Self-Calibrating Integrating ADC for High-Resolution Microcontrollers
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Solution Overview
Problem
Contemporary microcontrollers often include complex and costly sub-ranging ADCs or fast but noise-immune SAR ADCs, which are not suitable for applications requiring a faster and more inexpensive ADC with higher resolution, such as motor control systems.
Innovation Solution
A microcontroller integrated circuit with an integrating analog-to-digital converter (IADC) featuring in-situ autocalibration capabilities, using on-chip voltage reference generators to automatically calibrate the ADC, ensuring operation within a linear range and maintaining accuracy across temperature and voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sub-ranging ADC is used, then resolution is improved, but device complexity and cost increase
Solution Approach 1:
The ADC conversion process is segmented into multiple successive integration phases, where each phase processes a portion of the conversion. The integrating ADC divides the conversion into a first integration phase using a first integrator and a second integration phase using a second integrator, allowing high resolution to be achieved through sequential processing rather than complex simultaneous circuitry.
Solution Approach 2:
An on-chip voltage reference generator circuit is introduced as an intermediary component to provide calibrated reference voltages to the ADC. This intermediary element enables automatic calibration of the ADC by generating precise reference levels, improving measurement precision without requiring external calibration equipment or complex manual adjustment circuits.
2Speed
If a SAR ADC is used, then speed is improved, but measurement precision deteriorates
Solution Approach 1:
The ADC employs periodic integration phases alternating between a first integrator and a second integrator. The conversion process uses successive approximation with periodic switching between integration stages, combining the speed of sequential processing with the precision of multiple integration phases. The calibration process also uses periodic action by sequentially applying different reference voltages to determine optimal conversion parameters.
3Measurement precision
If external calibration signals are used, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The voltage reference generator circuit provides self-service calibration by automatically generating the necessary reference voltages and calibration signals internally. The ADC calibrates itself through the on-chip reference generator without requiring external calibration equipment or manual intervention, maintaining high measurement precision while simplifying operation. The system performs self-calibration by sequentially applying reference voltages and storing the results for use during conversion.
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.