Imaging Apparatus Load Transistor Bias Current Control
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Solution Overview
Problem
Imaging apparatuses, such as CMOS image sensors, face challenges in reading pixel signals quickly due to parasitic capacitance and switching noise, leading to unstable and slow signal voltage reading.
Innovation Solution
An imaging apparatus with a load transistor that supplies a bias current to an amplifier transistor, utilizing a voltage supply unit to input different voltage values through an input capacitor, increasing the current value during specific voltage inputs to enhance the slew rate and reduce settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a switch of a constant current circuit is operated to increase the bias current, then the reading speed of pixel signal is improved, but the settling time becomes longer due to parasitic capacitance charging
Solution Approach 1:
The patent applies preliminary action by pre-charging the parasitic capacitance before the current increase switching operation. The capacitor is charged in advance through a dedicated charging path, so when the switching occurs to increase bias current, the capacitance is already prepared and does not cause additional settling delay. This resolves the contradiction by performing the necessary charging action before it would otherwise interfere with the signal reading speed improvement.
2Speed
If the load control signal is controlled to increase the operating current, then the reading speed is improved, but switching noise is generated resulting in longer settling time
Solution Approach 1:
The patent introduces an intermediary capacitor that acts as a buffer between the control signal and the current increase operation. The capacitor smooths the switching transitions by providing a controlled charging path, thereby reducing the generation of switching noise while still achieving the current increase needed for faster reading. This intermediary element resolves the contradiction by decoupling the direct switching action that causes noise from the current increase benefit.
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 allows for stable and faster reading of pixel signal voltages, particularly when the amount of pixel signal charges is large, reducing settling time by up to 2 μs and maintaining high-speed reading across varying ISO speed values.
Implementation Method 1
a voltage supply unit configured to input one of a first voltage and a second voltage, which have different voltage values, to a control node of the load transistor via an input capacitor
Data Source
AI summary
Provided is an imaging apparatus, including: a photoelectric conversion element; an amplifier transistor configured to output a voltage corresponding to electric charges generated by the photoelectric conversion element; a load transistor configured to supply a bias current to the amplifier transistor; and a voltage supply unit configured to input one of a first voltage and a second voltage, which have different voltage values, to a control node of the load transistor via an input capacitor. In the imaging apparatus, a current value of the bias current to be supplied by the load transistor at a time when the second voltage is input to the control node via the input capacitor is larger than a current value of the bias current to be supplied by the load transistor at a time when the first voltage is input to the control node via the input capacitor.