Current Sensing Unit for OLED Displays with Dynamic Integration
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Solution Overview
Problem
Current sensing capability in large-area organic light-emitting displays is limited by the fixed input voltage range of ADCs, leading to underflow or overflow issues when dealing with high pixel currents, and increasing the feedback capacitor size is not feasible due to size constraints in the source driver IC.
Innovation Solution
A current sensing type sensing unit with a current sink circuit that reduces pixel current by a sink current, a current integrator that accumulates the adjusted current, a sampling part that holds the integrated value, and an ADC that converts this value to a digital signal, with a sink current control part that adjusts the sink current based on digital sensed values to maintain the integrated value within the ADC's range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the feedback capacitor size is increased to improve current sensing capability, then the sensing range is extended, but the source driver IC size increases beyond acceptable limits
Solution Approach 1:
The patent implements a dual-mode current integrator that dynamically switches between first and second integration modes based on the pixel current magnitude. In the first mode, a first feedback capacitor provides standard integration. In the second mode, a second feedback capacitor with larger capacitance value is activated to handle high pixel currents from large-area displays. This dynamic switching allows the system to adapt its sensing range without permanently increasing the IC footprint, as the larger capacitor is only activated when needed.
Solution Approach 2:
The patent changes the integration parameter (feedback capacitor value) based on the sensing requirements. By providing multiple feedback capacitors with different capacitance values and selectively activating them, the system can adjust its integration capacity to match the pixel current magnitude. This parameter change approach allows the same hardware to handle both small and large currents effectively without requiring a permanently large capacitor that would increase IC size.
2Device complexity
If the ADC input voltage range is fixed, then the device complexity is reduced, but the sensing capability is limited when pixel current increases in large-area displays
Solution Approach 1:
The patent employs a dual-mode current integrator that dynamically adjusts its integration behavior based on the pixel current magnitude. The controller switches between first and second integration modes, which produce different integrated voltage ranges. This dynamic adaptation allows the system to keep the integrated value within the fixed ADC input voltage range while maintaining accurate sensing capability across varying current levels, effectively resolving the contradiction between fixed ADC range and variable sensing requirements.
Data Source
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AI summary
A current sensing type sensing unit comprising: a current sink circuit (SINK) that is connected to a sensing line (14B) and reduces a pixel current (Ip) fed via the sensing line (14B) by an amount equal to a sink current (Is); a current integrator (CI) that is connected to the sensing line (14B) and accumulates an adjusted current (Ip-Is), which equals the pixel current (Ip) minus the sink current (Is), to produce an integrated value (Vsen); a sampling part (SH) that samples and holds the integrated value (Vsen); and an analog-to-digital converter (ADC) that performs analog-to-digital conversion of the integrated value (Vsen) from the sampling part (SH) to produce a digital sensed value (SD).