Apparatus and methods are provided for coupling RF signals. A lattice coupler design incorporating a pair of shunt inductors provides (i) a virtual ground for biasing and (ii) improved performance characteristics, in both splitter and combiner configurations. Magnetic coupling between the shunt inductors can be selected to maintain improved performance characteristics over a wide bandwidth, while retaining compactness and high efficiency. A design procedure, variations, and results are disclosed.

A nuclear magnetic resonance (NMR) power supply system and method are disclosed. The architecture adopts a two-stage topology to reduce the required capacitance by over ten times, leading to a four-fold improvement in power density. The first stage is an isolated converter that only supplies average power, therefore input filter and transformer sizes can be reduced. The second stage is a fast response DC-DC converter followed by a RF transmitter to produce a pulsed RF signal, so that the mid-point voltage after the first stage can be allowed to droop considerably, leading to much smaller sized capacitors. These and other embodiments enforce the isolated converter to only transfer average power, which reduces the power rating and the volume of the system's transformer.

Techniques for generating a power tracking supply voltage for a circuit (e.g., a power amplifier) are disclosed. The circuit may process multiple transmit signals being sent simultaneously on multiple carriers at different frequencies. In one exemplary design, an apparatus includes a power tracker and a power supply generator. The power tracker determines a power tracking signal based on inphase (I) and quadrature (Q) components of a plurality of transmit signals being sent simultaneously. The power supply generator generates a power supply voltage based on the power tracking signal. The apparatus may further include a power amplifier (PA) that amplifies a modulated radio frequency (RF) signal based on the power supply voltage and provides an output RF signal.

Techniques for generating a power tracking supply voltage for a circuit (e.g., a power amplifier) are disclosed. The circuit may process multiple transmit signals being sent simultaneously on multiple carriers at different frequencies. In one exemplary design, an apparatus includes a power tracker and a power supply generator. The power tracker determines a power tracking signal based on inphase (I) and quadrature (Q) components of a plurality of transmit signals being sent simultaneously. The power supply generator generates a power supply voltage based on the power tracking signal. The apparatus may further include a power amplifier (PA) that amplifies a modulated radio frequency (RF) signal based on the power supply voltage and provides an output RF signal.

A radio frequency front-end is disclosed having a first power amplifier (PA) having a first PA input and a first PA output, a second PA having a second PA input and a second PA output, and a low-noise amplifier (LNA) having an LNA output connected to a receive output terminal and an LNA input. An input 90° hybrid coupler has a first port input connected to a transmit terminal, a second port input connected to a fixed voltage node through an isolation impedance, a third port output connected to the first amplifier input and a fourth port output connected to the second amplifier input. An output 90° hybrid coupler has a first port output connected to a common terminal, a second port output connected to the LNA input, a third port input connected to the second PA output, and a fourth port input connected to the first PA output.

Described are concepts, systems and techniques for dividing a communication channel such that no single radio frequency (RF) power amplifier (PA) in a remote radio head (RRH) operates over an excessively wide frequency bandwidth. This allows efficient operation of the RF PA wherein each PA transmit path is tuned for operation at a respective one of a plurality of different center frequencies (f.sub.0, f.sub.0+Δf, . . . f.sub.0+(n−1)Δf where n is an integer corresponding to the number of RF PA transmit paths.

Aspects of the subject disclosure may include a Doherty amplifier that includes a carrier amplifier having an output terminal, an output network coupled to the output terminal, and a peaking amplifier, wherein the output network comprises a non-linear reactance component, and wherein the non-linear reactance component changes an effective impedance of a load presented to the carrier amplifier when the peaking amplifier is off. Other embodiments are disclosed.

Aspects of the subject disclosure may include a Doherty amplifier that includes a carrier amplifier having an output terminal, an output network coupled to the output terminal, and a peaking amplifier, wherein the output network comprises a non-linear reactance component, and wherein the non-linear reactance component changes an effective impedance of a load presented to the carrier amplifier when the peaking amplifier is off. Other embodiments are disclosed.

There is provided a RF-DAC that may include (i) a first PAM that includes a first group of first power amplifiers of different amplifications, (ii) a second PAM that includes a second group of second power amplifiers of different amplifications; (iii) a load that includes an output port and a transformer; (iv) power amplifiers control units, and a transformer control unit. During a cycle of operation (i) each one of the first and second PAMs is configured to receive one or more power amplifiers digital control signals and activate a single power amplifier per each of the first and second PAMS, (ii) the transformer control unit is configured to receive a transformer digital control signal and control a transformer parameter of the transformer, and (iii) the transformer is configured to receive a first PAM output signal and a second PAM output signal, and output a transformer output signal that reflects digital information represented by the one or more power amplifiers digital control signals and the transformer digital control signal.

According to one embodiment, a transformer-based in-phase and quadrature (IQ) includes a differential balun having a first inductor and a second inductor. The first inductor has a first input terminal and a first output terminal. The second inductor has a second input terminal and a second output terminal. Additionally, the IQ generator circuit includes a third inductor magnetically coupled with the first inductor. The third inductor has a first isolation terminal and a third output terminal. The IQ generator circuit also includes a fourth inductor magnetically coupled with the second inductor. The fourth inductor has a second isolation terminal and a fourth output terminal. The IQ generator circuit additionally includes a first transistor coupled to the first input terminal of the first inductor. Further, the generator circuit includes a second transistor coupled to the second input terminal of the second inductor. The first transistor, the second transistor, the first inductor, and the second inductor form a part of a differential amplifier.