| 摘要 |
<p>A number of high isolation switching circuits for selectively connecting a common antenna port to a TX port 2 or an RX port 3 of a multi-band cellular handset are described. One such circuit (fig. 5) includes first and second PIN diodes D1 and D2, the first diode D1 having its anode connected to the TX port 2 and its cathode connected to a first node X, which is connected both to the antenna port and to one side of a phase shifting network P1. The other side of the phase shifting network is connected, via a first impedance transformation device (transformer) T1, to a second node Y. The second diode D2 has its anode connected to the second node Y and its cathode connected to ground via a resonant circuit L1/C1, and the second node Y is connected to the RX port 3 via a second impedance transformation circuit T2. The first impedance transformation circuit T1 lowers the impedance of the circuit at the second node Y when measured at the first node X and the second impedance transformation circuit T2 raises the impedance of the RX port when measured at the second node Y. In other circuits (figs. 9 and 10) there are three PIN diodes, the first diode being connected as stated above, and the second and third diodes being connected in parallel to the second node. <IMAGE></p> |
