A Micro-LED Pixel Circuit Using Capacitor-Coupled Current Control and Pulse-Width Modulation

This paper proposes a p-type low-temperature polycrystalline silicon (LTPS) pixel circuit for driving micro light-emitting diode ( $\mu $ LED) displays. Using pulse width modulation (PWM) is crucial to prevent wavelength shifts due to driving current variations. Maximizing emission time results in reducing maximum LED current, which may additionally reduce power consumption. The proposed circuit features one horizontal line time of $3.0~\mu $ s, enabling $\mu $ LEDs to emit for 85.9% of a frame time. A capacitive coupling effect is utilized to generate a constant current, eliminating the need for an external reference voltage or data voltage. Simulation results confirm that the pulse width of $\mu $ LED emission is modulated by the data voltage, ensuring stable PWM operation. Furthermore, the average current deviation in a frame stayed within only 1.54% under threshold voltage ( ${\mathrm{V}}_{\mathrm {TH}}$ ) shift of ±0.5 V in the range of G31 to G255. When capacitance variation is ±5%, the average current deviation ranged only from −2.9% to 2.8% in a frame. Simulation results confirm the proposed pixel circuit’s operation is robust against variations in VTH and capacitance.