TFET Differential Amplifier for Low-Noise Imaging
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Solution Overview
Problem
Conventional semiconductor imaging devices face challenges in reducing thermal noise from transistors, as the subthreshold coefficient of MOSFETs has a theoretical lower limit, making it difficult to suppress thermal noise below a certain noise level.
Innovation Solution
The use of Tunnel Field Effect Transistors (TFETs) for amplifying the difference between pixel and reference signals, along with a MOSFET supplying constant current, reduces thermal noise and allows for a more compact design by sharing sources and drains on a substrate, thereby reducing noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If MOSFETs are used for the differential pair in the comparator, then the device can operate with standard transistor characteristics, but thermal noise cannot be suppressed below a certain noise level due to the theoretical lower limit of the subthreshold coefficient
Solution Approach 1:
The patent changes the fundamental transistor parameter (subthreshold coefficient) by replacing MOSFETs with TFETs. TFETs inherently possess a lower subthreshold coefficient due to their tunneling-based operation mechanism, enabling thermal noise suppression below the conventional MOSFET limit without requiring additional circuit modifications or parameter adjustments within the same device type.
Solution Approach 2:
The patent substitutes the conventional MOSFET transistor mechanism with a TFET transistor mechanism. This replacement fundamentally changes the underlying physical operation from field-effect modulation to band-to-band tunneling, achieving superior noise characteristics by employing a different transistor technology platform rather than optimizing the existing MOSFET structure.
2Speed
If an ADC is arranged for each pixel to improve reading speed, then image data can be read faster, but the circuit area and complexity increase significantly
Solution Approach 1:
The patent merges the ADC functionality into a shared resource that serves multiple pixels, rather than dedicating one ADC per pixel. By implementing a column-parallel ADC architecture where each column shares an ADC, the system achieves high-speed conversion while significantly reducing the total circuit area compared to a fully pixel-parallel ADC implementation.
Solution Approach 2:
The patent segments the ADC architecture into column-level units rather than pixel-level units. This segmentation strategy divides the image sensor into multiple columns, each with its own ADC, allowing parallel processing across columns while reducing the per-pixel circuit complexity and area requirements compared to having individual ADCs for every pixel.
3Object-affected harmful factors
If constant current is increased to reduce random noise, then noise performance improves, but power consumption increases
Solution Approach 1:
The patent changes the transistor type from MOSFET to TFET, which fundamentally alters the noise characteristics. TFETs exhibit lower random noise due to their tunneling mechanism, achieving superior noise performance without requiring increased bias current. This parameter change in transistor physics allows noise reduction while maintaining or reducing power consumption levels.
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 effectively suppresses thermal noise and random noise components, reducing the need for increased constant current, which in turn lowers power consumption while maintaining image data quality.
Implementation Method 1
a pair of TFETs (Tunnel Field Effect Transistors) for amplifying the difference between the pixel signal and a predetermined reference signal
Implementation Method 2
a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) that supplies a constant current to the pair of TFETs
Implementation Method 3
a pixel circuit that generates a pixel signal by photoelectrically converting incident light
Data Source
AI summary
In a solid-state imaging element provided with a differential pair of transistors, noise of a signal from the differential pair is reduced. The semiconductor integrated circuit includes a pixel circuit and a pair of TFETs (Tunnel Field Effect Transistors). In the semiconductor integrated circuit, the pixel circuit photoelectrically converts incident light to generate a pixel signal. Further, in the semiconductor integrated circuit, the pair of TFETs amplifies the difference between the pixel signal generated by the pixel circuit and a predetermined reference signal that changes with time, and outputs the amplified difference as a differential amplification signal.