Correlated Double Sampling Pixel Front End for Accurate Current Sensing
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Solution Overview
Problem
Variations in drive transistor characteristics in display pixels can degrade image quality if not compensated for, necessitating a system and method for accurately measuring these characteristics.
Innovation Solution
A system and method utilizing a differential low-pass filter and integrator with mirroring capacitors and polarity-reversing switches to sense pixel currents through correlated double sampling, allowing for accurate measurement of drive transistor characteristics by canceling noise and stabilizing currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If drive transistor characteristics are not compensated for, then device complexity is reduced, but image quality degrades
Solution Approach 1:
The sensing circuit is divided into multiple functional blocks: a differential low-pass filter stage with reset switches, an integrator stage with mirroring capacitors, and a polarity-reversing switch. This segmentation allows each block to perform a specific function (filtering noise, integrating current, reversing polarity for correlated double sampling) thereby achieving accurate pixel current measurement while keeping each individual block relatively simple and manageable.
2Measurement precision
If correlated double sampling is implemented, then measurement precision improves, but device complexity increases
Solution Approach 1:
The circuit implements correlated double sampling through periodic action by sequentially performing two integration operations with opposite polarities. The polarity-reversing switch enables the integrator to first integrate the pixel current in one polarity, then reverse and integrate again in the opposite polarity. This periodic switching allows noise components to cancel out while the signal is preserved, achieving high measurement precision through time-sequential operations rather than complex simultaneous circuitry.
Solution Approach 2:
The integrator acts as an intermediary between the differential low-pass filter and the final measurement output. It accumulates the filtered current over time, converting small current variations into measurable voltage changes. The mirroring capacitors serve as intermediaries to transfer and store the integrated charge, enabling the correlated double sampling process to achieve high precision measurement while maintaining circuit simplicity.
3Stability of the object's composition
If reset switches are used in the low-pass filter, then stability improves during reset, but manufacturing precision may be affected by reset timing
Solution Approach 1:
The reset switches in the differential low-pass filter are activated before the integration process begins, preliminarily clearing any accumulated charge or noise in the filter stage. This preliminary reset action ensures that the filter starts from a known stable state, preventing residual signals from affecting the subsequent measurement. The timing is coordinated so that resetting occurs first, then integration begins, ensuring both stability and measurement accuracy.
Data Source
AI summary
A system and method for operating a sensing circuit for sensing a pixel current of a pixel of a display panel using correlated double sampling. In some embodiments, the method includes: during a first interval of time, resetting a pixel sensing circuit; during a third interval of time following the first interval of time, operating the pixel sensing circuit in an integration mode; during a fourth interval of time following the third interval of time, operating the pixel sensing circuit in a hold mode; and during a fifth interval of time following the fourth interval of time, operating the pixel sensing circuit in the integration mode.