Switchless half-duplex transceiver front end

摘要

In a half-duplex transceiver used in mobile terminals such as cell phones, hand-held cellular terminals and laptop computers that require two antennas, switches used to select the antennas may be eliminated. Instead a bias current is used to condition a PA and LNAs associated with antennas to create the communication path. In a system with two antennas for receiving and one PA for transmitting the front end is designed so that it is possible to receive through either of the antennas or transmit through one antenna without having switches in the signal paths to direct the signal. During transmission the bias currents of the LNAs associated with antennas are turned off and the input impedance of one LNA is such that the output power of the PA is directed to an antenna. In a receiving state only one of the LNAs is used and the PA bias is turned off. A receive path for a selected antenna is chosen by turning on one of the LNAs. The PA's impedance is such that if receiving through the selected antenna the power is directed to the LNA input associated with it. The same method is applied to in LNA outputs. A BT (Bluetooth) module may be used in the system by providing access through a switch S1 to an antenna. <IMAGE>