A high isolation duplexer/quasi circulator with two quadrature couplers is disclosed. Isolation between a transmit (TX) port and receive (RX) port of the quasi circulator is improved through use of two quadrature couplers. The quadrature couplers are coupled such that a first TX-RX signal path (from the TX port to the RX port) is shifted at or near 180 degrees from a second TX-RX signal path. These paths cancel each other to provide a high level of isolation between the TX port and the RX port. There are two signal paths between an antenna (ANT) port and the quadrature couplers for both TX signals and RX signals. A phase shift circuit is coupled to the ANT port of one or both duplexers such that the signals passing through the quadrature couplers to the ANT port are combined substantially in phase.

A radio frequency module includes a switch circuit that includes selection terminals, a filter that allows the signal in the first frequency band to pass therethrough, a filter that allows the signal in the second frequency band to pass therethrough, a phase adjustment circuit that is connected to the selection terminal and the filter, and a phase adjustment circuit that is connected to the selection terminal and the filter. The filter includes an acoustic wave resonator that is formed on a substrate that has piezoelectricity. The filter includes an acoustic wave resonator that is formed on a substrate that has piezoelectricity. At least one of circuit elements that are included in the phase adjustment circuit is formed on the substrate. At least one of circuit elements that are included in the phase adjustment circuit is formed on the substrate.

A high isolation duplexer/quasi circulator with two quadrature couplers is disclosed. Isolation between a transmit (TX) port and receive (RX) port of the quasi circulator is improved through use of two quadrature couplers. The quadrature couplers are coupled such that a first TX-RX signal path (from the TX port to the RX port) is shifted at or near 180 degrees from a second TX-RX signal path. These paths cancel each other to provide a high level of isolation between the TX port and the RX port. There are two signal paths between an antenna (ANT) port and the quadrature couplers for both TX signals and RX signals. A phase shift circuit is coupled to the ANT port of one or both duplexers such that the signals passing through the quadrature couplers to the ANT port are combined substantially in phase.

A radio frequency (RF) filter having a first passband and including a first circuit connected to a first node and a second node disposed on a path that connects a first terminal and a second terminal, and a second circuit connected to the first node and the second node. The first circuit includes a first filter having a second passband that includes a portion of a frequency range of the first passband and a bandwidth narrower than a bandwidth of the first passband. The second circuit includes a second filter having a third passband that includes a portion of a frequency range of the first passband and has a bandwidth narrower than the bandwidth of the first passband. The RF filter also includes a first phase shifter connected to a first terminal of the second filter; and a second phase shifter connected to a second terminal of the second filter.

A filter device provides a wideband passband of a communication device for a RF signal. The filter device includes a first filter circuit in parallel with a second filter circuit. The first filter circuit includes a first notch filter, and has a first notch. The second filter circuit includes a second notch filter in series with a reversal circuit for phase shifting the RF signal filtered by the second notch filter, the second filter circuit having a second notch. The first and second filter circuits form a band pass filter having a passband between a lower cutoff frequency defined by the second notch and an upper cutoff frequency defined by the first notch. The band pass filter provides low insertion loss in the passband, and high insertion loss in an adjacent lower stopband below the lower cutoff frequency and in an adjacent upper stopband above the upper cutoff frequency.

A filter device provides a wideband passband of a communication device for a RF signal. The filter device includes a first filter circuit in parallel with a second filter circuit. The first filter circuit includes a first notch filter, and has a first notch. The second filter circuit includes a second notch filter in series with a reversal circuit for phase shifting the RF signal filtered by the second notch filter, the second filter circuit having a second notch. The first and second filter circuits form a band pass filter having a passband between a lower cutoff frequency defined by the second notch and an upper cutoff frequency defined by the first notch. The band pass filter provides low insertion loss in the passband, and high insertion loss in an adjacent lower stopband below the lower cutoff frequency and in an adjacent upper stopband above the upper cutoff frequency.

A phase shifter having a four port hybrid coupler is provided. The four port hybrid coupler has first and second input ports and first and second output ports. The four port hybrid coupler is configured to shift the phase of an RF signal as between the first and second input ports. First and second active semiconductor devices are connected to first and second output ports. The first and second active semiconductor devices are configured to change the phase shift of the RF signal as between the first and second input ports based upon a varying voltage.

A phase shifter having a four port hybrid coupler is provided. The four port hybrid coupler has first and second input ports and first and second output ports. The four port hybrid coupler is configured to shift the phase of an RF signal as between the first and second input ports. First and second active semiconductor devices are connected to first and second output ports. The first and second active semiconductor devices are configured to change the phase shift of the RF signal as between the first and second input ports based upon a varying voltage.

A polyphase filter operates to provide capacitive compensation to drive a multiphase network for generating quadrature signals. The polyphase filter can include a capacitive compensation mechanism at internal nodes. The capacitive compensation mechanism includes a first phase lag circuit between a first internal node and a second internal node and a second phase lag circuit coupled between a third internal node and a fourth internal node. The first internal node is coupled to the second internal node via a first inductor coupled to a first resistor, the second internal node is coupled to the third internal node via a second inductor coupled to a second resistor, the third internal node is coupled to the fourth internal node via a third inductor coupled to a third resistor, and the fourth internal node is coupled to the first internal node via a fourth inductor coupled to a fourth resistor.

Various embodiments of the invention relate to a high performance analog bandpass filter (BPF) with improved performance in suppressing parasitic passband. The BPF comprises a first loss-pass filter (LPF) coupled to a first RF port, a second LPF coupled to a second RF port, and at least one high-pass module coupled in series between the first LPF and the second LPF for band-pass tuning. A resonant circuit is composed by a shunt capacitor from the LPF, a shunt inductor from the high-pass module and a series inductor from the LPF coupled in between. Such layout empowers the LPFs triple functions: to function as a low-pass filter, to participate in resonant circuit for center frequency tuning of the BPF, and to suppress parasitic resonance. Such a triple-function of the LPFs gives the BPF an improvement in a compact but effective topology.