Image Sensor Comparator Circuit for Low-Voltage ADC Linearity
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Solution Overview
Problem
Image sensors face challenges in maintaining linearity of analog-to-digital conversion when the power supply voltage is lowered, leading to potential signal level exceedance and loss of conversion linearity.
Innovation Solution
Incorporating differential pair transistors with load transistors and capacitance units in the comparator circuit, allowing for variable capacitance and amplification units to manage signal levels and reference voltages, ensuring linearity even at reduced power supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power supply voltage is lowered to achieve lower power consumption, then power consumption is reduced, but the linearity of analog-to-digital conversion deteriorates and signal levels may exceed the comparator's input dynamic range
Solution Approach 1:
The patent applies dynamics by making the capacitance value variable rather than fixed. The capacitance unit's capacitance value is changed according to the power supply voltage level, allowing the comparator to adapt its input dynamic range to match the available voltage headroom. This dynamic adjustment ensures that the pixel signal remains within the valid input range of the comparator even when power supply voltage varies, thereby maintaining conversion linearity across different power consumption modes.
Solution Approach 2:
The patent changes the capacitance parameter of the capacitance unit based on power supply voltage conditions. By adjusting the capacitance value, the input dynamic range of the comparator is modified to accommodate different voltage levels. This parameter change allows the system to maintain proper signal levels and conversion linearity while operating at reduced power supply voltages for lower power consumption.
2Use of energy by moving object
If the power supply voltage is lowered, then power consumption is reduced, but the signal level may exceed the input dynamic range of the comparator
Solution Approach 1:
The capacitance unit provides dynamic adjustment of the comparator's input dynamic range by varying its capacitance value according to the power supply voltage. When power supply voltage is reduced, the capacitance value is adjusted to expand the input dynamic range accordingly, preventing signal clipping and maintaining measurement precision across different operating conditions.
Solution Approach 2:
The patent modifies the capacitance parameter of the capacitance unit to adapt the comparator's input dynamic range to the available power supply voltage. This parameter adjustment ensures that the pixel signal remains within the valid input range of the comparator, maintaining measurement precision even when operating at reduced power supply voltages for lower power consumption.
Data Source
AI summary
An image sensor including a pixel array section in which a plurality of pixels including photoelectric conversion units is disposed, and a comparator that compares an analog pixel signal output from the pixels to a predetermined reference signal, and outputs a comparison result according to a signal level of the pixel signal. The comparator includes differential pair transistors, a first load transistor connected in series with a first transistor of the differential pair, and a second load transistor connected in series with a second transistor of the differential pair. The first transistor of the differential pair accepts a signal obtained by combining the pixel signal and the predetermined reference signal as a gate input, the second transistor of the differential pair accepts a predetermined voltage as a gate input. In addition, a capacitance unit is connected between a common connection node of the first transistor of the differential pair and the first load transistor, and a node of the predetermined voltage.