Voltage-Shifting Readout Circuit for Low-Voltage ADC Precision
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Solution Overview
Problem
Conventional image sensor readout circuits require high voltage to match the pixel output swing, leading to increased power consumption and cost, while signal attenuation methods result in information loss and bit errors during digital conversion.
Innovation Solution
A readout circuit comprising a comparator and level-shifting circuit that reduces the voltage swing of the pixel signal without attenuating it, using a storage device and switching devices to sample and shift the signal, allowing the ADC to operate within a lower voltage range while maintaining signal precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ADC operates at high voltage to match the pixel output swing, then the signal can be converted without attenuation, but the power consumption increases
Solution Approach 1:
The readout circuit is divided into multiple functional stages: a sample and hold circuit that operates at high voltage to capture the pixel signal, a level-shifting circuit that transitions the voltage to a lower range, and an ADC that operates at the reduced voltage. This segmentation allows each component to operate at its optimal voltage level, maintaining signal accuracy while reducing overall power consumption.
Solution Approach 2:
A level-shifting circuit acts as an intermediary between the high-voltage pixel output and the low-voltage ADC. This intermediate stage translates the voltage level without attenuating the signal, enabling the ADC to process the signal at lower power while preserving measurement precision.
2Use of energy by moving object
If the signal is attenuated to reduce voltage, then the ADC can operate at lower voltage, but information is lost and bit errors are introduced
Solution Approach 1:
The sample and hold circuit performs preliminary action by capturing and storing the high-voltage pixel signal before it is passed to the level-shifting circuit. This preliminary sampling ensures that the full signal information is preserved in the held voltage, which is then translated to a lower voltage range without loss of information.
Solution Approach 2:
The level-shifting circuit serves as an intermediary that performs voltage translation rather than attenuation. By using controlled voltage level shifting, the circuit maintains the signal's information content while adapting it to the lower operating voltage required by the ADC, thereby avoiding bit errors.
3Measurement precision
If amplifiers are used to increase the pixel output swing, then the signal can match the ADC input swing, but the cost and power consumption increase
Solution Approach 1:
Instead of using amplifiers to increase the signal swing to match the ADC input, the invention inverts the approach by reducing the voltage level after sampling. The sample and hold circuit captures the full pixel output swing, and then the level-shifting circuit translates it to a lower voltage range, eliminating the need for high-voltage ADC operation and complex amplification stages.
Data Source
AI summary
Methods and device for a readout circuit according to various aspects of the present invention may operate in conjunction with a storage device selectively coupled to an input signal having a voltage value within a first voltage range. A comparator may compare the voltage value of the input signal to a predetermined threshold voltage. A level-shifting circuit may shift the first voltage value of the input signal to a second voltage value within a second voltage range if the first voltage value of the input signal is greater than the predetermined threshold voltage.