A wireless communication unit (200) comprises a radio frequency (RF) receiver for receiving an RF signal and providing the received RF signal to an off-channel signal detector (218) and a quadrature down conversion mixer circuit comprising at least one dynamic matching mixer stage (226, 228, 250, 252). The off-channel signal detector (218) is arranged to detect whether an off-channel signal level of the received RF signal exceeds a threshold and, in response to determining that the received off-channel RF signal exceeds the threshold, the off-channel signal detector (218) deactivates the at least one dynamic matching mixer stage. Also described is a semiconductor that comprises a receiver, and a method of operation therefor.