Shared Amplifier A/D Conversion Circuit for CMOS Image Sensors
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Solution Overview
Problem
In solid-state imaging devices, such as CMOS image sensors, the integration of signal amplifying and A/D conversion circuits results in increased area occupation due to their independent functional nature, making it difficult to achieve both small area occupation and noise reduction simultaneously.
Innovation Solution
An A/D conversion circuit is designed with a configuration that allows for shared use of circuit elements for both signal amplification and A/D conversion by performing these operations at different times, utilizing an input capacitance, operational amplifier, and switches to manage signal and reference voltages, thereby reducing the overall circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If signal amplifying circuit and A/D conversion circuit are incorporated independently, then noise reduction is achieved, but occupation area increases
Solution Approach 1:
The patent merges the signal amplifying circuit and A/D conversion circuit into a single integrated circuit. The operational amplifier serves dual purposes: as a signal amplifier during the amplification phase and as a comparator during the A/D conversion phase. This merging eliminates the need for separate independent circuits, thereby reducing occupation area while maintaining noise reduction capabilities through the shared operational amplifier's controlled operation.
Solution Approach 2:
The operational amplifier is designed to perform multiple functions within the same circuit. It functions as a signal amplifier when the first switch is closed and as a comparator when the second switch is closed. This multi-functionality allows a single circuit element to replace what would traditionally require separate dedicated circuits, thus reducing the overall occupation area while preserving the noise reduction benefits of both functions.
2Area of stationary object
If signal amplifying circuit and A/D conversion circuit are merged, then occupation area is reduced, but functional independence is lost
Solution Approach 1:
The patent introduces dynamic switching control to manage the operational amplifier's function. Control signals dynamically switch the operational amplifier between amplification mode and comparison mode through the first and second switches. This dynamic reconfiguration allows the circuit to adapt its function based on operational requirements, maintaining functional independence and versatility despite the physical merging of circuits.
Solution Approach 2:
The circuit operates in periodic cycles, alternating between signal amplification phase and A/D conversion phase. During each cycle, the operational amplifier performs one function at a time under controlled switching. This periodic action ensures that both amplification and comparison functions are executed with proper timing and isolation, maintaining functional independence while utilizing the same physical circuit elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the occupation area of the A/D conversion circuit and enhances signal-to-noise ratio by allowing common use of circuit elements for amplification and conversion, while maintaining effective noise reduction and area efficiency.
Implementation Method 1
an input capacitance, to one end of which an input signal and a reference signal are sequentially applied; a feedback capacitance, one end of which is connected to the first input end of the operational amplifier
Implementation Method 2
a second switch that is connected between the other end of the feedback capacitance and an output end of the operational amplifier, and is turned on when an electric charge accumulated in the input capacitance is transferred to the feedback capacitance
Data Source
AI summary
An A/D conversion circuit includes: an input capacitance to which an input signal and a reference signal are sequentially applied; an operational amplifier; a first switch connected between the other end of the input capacitance and a first input end of the operational amplifier; a feedback capacitance connected to the first input end of the operational amplifier; a second switch connected between the other end of the feedback capacitance and an output end of the operational amplifier; a third switch selectively applying a predetermined voltage to the other end of the feedback capacitance; a fourth switch selectively causing a short circuit between the first input end and the output end of the operational amplifier; a fifth switch applying the predetermined voltage to a second input end of the operational amplifier; and a sixth switch applying a ramp reference voltage to the second input end of the operational amplifier.