ADC for Fast High-Resolution Conversion
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Solution Overview
Problem
Contemporary microcontrollers often feature ADCs that are either complex and costly (sub-ranging) or fast but noise-immune and low-resolution (SAR), while sigma-delta ADCs provide higher resolution but are slow, lacking a balance of speed and cost-effectiveness for applications like motor control.
Innovation Solution
A microcontroller integrated circuit with an integrating analog-to-digital converter (IADC) featuring in-situ autocalibration using on-chip voltage reference generators to calibrate and control the ADC, ensuring operation within a linear range, thereby achieving faster and more cost-effective conversions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sub-ranging ADC is used, then higher resolution is achieved, but device complexity and cost increase substantially
Solution Approach 1:
The ADC conversion process is segmented into multiple phases: an initial coarse conversion phase that establishes a basic digital value, followed by a fine conversion phase that refines the result to achieve higher resolution. This segmentation allows the system to achieve sub-ranging ADC performance through a simplified architecture that combines a basic ADC with calibration and refinement logic, rather than implementing a complex sub-ranging converter directly.
Solution Approach 2:
The system performs preliminary calibration actions before the main conversion process. Calibration values are pre-determined by applying known test inputs and storing the corresponding digital outputs. During actual conversion, these pre-stored calibration values are used to correct and refine the raw ADC output, eliminating the need for complex real-time correction circuitry.
2Speed
If a SAR ADC is used, then conversion speed is improved, but measurement precision deteriorates to seven-bit to eight-bit range
Solution Approach 1:
The system maintains continuous useful action by performing calibration measurements during periods when the ADC is not actively converting production data. The calibration process is integrated into the ADC's operational cycle, utilizing idle time to update calibration values without interrupting normal conversion operations. This allows the fast SAR ADC to maintain its speed advantage while continuously improving its precision through background calibration.
3Measurement precision
If a sigma-delta ADC is used, then measurement precision is improved, but conversion speed deteriorates
Solution Approach 1:
The patent replaces the mechanical/time-intensive averaging process characteristic of sigma-delta ADCs with a computational approach. Instead of relying on long integration periods and digital filtering to achieve precision, the system uses a fast SAR ADC combined with calibration-based correction algorithms. This substitution maintains measurement precision while dramatically improving conversion speed by eliminating the need for lengthy sigma-delta modulation and decimation processes.
4Adaptability or versatility
If an integrating ADC with non-linear operating ranges is used, then wider input voltage range is achieved, but measurement precision deteriorates in non-linear ranges
Solution Approach 1:
The system dynamically changes the operating parameters of the integrating ADC by adjusting the integrator's gain or integration time based on the input signal level. For small input signals, the integrator operates in its linear region with higher gain to maximize precision. For larger input signals, the integration parameters are adjusted to prevent saturation and maintain accuracy across the extended input voltage range, effectively linearizing the ADC's response through parameter adaptation.
Data Source
AI summary
A microcontroller has an integrating analog-to-digital converter (IADC) with an in-situ autocalibrating functionality. On-chip autocalibrating circuitry supplies a first predetermined analog input voltage to the IADC and obtains a first data value from the IADC. The autocalibrating circuitry supplies a second predetermined analog input voltage to the IADC and obtains a second data value. The first and second data values are used to calibrate the IADC such that if the first input voltage is later supplied to the IADC, then the IADC will output a first predetermined desired digital output value and such that if the second input voltage is later supplied to the IADC, then the IADC will output a second predetermined desired digital output value. The first and second analog input voltages are generated on-chip so the calibration is performed automatically without having to supply external calibrating signals to the microcontroller. Other related methods and circuitry is disclosed.