Charge Multiplying CCD Sensor Dynamic Routing Switch
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Solution Overview
Problem
Conventional Charge Coupled Device (CCD) image sensors face limitations in dynamic range due to charge multiplication, leading to blooming and reduced ability to detect low charge packets, necessitating additional output amplifiers that compromise image processing by not utilizing charge multiplying shift registers for dark regions.
Innovation Solution
An image sensor design featuring a charge directing switch that dynamically routes charge packets to either a charge multiplying shift register or a discharging element based on packet size, along with a non-destructive sense node and amplifiers, allowing for selective use of charge multiplying and charge sensing output channels to enhance dynamic range and prevent blooming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge multiplication is applied to all charge packets, then detection of low charge packets is improved, but blooming occurs in bright regions reducing dynamic range
Solution Approach 1:
The patent implements dynamic routing of charge packets based on their intensity. A charge directing switch dynamically directs low charge packets to the charge multiplying shift register for amplification while directing high charge packets to a discharging element, preventing blooming. This dynamic adaptation allows the system to optimize detection for each individual charge packet rather than applying a static multiplication approach to all packets.
Solution Approach 2:
The patent segments the charge packet processing into two distinct paths: one for low charge packets that requires multiplication and one for high charge packets that would cause blooming. The charge directing switch creates separate processing channels - one leading to the charge multiplying shift register and another leading to the discharging element - allowing different processing strategies to be applied to different segments of the input signal spectrum.
2Object-affected harmful factors
If a second output amplifier is added to read out bright regions without charge multiplication, then blooming is prevented, but dark regions do not receive charge multiplication benefit
Solution Approach 1:
The charge directing switch serves multiple functions: it routes low charge packets to the charge multiplying shift register for amplification and routes high charge packets to the discharging element to prevent blooming. This single component enables the system to handle both dark and bright regions appropriately, making the charge multiplication mechanism universally applicable to different signal conditions without requiring separate readout paths for each region type.
3Measurement precision
If charge multiplication gain is increased to detect lower charge packets, then detection threshold is reduced, but maximum measurable signal decreases reducing dynamic range
Solution Approach 1:
The patent changes the effective gain parameter dynamically based on the input signal level. For low charge packets, the charge multiplying shift register applies high gain (multiplication factor of 2 to 1000) to raise the detection threshold. For high charge packets, the charge directing switch bypasses the multiplication register and directs packets to the discharging element, effectively applying zero gain to prevent saturation. This parameter change allows the system to optimize detection threshold without compromising maximum measurable signal.
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 improves the dynamic range of CCD image sensors by selectively applying charge multiplication only when necessary, preventing blooming and enabling detection of a wider range of charge packets without compromising dark region processing, thus enhancing image capture capabilities.
Implementation Method 1
Charge multiplication occurs in charge multiplying HCCD shift register 110 through the application of large electric fields to the gate electrodes (not shown) overlying HCCD shift register 110 during charge transfer. The large electric fields produce a signal larger than originally collected in the pixels in pixel array 100.
Implementation Method 2
The multiplied charge packet output at the end of charge multiplying HCCD shift register 110 is sensed and converted into a voltage signal by output amplifier 120.
Data Source
AI summary
An image sensor includes a horizontal shift register electrically connected to a pixel array for receiving charge packets from the pixel array. A non-destructive sense node is connected to an output of the horizontal shift register. A charge directing switch is electrically connected to the non-destructive sense node. The charge directing switch includes two outputs. A charge multiplying horizontal shift register is electrically connected to one output of the charge directing switch. A discharging element is connected to the other output of the charge directing switch.