MULTIPLEXER AND FRONTEND MODULE COMPRISING A MULTIPLEXER
A multiplexer circuit with good isolation characteristics and a compensated frequency characteristic at the transmission side is presented. The multiplexer circuit has a reception filter notch circuit (RFNC) active at a frequency within a passband of a reception filter (RXF) and coupled between an input port and a transmission filter (TXF).
1 . A multiplexer circuit comprising
an input port, a common port, an output port and a signal line between the input port and the common port,
a transmission filter between the input port and the common port,
a reception filter coupled to the output port,
a reception filter notch circuit coupled between the input port and the transmission filter, wherein
the reception filter has a passband and
the reception filter notch circuit is active at a frequency within the passband of the reception filter.
2 . The multiplexer of claim 1 , wherein the reception filter comprises a capacitive element.
3 . The multiplexer of claim 2 , wherein the capacitive element of the reception filter notch circuit electrically connects the signal line to ground.
4 . The multiplexer of claim 1 , wherein the reception filter notch circuit is provided to create a notch in the transfer function S 21 .
5 . The multiplexer of claim 1 , wherein
the multiplexer is a duplexer and the transmission filter and the reception filter are filters of the duplexer, or
the multiplexer is a multiplexer of a degree higher than 2, and the multiplexer comprises an additional reception filter.
6 . The multiplexer of claim 1 , wherein the reception filter notch circuit improves reception cross isolation in a carrier aggregation system.
7 . The multiplexer of claim 1 , further comprising an impedance matching circuit between the input port and the transmission filter.
8 . The multiplexer of claim 1 , further comprising
a power amplifier connected to the input port and the transmission filter and/or
a low noise amplifier connected to the output port.
9 . A frontend module, comprising the multiplexer of claim 1 and a power amplifier, wherein the circuit elements of the multiplexer and the circuit elements of the power amplifier are combined in a single component.