ADC Capacitor Switching to Limit Noise Propagation
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Solution Overview
Problem
Conventional analog to digital converters (ADCs) in solid-state imaging elements face reliability issues due to noise propagation and capacitor failure, particularly when multiple ADCs are operated, leading to reduced performance over time.
Innovation Solution
An ADC design incorporating a differential amplifier circuit, a time measuring unit, and a switch that connects and disconnects a capacitor during conversion periods to minimize noise and capacitor stress, improving reliability by isolating the capacitor during non-conversion periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitor is connected in parallel with the amplifier circuit to increase input capacitance and reduce noise, then noise reduction is improved, but the reliability deteriorates due to capacitor failure and noise propagation during non-conversion periods
Solution Approach 1:
The capacitor connection is made dynamic through a switch that connects the capacitor to the amplifier circuit during conversion periods and disconnects it during non-conversion periods. This dynamic configuration allows the system to optimize for noise reduction when needed while avoiding reliability issues when the capacitor is not required, resolving the contradiction between noise reduction and reliability
Solution Approach 2:
The capacitor is periodically connected and disconnected based on the conversion period timing. During conversion periods, the capacitor is connected to provide noise reduction; during non-conversion periods, it is disconnected to prevent noise propagation and capacitor failure. This periodic action pattern allows the system to achieve noise reduction benefits while maintaining reliability
2Object-affected harmful factors
If the capacitor remains connected during non-conversion periods, then noise reduction is maintained, but noise propagates to other ADCs via power supply or ground systems
Solution Approach 1:
The capacitor is extracted from the amplifier circuit during non-conversion periods using a switch. By removing the capacitor from the circuit when it is not needed for noise reduction during conversion, the system prevents noise propagation through the power supply or ground systems to other ADCs, while maintaining noise reduction capability when the capacitor is reconnected during conversion periods
3Productivity
If the ADC operates for longer periods, then more conversions are performed, but the capacitor charge/discharge time increases and failure probability rises
Solution Approach 1:
The capacitor is periodically disconnected during non-conversion periods to allow it to maintain its charge state without continuous charge/discharge cycling. This periodic disconnection reduces the cumulative charge/discharge time and lowers failure probability, while still enabling high conversion throughput during active conversion periods when the capacitor is connected
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
The solution effectively reduces noise propagation and extends capacitor lifespan, enhancing the overall reliability of the ADC and solid-state imaging element.
Implementation Method 1
a capacitor having one end connected to one of an input terminal or a predetermined connection terminal of the amplifying element
Implementation Method 2
a switch configured to connect the other end of the capacitor to the other of the input terminal or the predetermined connection terminal in the conversion period and disconnect the other end from the other in a period other than the conversion period
Implementation Method 3
a differential amplifier circuit configured to amplify a difference between an input analog signal and a ramp signal which changes over time to output as a difference signal
Data Source
AI summary
A differential amplifier circuit amplifies a difference between an input analog signal and a ramp signal which changes over time and outputs a difference signal. An amplifying element amplifies the difference signal and outputs the same as an amplified signal. A time measuring unit measures a length of a conversion period until a level of the analog signal substantially coincides with a level of the ramp signal on the basis of a level of the amplified signal and outputs the same as a digital signal obtained by converting the analog signal. One end of a capacitor is connected to one of an input terminal and a predetermined connection terminal of the amplifying element. A switch connects the other end of the capacitor to the other of the input terminal or the predetermined connection terminal in the conversion period, and disconnects the other end outside the conversion period.