In LED displays, the brightness of an LED is realized via a PWM that is individually set for the respective LED. As a result, the spectrum of the radiated interference power has high values at the fundamental wave of the PWM frequency. Furthermore, a large range of the variable duty cycle is visible to the human eye.

This is remedied by so-called spread spectrum PWMs, in which the pulse is broken down into fragments and distributed over the PWM period. For example, a duty cycle of 50% becomes "5 times 10% on / 10% off" from "50% on / 50% off".

For LED control of an LED display panel controller, we implemented a spread spectrum PWM.

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Concept and implementation of the FPGA design.

Used technologies

  • Xilinx Spartan 6
  • VHDL
  • SPI
  • Spread-PWM

Used tools

  • Xilinx ISE
  • GHDL
  • Doxygen