Aspects of this disclosure relate to a band pass filter that includes LC resonant circuits coupled to each other by a capacitor. A bridge capacitor can be in parallel with series capacitors, in which the series capacitors include the capacitor coupled between the LC resonant circuits. The bridge capacitor can create a transmission zero at a frequency below the passband of the band pass filter. The LC resonant circuits can each include a surface mount capacitor and a conductive trace of the substrate, and an integrated passive device die can include the capacitor. Band pass filters disclosed herein can be relatively compact, provide relatively good out-of-band rejection, and relatively low loss.

A power amplifier circuit includes a power amplifier that amplifies an input signal and outputs the amplified signal from an output terminal thereof, a first filter circuit that has a frequency characteristic that attenuates an Nth-order harmonic of the amplified signal, N that is an integer greater than or equal to 2, and a second filter circuit that has a frequency characteristic that attenuates the Nth-order harmonic of the amplified signal. The first filter circuit includes a first capacitor and a first inductor. The first capacitor and the first inductor are connected in series between the output terminal and ground. The second filter circuit includes a second capacitor and a second inductor. The second capacitor and the second inductor are connected in series between the output terminal and ground.

A filter module includes a filter provided on a path connecting an input/output terminal and an input/output terminal, a filter provided on a path connecting an input/output terminal and an input/output terminal, a switch that switches between electrical connection and electrical disconnection between a wire connected to the input/output terminal and a ground, and a switch that switches between electrical connection and electrical disconnection between a wire connected to the input/output terminal and the ground. When the wire and the ground are electrically connected by the switch, the wire and the ground are electrically disconnected by the switch, and when the wire and the ground are electrically connected by the switch, the wire and the ground are electrically disconnected by the switch.

In certain aspects, a method is provided for measuring power using a resistive element coupled between a power amplifier and an antenna. The method includes squaring a voltage from a first terminal of the resistive element to obtain a first signal, squaring a voltage from a second terminal of the resistive element to obtain a second signal, and generating a measurement signal based on a difference between the first signal and the second signal. In some implementations, the resistive element is implemented with a power switch.

A system for split-frequency amplification, preferably including: one or more primary-band amplification stages, one or more secondary-band amplification stages, one or more band-splitting filters, and/or one or more signal couplers. An analog canceller including one or more split-frequency amplifiers. A mixer including one or more split-frequency amplifiers. A voltage-controlled oscillator including one or more split-frequency amplifiers. A method for split-frequency amplification, preferably including: receiving an input signal, separating the input signal into signal portions, and/or amplifying the signal portions, and optionally including combining the amplified signal portions and/or providing one or more output signals.

A filter combiner for a Doherty amplifier includes a first port with an impedance of Z0 configured to be connected to an output of a carrier amplifier; a second port with an impedance of Z0.Math.r/(1+r) configured to be connected to a load; a third port with an impedance of Z0.Math.r/(1+r) configured to be connected to a peak amplifier, wherein r is a power ratio for the carrier amplifier to the peak amplifier; and a fourth port with an impedance of Z0 configured to be connected to an output port of the Doherty amplifier. The first port is connected to the second port via a first network that is a lowpass filter and to the third port via a second network that is a lowpass filter which is configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The third port is connected to the fourth port via a third network that is a lowpass filter configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The fourth port is connected to the second port via a fourth network that is a lowpass filter.

Bulk acoustic wave resonators of two or more different filters can be on a common die. The two filters can be included in a multiplexer, such as a duplexer, or implemented as standalone filters. With bulk acoustic wave resonators of two or more filters on the same die, the filters can be implemented in less physical space compared to implementing the same filters of different die. Related methods, radio frequency systems, radio frequency modules, and wireless communication devices are also disclosed.

A radio frequency module includes: a module board including a first principal surface and a second principal surface on opposite sides of the module board; an antenna connection terminal; a diplexer connected to the antenna connection terminal and including at least a first inductor which is a chip inductor; a transmission power amplifier; and a first circuit component disposed on a transmission path connecting the diplexer and the transmission power amplifier. The first inductor is disposed on the first principal surface, and one of the transmission power amplifier and the first circuit component is disposed on the second principal surface.

Provided are a power amplifier circuit and a communication device that improve a power handling capability required for a filter while increasing output power. A power amplifier circuit includes: an amplifier unit that amplifies an input signal of a time division duplex scheme and outputs a signal to a signal path and a signal to a signal path; a filter that is provided in the signal path and outputs a signal based on the signal; a filter that is provided in the signal path and outputs a signal based on the signal; and a transformer that is connected to the signal path through the filter and connected to the signal path through the filter and outputs an output signal based on the signal and the signal to a signal path.

Apparatus and methods remove a voltage offset from an electrical signal, specifically a biomedical signal. A signal is received at a first operational amplifier and is amplified by a gain. An amplitude of the signal is monitored, by a first pair of diode stages coupled to an output of the first operational amplifier, for the voltage offset. The amplitude of the signal is then attenuated by the first pair of diode stages and a plurality of timing banks. The attenuating includes limiting charging, by the first pair of diode stages, of the plurality of timing banks and setting a time constant based on the charging. The attenuating removes the voltage offset persisting at a threshold for a duration of at least the time constant. Saturation of the signal is limited to a saturation recovery time while the saturated signal is gradually pulled into monitoring range over the saturation recovery time.