A wideband low power active isolator that may operate with a low voltage supply and provide improved linearity and insertion loss is described. The active isolator includes parallel connected common gate amplifier and common drain amplifier that are implemented using active transistors. A RF choke configured to suppress RF signal is coupled between input to the common gate amplifier and the ground such that the common gate amplifier also functions as a current source biasing the common drain amplifier.

A wideband low power active isolator that may operate with a low voltage supply and provide improved linearity and insertion loss is described. The active isolator includes parallel connected common gate amplifier and common drain amplifier that are implemented using active transistors. A RF choke configured to suppress RF signal is coupled between input to the common gate amplifier and the ground such that the common gate amplifier also functions as a current source biasing the common drain amplifier.

Some embodiments of the application provide a filter circuit that is based on a MOS field effect transistor and a chip including the same. The filter circuit includes a first MOS field effect transistor and an electrostatic discharge unit; a gate of the first MOS field effect transistor and a substrate form a filter capacitance during normal operation; the electrostatic discharge unit and the first MOS field effect transistor form a discharge path that transfers aggregated electrostatic charges to ground when an ESD event occurs. On the basis of the first MOS field effect transistor, it is added to some embodiments of the present application an electrostatic discharge unit, which combines a capacitance characteristic and a characteristic of the ESD discharge path between the power supply and the ground to the same circuit, so that the circuit presents the capacitance characteristic during normal operation; an ESD discharge path is provided when an ESD event occurs between the power supply and the ground, which plays a role of ESD protection, thereby enhancing the ESD capability of the chip.

A circuit for driving a switched transistor comprises: a level shifter comprising at least one transistor, the level shifter configured to convert an input pulse to a pulse having a greater voltage swing than the input pulse and shift a voltage level of the converted pulse; and a pulse shaping filter coupled between the level shifter and the gate of the switched transistor, the pulse shaping filter tuned to cancel or reduce an impedance of the gate of the switched transistor. The switched transistor and/or the at least one transistor are a GaN High Electron Mobility Transistor (HEMT).

A technique for attenuating common mode transient events uses a differential receiver circuit including a band-stop filter having a stopband f.sub.SB around a notch frequency f.sub.n of a received signal. The differential receiver circuit includes a first high-pass filter coupled in series with the band-stop filter. The notch frequency f.sub.n is less than a carrier frequency f.sub.c of a signal received by the differential receiver circuit. The band-stop filter may include a buffer circuit and a notch filter coupled in series with the buffer circuit. The notch filter may have a second stopband around the notch frequency f.sub.n. The differential receiver circuit may have a propagation delay that is independent of a pulse width of common mode transient energy attenuated by the differential receiver circuit.

A technique for attenuating common mode transient events uses a differential receiver circuit including a band-stop filter having a stopband f.sub.SB around a notch frequency f.sub.n of a received signal. The differential receiver circuit includes a first high-pass filter coupled in series with the band-stop filter. The notch frequency f.sub.n is less than a carrier frequency f.sub.c of a signal received by the differential receiver circuit. The band-stop filter may include a buffer circuit and a notch filter coupled in series with the buffer circuit. The notch filter may have a second stopband around the notch frequency f.sub.n. The differential receiver circuit may have a propagation delay that is independent of a pulse width of common mode transient energy attenuated by the differential receiver circuit.

A technique for attenuating common mode transient events uses a differential receiver circuit including a band-stop filter having a stopband f.sub.SB around a notch frequency f.sub.n of a received signal. The differential receiver circuit includes a first high-pass filter coupled in series with the band-stop filter. The notch frequency f.sub.n is less than a carrier frequency f.sub.c of a signal received by the differential receiver circuit. The band-stop filter may include a buffer circuit and a notch filter coupled in series with the buffer circuit. The notch filter may have a second stopband around the notch frequency f.sub.n. The differential receiver circuit may have a propagation delay that is independent of a pulse width of common mode transient energy attenuated by the differential receiver circuit.

A technique for attenuating common mode transient events uses a differential receiver circuit including a band-stop filter having a stopband f.sub.SB around a notch frequency f.sub.n of a received signal. The differential receiver circuit includes a first high-pass filter coupled in series with the band-stop filter. The notch frequency f.sub.n is less than a carrier frequency f.sub.c of a signal received by the differential receiver circuit. The band-stop filter may include a buffer circuit and a notch filter coupled in series with the buffer circuit. The notch filter may have a second stopband around the notch frequency f.sub.n. The differential receiver circuit may have a propagation delay that is independent of a pulse width of common mode transient energy attenuated by the differential receiver circuit.

Some embodiments of the application provide a filter circuit that is based on a MOS field effect transistor and a chip including the same. The filter circuit includes a first MOS field effect transistor and an electrostatic discharge unit; a gate of the first MOS field effect transistor and a substrate form a filter capacitance during normal operation; the electrostatic discharge unit and the first MOS field effect transistor form a discharge path that transfers aggregated electrostatic charges to ground when an ESD event occurs. On the basis of the first MOS field effect transistor, it is added to some embodiments of the present application an electrostatic discharge unit, which combines a capacitance characteristic and a characteristic of the ESD discharge path between the power supply and the ground to the same circuit, so that the circuit presents the capacitance characteristic during normal operation; an ESD discharge path is provided when an ESD event occurs between the power supply and the ground, which plays a role of ESD protection, thereby enhancing the ESD capability of the chip.

Several embodiments of an envelope tracking active circulator is disclosed with a method to cascade them. In an active transistor based circulator (active circulator), gate (base) and drain (collector) bias voltage can be adjusted by RF or microwave input envelop signal. This is called envelop tracking active circulator. In this concept, input RF signal is detected by detection circuit, such as detection diode or coupler and converted into low frequency envelop signal by the proper filtering circuitry. The generated envelop signal controls the supply voltage of the drain and gate with the proper function of the envelop signal to improve active circulator insertion loss, isolation and power handling capability. This concept can be applied to any type of solid-state FET (Field effect transistor) transistor based active circulator, as long as they have bias dependent trans-conductance and capacitances inside. For a BJT (bipolar junction transistor) based active circulator, base bias current supply modulator will be used instead of voltage supply modulator.