Investigating LED Matrix Ghosting at Row Transitions

A multiplexed LED matrix can show faint light in pixels commanded off when the active row changes. The unwanted light may result from charge stored in the matrix and switching paths rather than incorrect image data. Correlate the optical event with electrical timing before correcting it in the image map.

Separate data errors from transition light

Display a sparse pattern with one bright pixel or row against a dark background. Note whether the unwanted light follows a neighboring row, a particular column, or a particular data value. Compare steady illumination with light concentrated around row changes.

The TI LP5890 data sheet describes dedicated functions addressing upper and lower ghosting in multiplexed LED applications. Such features are device specific; their configuration should follow the selected driver’s timing and matrix arrangement.

Capture the switching sequence

Observe row drive, column output, and a suitable optical detector together. Mark the previous row turning off, any blank interval, and the next row turning on. Use a detector and measurement bandwidth capable of resolving the unwanted pulse.

Check whether two row paths overlap or whether an inactive node retains charge. A logic level showing that a row switch is commanded off does not by itself establish that the LED current has stopped at the same instant.

Evaluate supported timing controls

Adjust blanking, precharge, discharge, or deghosting settings only within the supported configuration. Change one parameter at a time and record the electrical and optical effect. The appropriate adjustment depends on the path causing the pulse.

Longer blanking can reduce available illumination time, so compare brightness and low grayscale behavior as well as ghosting. Avoid compensating for lost duty by increasing peak current beyond the reviewed LED and driver operating conditions.

Test difficult patterns and operating conditions

Include isolated bright pixels, alternating bright and dark rows, rapid image changes, and low grayscale patterns. Check relevant supply and temperature conditions because node capacitance, LED voltage, and switching behavior can change the visible result.

Save matrix wiring, scan ratio, timing configuration, optical detector arrangement, and representative captures. Define an acceptance method that can distinguish a brief transition pulse from sustained leakage. A successful correction removes the unwanted light mechanism while preserving intended brightness and grayscale response. Editing pixel data until one photograph looks clean does not establish that the electrical row transition is correct across other patterns, exposure settings, or display operating modes. Keep the optical detector position unchanged between timing experiments.