Five-Transistor Pixel Circuit for OLED Threshold Compensation

The patent combines multiple functions into fewer transistors. Specifically, the write transistor and switch transistor are merged into a single transistor that performs both writing and switching operations. The compensation transistor and drive transistor are integrated such that the drive transistor itself performs threshold compensation through its operation in the saturation region, eliminating the need for a separate compensation transistor. This merging reduces the transistor count from six or more to five transistors per pixel while maintaining threshold compensation capability.

The patent makes transistors perform multiple functions. The drive transistor serves dual purposes: it acts as the primary drive transistor for controlling the light emitting element and simultaneously functions as the compensation transistor for threshold voltage compensation. The first scanning signal line serves multiple purposes by controlling both the write transistor and the merged write/switch transistor at different timing phases. This multi-functionality reduces the overall transistor count while maintaining all necessary functions.

The patent performs threshold compensation preliminarily through the drive transistor's operation characteristics. By designing the drive transistor to operate in the saturation region during the light emission period, the transistor naturally exhibits square-law characteristics that are independent of threshold voltage variations. The compensation is achieved preliminarily through proper biasing and timing control, where the drive transistor's gate-source voltage is maintained at a level that ensures saturation operation, thereby compensating for threshold variations without requiring additional active compensation transistors.

The patent changes the operating parameters of the drive transistor to achieve compensation. Specifically, it controls the drive transistor to operate in the saturation region by maintaining appropriate gate-source and drain-source voltage relationships. The patent also utilizes capacitive coupling and specific timing sequences to maintain the drive transistor in the desired operating region, where the current becomes independent of threshold voltage variations. This parameter-based approach allows compensation with fewer transistors.