PIN diodes, or P-type Intrinsic-N diodes, are a type of diode composed of a semiconductor material with a p-type layer, an intrinsic layer, and an n-type layer. They are used primarily for switching and controlling high frequency signals, and can also be used as detectors and attenuators. They operate at frequencies of up to several hundred GHz, and feature low capacitance and high-frequency response. PIN diodes are typically used in RF circuits, especially in cell phones, WiFi and satellite systems, radar systems, and amplifier modulation. They are also used in filtering, switching, and amplitude control in radio frequency (RF) and high-frequency (HF) communications systems.