Evidence of long-range interactions between logic transitions in unclocked FPGA circuits is reported. The relative positions of pulses traveling in digital feedback loops are observed to dynamically interact and move to equal spacing over long timescales. We confirm the presence of this interaction over different FPGA supply voltages and hypothesize the pulse interactions are due to current draw in the power distribution network of the FPGA. This pulse interaction effect is observed for different FPGA families and manufacturers, including Altera and Xilinx, and has been tested using both look-up table (LUT) and carry chain (CC) logic to realize the feedback delays.INDEX TERMS asynchronous circuits, feedback circuits, field-programmable gate arrays, pulse circuits, pulse interactions, non-blocking delay lines, oscillators, network dynamics, transient analysis.