Abstract: A coupling circuit for a bus subscriber on a bus line of a field bus with DC-voltage-free and differential EIA-485/EIA-422-compliant signal transmission according to a TTP protocol, in which the two inputs/outputs of a transmission/reception component of the bus subscriber are connected to a first winding of a signal transformer, and the two poles of the bus line are connected to a second winding of the signal transformer, and the first winding has a center tap, wherein the center tap is connected to the local reference-earth potential of the bus subscriber via a capacitor, the capacitance of which is at least 100 times the parasitic capacitance of the transformer.