A circuit built using resistors and capacitors. The simplest are two-port networks that have one of each component-one in series with the input port and the other in parallel with the output. RC circuits are often used as filters. A low-pass filter will have the resistor in series with the input, and the capacitor in parallel with the output, while switching them around results in a high-pass filter. A band-pass filter can be obtained by connecting a low-pass filter to a high-pass filter. See also RLC circuit; RL circuit.