Design of an Application-Specific Instruction-Set Processor-based Configurable LED Panel Controller

Abstract

Light-emitting diodes (LEDs) have attracted attention for their use in large-scale display panels. LEDs have advantages such as power efficiency, high brightness, long life, and eco-friendliness. Naturally, the use of LED display systems has increased significantly on the streets and indoors owing to their use as engaging and effective information-display panels. Applications for LED display systems include high-quality scoreboards in sports stadiums, large screens in concert halls, and video signboards on the exterior walls of commercial buildings. The sizes, resolutions, and aspect ratios of these LED display systems depend on the intended application. High-resolution LED displays are composed of a number of LED panels and can be easily changed these resolution and aspect ratio by rearranging LED panels. An LED panel is driven by an LED controller which generally employs a pulse width modulation (PWM) to display images. However, the PWM-based control has two main concerns: flickering and inrush current. In order to avoid flickering, it is required to use a high-speed controller. On the other hand, the inrush current problem that occurs when many LED pixels are driven simultaneously can be avoided by spreading out the peak current. Conventional sophisticated LED controllers have been designed to provide high-operating speed to alleviate flickering phenomenon. However, these controllers do not consider changing the structure of the LED panels and PWM schemes of the LED panels. There are various PWM schemes and new algorithms are still being proposed. Accordingly, the LED controller requires flexibility when implementing its PWM scheme to replace algorithm with the state-of-the-art PWM scheme without having to redesign the its hardware. Frequent changes to the LED panel structure also require the flexibility of the LED controller. Microprocessor-based controllers are one solution to provide the necessary flexibility. However, these controllers do not guarantee real-time operation. This dissertation proposes a new LED controller that consists of an application-specific instruction-set processor (ASIP) and custom hardware modules. The ASIP of the proposed LED controller provides a specialized architecture for flexibility in control scheme as well as the real-time operation without flickering. The proposed LED controller separately stores the LED pixel data in different memory banks corresponding to given position in each of the binary numbers, that is fast and convenient to handle the data used to represent the gray levels using PWM methods. Moreover, the proposed controller also uses a custom hardware module to automatically generates a sequence of memory addresses while considering the display resolution for the LED data and to reduce data preparation time. The proposed LED controller was implemented as a prototype on a Xilinx Viertex-5 field-programmable gate array (FPGA) platform. The prototype of the proposed LED controller ran at 100 MHz, and it successfully drove three types of LED panels having 64 × 96, 96 × 80, and 128 × 64 pixels at refresh rates of 3,125, 2,232, and 1,736 Hz, respectively. In addition, the proposed LED controller could drive 1.44 times more pixels per unit time at the same refresh rate compared with the state-of-the-art hard-wired type LED controller.