A/D Converter Voltage Stabilization via Capacitor Bypass
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Solution Overview
Problem
Existing solid state image pickup devices face challenges in reducing voltage level changes and digital value errors due to operation currents of A/D converting circuits, particularly when mounted for each column, leading to increased size and complexity.
Innovation Solution
Incorporating a switching circuit that connects a capacitor between the A/D converting circuit and the power supply, allowing the capacitor to act as a bypass during sampling, thereby stabilizing voltage levels and reducing errors in digital values without increasing the device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an A/D converting circuit is mounted for each column of pixels, then A/D conversion accuracy is improved, but voltage level changes and digital value errors increase due to operation currents
Solution Approach 1:
A capacitor is introduced as an intermediary component between the A/D converting circuit and the power supply terminal. This capacitor acts as a local energy storage device that mediates the interaction between the operating circuit and the power supply, absorbing current fluctuations and preventing direct voltage level changes that would otherwise affect conversion accuracy.
Solution Approach 2:
The capacitor is positioned beforehand between the A/D converting circuit and power supply to cushion against voltage fluctuations before they can affect the conversion process. By placing this energy buffer in advance, the system prepares for and mitigates the harmful effects of operation current variations on voltage stability.
2Reliability
If a capacitor is added to stabilize voltage levels, then voltage level changes are reduced, but device size and circuit area increase
Solution Approach 1:
The capacitor serves multiple functions simultaneously: it stabilizes voltage levels by filtering operation current fluctuations, acts as a local energy buffer for the A/D converting circuit, and reduces digital value errors. By consolidating these functions into a single component, the design avoids adding multiple separate circuits that would increase overall area.
Solution Approach 2:
The invention optimizes the capacitor's electrical parameters (capacitance value, voltage rating) to achieve the necessary voltage stabilization with the minimum possible physical size. By carefully selecting parameters that provide adequate filtering effect, the design minimizes the capacitor's footprint while maintaining effectiveness.
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 configuration effectively reduces voltage level changes and digital value errors, maintaining consistent operation currents and improving the accuracy of A/D conversion without increasing the device's size or circuit area.
Implementation Method 1
In order to reduce a change in voltage levels of an input and a GND caused by an operation of an A/D converting circuit of each column, a capacitor is connected between a power supply terminal and an input terminal of a delay circuit
Data Source
AI summary
A solid state image pickup device may include a pixel unit that includes a photoelectric conversion element, the pixel unit including a plurality of pixels that are arranged in a form of a two-dimensional matrix in the pixel unit, each of the plurality of pixels outputting a reset signal and a pixel signal, an analog signal processing unit that includes a first capacitor and a second capacitor, a delay circuit that includes a plurality of delay elements that are connected in a ring form, an A/D converter that detects the number of stages in which the pulse signal has propagated through the delay elements in the delay circuit during a sampling time period and generates a digital signal based on the detected number of stages, and a switching circuit that switches a connection of the first capacitor.