Buffer Circuit for Solid-State Imaging Noise Reduction
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Solution Overview
Problem
Solid-state imaging devices using threshold voltage modulation image sensors face challenges in suppressing horizontal stripe noise due to noise mixed in the gate line, which affects image quality even with low input noise levels.
Innovation Solution
A detecting device and solid-state imaging device are designed with a buffer circuit that matches the transfer characteristic of the detecting circuit, generating a differential signal between the output voltage from the detecting circuit and the buffer circuit to reduce noise components and output variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a buffer circuit is added to match the transfer characteristic of the detecting circuit, then noise and output variations are reduced, but device complexity increases
Solution Approach 1:
The patent creates a buffer circuit that copies the transfer characteristic of the detecting circuit (pixel circuit). The buffer circuit uses a MOS transistor with the same characteristics as the pixel circuit's transistor, and connects its other end to the same reference voltage line, thereby replicating the noise characteristics and transfer function. This copying approach allows the differential circuit to cancel out common-mode noise while preserving the actual signal.
Solution Approach 2:
The buffer circuit acts as an intermediary between the reference voltage line and the differential circuit. Instead of directly connecting the reference voltage to the differential subtraction node, the buffer circuit mediates by providing a replicated version of the reference voltage with matched transfer characteristics, enabling effective noise cancellation without requiring direct access to the pixel circuit's internal nodes.
2Reliability
If the other end of the capacitive element is connected to the reference voltage line, then noise mixed in the gate line affects all pixels in the horizontal direction, but connecting to ground would eliminate this noise
Solution Approach 1:
The patent converts the harmful noise mixed in the reference voltage line into a beneficial signal for cancellation. By connecting the buffer circuit's other end to the same reference voltage line, the buffer replicates the exact noise characteristics. This replicated noise is then subtracted from the pixel signal in the differential circuit, transforming the originally harmful noise into a cancelable common-mode component that improves signal accuracy.
Solution Approach 2:
Instead of directly connecting the capacitive element to ground (which would eliminate noise but also eliminate the reference voltage coupling), the patent inverts the approach by connecting it to the reference voltage line and using a buffer circuit to create a differential subtraction. This inversion allows the system to maintain reference voltage coupling while actively canceling the noise through the differential operation.
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 and output variations, improving image quality by eliminating or minimizing horizontal stripe noise and enhancing the accuracy of detected signals.
Implementation Method 1
receiving irradiation light from outside as the physical input with the photodiode to perform photoelectric conversion
Implementation Method 2
the MOS transistor part of this area has a high-density buried layer for accumulating light-generated charge generated by light irradiation in the photodiode provided in the well region adjacent to the source region and under the gate electrode
Data Source
AI summary
A solid-state imaging device includes a light receiving section having a plurality of threshold voltage modulation pixel circuits each configured including a MOS transistor having a gate electrode connected to a supply terminal of a gate voltage of a vertical scanning circuit, and a source electrode connected to one end of each capacitor of a line memory group via a switching element, and a photodiode having an anode connected to a back-gate electrode of the MOS transistor and a cathode connected to a drain electrode thereof, and a buffer circuit having an input terminal connected to a supply line of a control voltage of the control voltage supply means adapted to supply the vertical scanning circuit with the control voltage, and an output terminal connected to the other end of each capacitor, and having a signal transfer characteristic the same as that of the pixel circuit.