Adaptive Ramp ADC Multiple Conversion for Low-Signal Noise Reduction
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Solution Overview
Problem
Conventional image sensors face limitations in image quality due to temporal noise, and existing methods to reduce noise, such as enlarging device area or using oversampling ADCs, are either impractical or come with additional circuit costs and slower conversion speeds.
Innovation Solution
The implementation of adaptive multiple conversion ramp analog-to-digital converters (ADCs) that adjust the number of conversions based on signal level, using a modified ramp signal generator and control circuit to optimize conversions, thereby reducing noise and improving resolution without increasing conversion time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional multiple sampling is used to reduce temporal noise, then noise reduction is achieved, but conversion speed becomes slower and additional circuit cost is incurred
Solution Approach 1:
The patent implements dynamic multiple sampling where the number of samples taken by the ADC is adjusted based on the signal level. For low signal levels, more samples are taken to reduce quantization noise through averaging. For high signal levels, fewer samples are taken to maintain fast conversion speed. This dynamic adaptation resolves the contradiction between noise reduction and conversion speed.
Solution Approach 2:
The system changes the sampling parameter (number of samples) based on the input signal amplitude. When the signal level is below a threshold, the ADC performs multiple conversions and averages the results. When the signal level is above the threshold, the ADC performs single conversion. This parameter change strategy optimizes both noise reduction and conversion speed for different signal conditions.
2Measurement precision
If the number of ADC conversions is increased to reduce quantization noise, then measurement precision improves, but conversion time increases
Solution Approach 1:
The patent implements dynamic multiple sampling where the number of samples taken by the ADC is adjusted based on the signal level. For low signal levels, more samples are taken to reduce quantization noise through averaging. For high signal levels, fewer samples are taken to maintain fast conversion speed. This dynamic adaptation resolves the contradiction between noise reduction and conversion speed.
Solution Approach 2:
The system applies partial multiple sampling rather than always performing full multiple sampling. Only when the signal level is low (below threshold) does the system perform multiple conversions and averaging. For high signal levels, single conversion is sufficient. This partial application of multiple sampling reduces the time loss while still achieving noise reduction where needed.
3Measurement precision
If device area is enlarged to reduce temporal noise, then noise performance improves, but layout and size constraints are violated
Solution Approach 1:
The patent replaces the physical approach of reducing noise by enlarging device area with a computational approach using multiple sampling and averaging in the ADC. Instead of increasing the physical size of the sensor to reduce temporal noise, the system uses software-controlled multiple conversions and digital averaging to achieve noise reduction while maintaining the same physical footprint.
Solution Approach 2:
The system changes the sampling parameter (number of samples) based on the input signal amplitude. When the signal level is below a threshold, the ADC performs multiple conversions and averages the results. When the signal level is above the threshold, the ADC performs single conversion. This parameter change strategy optimizes both noise reduction and conversion speed for different signal conditions.
Data Source
AI summary
An example ramp analog-to-digital converter (ADC) for generating at least one bit of a digital signal includes a modified ramp signal generator, a comparator, and a control circuit. The modified ramp signal generator receives a ramp signal and generates a modified ramp signal in response thereto. The comparator compares an analog input with the modified ramp signal. The control circuit controls the modified ramp signal generator, such that the analog input is converted a variable M number of times for each period of the ramp signal. The number M is dependent on a magnitude of the analog input. In one example, the number M is greater for analog inputs of a lower magnitude, such that the analog inputs of the lower magnitude are converted more times than analog inputs of a higher magnitude.