Sensor Calibration Circuitry Using Macro and Micro Offset Switching
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Solution Overview
Problem
Image sensors are sensitive to manufacturing and environmental variations, leading to DC offset inconsistencies that affect downstream processing circuitry, necessitating inefficient and time-consuming calibration due to signal saturation in ADCs.
Innovation Solution
Implementing circuitry that applies a macro offset during calibration to bring the signal within the ADC's dynamic range and determines a micro offset based on the digital output, allowing for a single calibration iteration to correct signal levels, thereby maximizing dynamic range usage and minimizing clipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional calibration methods are used without macro offset, then the ADC dynamic range is fully utilized, but multiple calibration iterations are required due to signal saturation
Solution Approach 1:
The patent applies a macro offset to the input signal before ADC conversion during calibration phase. This preliminary action prevents signal saturation at the ADC input, allowing the calibration process to complete in a single iteration rather than requiring multiple iterations to gradually adjust gain and offset parameters.
2Productivity
If macro offset is applied during calibration, then calibration converges in one iteration, but additional circuitry complexity is introduced
Solution Approach 1:
The patent segments the offset correction into two distinct components: a macro offset applied during calibration phase to prevent saturation and enable single-iteration convergence, and a micro offset applied during measurement phase for fine-tuning. This segmentation allows each component to be optimized for its specific purpose without compromising the other.
Solution Approach 2:
The patent implements dynamic switching between macro offset and micro offset based on the operational phase. The macro offset is enabled during calibration phase and disabled during measurement phase, while the micro offset is disabled during calibration and enabled during measurement. This dynamic behavior allows the system to maintain simplicity during normal operation while achieving rapid calibration when needed.
3Measurement precision
If DC offset variations are not compensated, then circuitry remains simple, but downstream processing accuracy deteriorates
Solution Approach 1:
The patent introduces an intermediary offset correction mechanism that processes the sensor signal before it reaches the downstream processing circuitry. The macro offset corrects large-scale DC offset variations that would otherwise saturate the ADC, while the micro offset corrects residual offset errors. This intermediary correction ensures accurate signal processing without requiring changes to the downstream processing circuitry.
Data Source
AI summary
Circuitry for processing an input signal from a sensor, the circuitry comprising: an input configured to receive the input signal; bias circuitry configured to apply a bias to the input signal to obtain a biased input signal; a gain stage configured to apply a gain to the biased input signal to obtain an amplified input signal; an analog-to-digital converter (ADC) configured to convert the amplified input signal to a digital output signal; wherein, during a calibration phase, the control circuitry is configured to: control the bias circuitry to apply a macro offset to the input signal, the macro offset to bring the amplified input signal within a dynamic range of the ADC; and determine a micro offset to be applied during a measurement phase of the sensor based on the macro offset and the digital output signal; and wherein during the measurement phase, the control circuitry is configured to control the bias circuitry to disable application of the macro offset and apply the micro offset to the input signal, the macro offset having a greater magnitude than the micro offset.