Transimpedance Gain Circuit for Low-Mismatch Dynamic Vision Pixels
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Solution Overview
Problem
Dynamic vision sensors (DVS) face challenges in achieving high sensitivity to temporal contrast with minimal power and area consumption, as existing voltage amplification circuits using capacitors result in significant gain mismatch between pixels, leading to reduced sensitivity and increased area usage due to large capacitors, and sequential stages compromise speed.
Innovation Solution
A low-mismatch and low-consumption transimpedance gain circuit using current mirrors and transistors in series, with controlled gain, to amplify photodiode current and reduce pixel mismatch, allowing for faster and more efficient voltage amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage amplification is performed using capacitors to achieve high gain (20-100x), then the sensitivity to temporal contrast is improved, but the area consumption increases significantly due to large capacitor values required
Solution Approach 1:
The patent changes the fundamental parameter from capacitive amplification to transimpedance amplification using current mirrors. Instead of using capacitors with values proportional to gain (20-100x), the invention uses a chain of transistors in diode configuration where the gain is determined by the ratio of transistor dimensions and bias currents, achieving high gain without large area-consuming capacitors
Solution Approach 2:
The patent substitutes the capacitive voltage amplification mechanism with a transimpedance current amplification mechanism using current mirrors and transistors. This replacement eliminates the need for large capacitors while achieving the desired amplification effect, reducing area consumption significantly
2Measurement precision
If two consecutive amplification stages are used to achieve high gain through multiplication, then the voltage gain is improved, but the synchronization time increases, reducing the speed of the DVS
Solution Approach 1:
The patent segments the amplification function into a chain of individual transistor stages, each contributing to the overall gain. Instead of using two slow capacitive stages, multiple fast transistor stages are connected in series, where each transistor operates independently to provide incremental gain multiplication without requiring synchronization between stages
Solution Approach 2:
The patent employs dynamic current mirroring through transistors that can rapidly respond to input changes. The transistors in diode configuration provide fast switching and amplification capabilities, enabling high-speed operation compared to slower capacitive circuits
3Measurement precision
If voltage amplification is performed within each pixel to improve sensitivity, then the temporal contrast detection is improved, but the power consumption increases
Solution Approach 1:
The patent changes from voltage amplification to transimpedance amplification, operating directly with the photocurrent signal. This approach eliminates the need for high-voltage swings and associated power consumption, achieving amplification through current mirroring which is more energy-efficient
Solution Approach 2:
The patent uses simple transistor structures in diode configuration that consume minimal power compared to complex capacitive amplification circuits. The transistors operate in a manner that allows low bias currents while maintaining high gain, reducing overall power consumption per pixel
4Measurement precision
If large capacitors are used to achieve the required gain ratio (20-100x), then the amplification performance is improved, but the area consumption increases as capacitor area is proportional to their value
Solution Approach 1:
The patent fundamentally changes the amplification mechanism from capacitive to transistor-based transimpedance amplification. The gain is achieved through the product of individual transistor gains in a chain, where each transistor's gain is determined by its dimensional ratios and bias conditions, eliminating the need for large-area capacitors
Solution Approach 2:
The patent transitions from using capacitance values (one dimension) to using transistor dimension ratios and current ratios (another dimension) to achieve gain. This allows high gain to be achieved through geometric scaling of transistor dimensions rather than through large capacitor values
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 achieves low-mismatch voltage amplification across pixels, reducing area consumption and increasing sensitivity while maintaining fast response times, by using current mirrors and transistors in series to control gain and amplify photocurrent.
Implementation Method 1
each pixel calculates the time derivative of the light it senses... the photocurrent Iph sensed by a photo sensor is firstly transformed into voltage
Implementation Method 2
by using means for controlling polarity and gain (2) of a current generated in the at least one photodiode, preferably current mirrors
Implementation Method 3
Each one of the transistors is connected in diode configuration and is fed by an amplified copy of the photodiode current... the at least two transistors have an exponential voltage-current characteristic
Data Source
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AI summary
The invention relates to a low-mismatch and low-consumption transimpedance gain circuit for temporally differentiating photo-sensing systems in dynamic vision sensors, which uses at least one photodiode and at least two in-series transistors, each of the transistors being connected in diode configuration and being positioned at the output of the photodiode. The output current from the photodiode flows through the drain-source channels of the transistors and the source of the last transistor in series is connected to a voltage selected from ground voltage, a constant voltage or a controlled voltage.