For this reason, most modern line codes are designed to produce DC-balanced waveforms. The most common classes of DC-balanced line codes are constant-weight codes and paired-disparity codes. Gimmick loop A gimmick loop is a simple type of capacitive coupler: two closely spaced strands of wire. It provides capacitive coupling of a few picofarads between two nodes. Usually the wires are twisted together. Parasitic capacitive coupling Capacitive coupling is often unintended, such as the capacitance between two wires or PCB traces that are next to each other. One signal may capacitively couple with another and cause what appears to be noise. To reduce coupling, wires or traces are often separated as much as possible, or ground lines or ground planes are run in between signals that might affect each other, so that the lines capacitively couple to ground rather than each other. Prototypes of high-frequency (tens of megahertz) or high-gain analog circuits, often use circuits that are built over a ground plane to control unwanted coupling. If a high-gain amplifier's output capacitively couples to its input it may become an electronic oscillator. See also Coupling (electronics) DC block Decoupling (electronics) Decoupling capacitor Direct coupling Differential capacitance RC coupling Crosstalk References External links Howard Johnson: When to use AC coupling, DC Blocking Capacitor Value Texas Instruments: AC-Coupling Between Differential LVPECL, LVDS, HSTL, and CML (PDF) Capacitors Electromagnetic compatibility