Current driving device

What is this patent about?

’047 is related to the field of current driving devices, particularly those used as drivers for high-definition display panels such as organic EL (OLED) or LED displays. In these applications, maintaining uniform image quality requires precise control over the output currents across thousands of pixels. However, fabrication variations and the physical layout of driver ICs often lead to inconsistencies in transistor performance, making it difficult to ensure that every output terminal delivers an identical current for a given input signal.

The underlying idea behind ’047 is to overcome the slow response times of traditional current-copying circuits when dealing with very small reference currents. In standard calibration, a small current takes a significant amount of time to charge a storage capacitor to the required gate voltage. The invention introduces a pre-charging mechanism that uses a dedicated voltage source to rapidly jump-start the capacitor to a level near the target value, followed by a fine-tuning phase using the actual reference current to ensure absolute accuracy.

The claims of ’047 focus on a current output circuit architecture that transitions through three distinct operational states: a voltage supply mode, a current supply mode, and a current output mode. The independent claims specify a structure where a voltage holding circuit (typically a capacitor) is connected to a high-speed switch that selectively couples it to a first voltage supply. This allows the circuit to switch from a coarse voltage-driven charging state to a precise current-driven calibration state before finally outputting a stabilized current to the display terminals.

In practical implementation, the device utilizes a current-voltage converting part to generate a reference voltage that is proportional to the desired output current. This generated voltage is buffered and supplied to the output circuits during the initial phase of calibration. By using a replica circuit to estimate the necessary gate voltage, the system ensures that the pre-charge voltage is already extremely close to the final steady-state value, minimizing the workload of the reference current source during the subsequent fine-tuning step.

This approach differentiates itself from prior art by decoupling the charging speed from the magnitude of the reference current. While conventional drivers struggle to calibrate quickly when brightness levels (and thus currents) are low, the ’047 design maintains high-speed operation regardless of the current level. Furthermore, the system can perform a collective voltage supply to all output parts simultaneously during startup or when the reference current changes, preventing the visible display artifacts that occur when output terminals are updated one by one.