Gate Driver Circuit for Low Latency Fingerprint Sensing
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Solution Overview
Problem
Fingerprint sensors face challenges in rapidly acquiring fingerprint data after waking up from a dormant state, as the sensing pixels often operate in photovoltaic mode, leading to saturation and delayed transition to photoconductive mode, which hampers quick readout and accurate fingerprint detection.
Innovation Solution
A gate driver circuit with cascaded units is employed to generate a global reset gate control signal, driving the sensing pixels from photovoltaic to photoconductive mode, allowing for immediate readout of non-saturated frames by outputting a global reset signal during the reset phase and sequential operating gate control signals during the operating phase, facilitating rapid fingerprint acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If sensing pixels operate in photovoltaic mode during wake-up, then power consumption is reduced, but pixel saturation occurs and response time increases
Solution Approach 1:
The gate driver circuit performs a preliminary reset action by outputting a reset gate control signal to all sensing pixels before the operating phase begins. This preliminary reset clears any saturation that may have occurred during the photovoltaic mode wake-up period, preparing the pixels for immediate accurate fingerprint detection without requiring extended warm-up time.
Solution Approach 2:
The system dynamically switches between photovoltaic mode (for power saving during dormancy) and photoconductive mode (for rapid response during operation). The gate driver circuit enables this dynamic transition by controlling the operating mode of sensing pixels through gate control signals, allowing optimal performance characteristics at different operational states.
2Device complexity
If sensing pixels are reset sequentially, then circuit complexity is reduced, but readout speed decreases
Solution Approach 1:
The gate driver circuit is segmented into multiple cascaded gate driver units, each responsible for controlling a specific subset of sensing pixels. This segmentation allows parallel reset operation across different pixel subsets, achieving fast readout speed while keeping each individual gate driver unit relatively simple in structure.
Solution Approach 2:
Multiple gate driver units are merged into a cascaded configuration where the output of one unit feeds into the next. This merging enables coordinated control of all sensing pixels through a unified reset gate control signal generated from a single clock signal, maintaining circuit simplicity while achieving parallel operation speed.
3Measurement precision
If photodiodes transition from photovoltaic to photoconductive mode, then fingerprint detection accuracy improves, but transition time increases
Solution Approach 1:
The reset gate control signal performs a preliminary action by forcing all photodiodes into the photoconductive mode before the fingerprint detection process begins. This preliminary mode transition ensures that the photodiodes are already in the accurate detection state when needed, eliminating the need for slow natural transition during actual fingerprint acquisition.
Solution Approach 2:
The gate driver circuit uses periodic clock signals to control the periodic switching between photovoltaic and photoconductive modes. During each operating cycle, the reset phase periodically forces the photoconductive mode, ensuring fresh, accurate detection capability is restored regularly, while during dormant periods, the photovoltaic mode is maintained for power saving.
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 enables the use of the first frames acquired from a thin-film transistor (TFT) fingerprint sensor shortly after wake-up, improving usability by reducing pixel saturation and enhancing response time for fingerprint detection.
Implementation Method 1
each sensing pixel comprising a photodiode
Data Source
AI summary
An input device includes sensing pixels, each sensing pixel including a photodiode, and a gate driver circuit controlling operation of the sensing pixels. The gate driver circuit includes a set of cascaded gate driver units. Each of the cascaded gate driver units is associated with a subset of the sensing pixels, controlling an operation of the subset of the sensing pixels. The set of cascaded gate driver units output, during a reset phase of the input device, a global reset gate control signal to the sensing pixels in response to a clock signal. Each of the cascaded gate driver units sequentially output, during an operating phase of the input device, an operating gate control signal to the associated subset of the sensing pixels.