Coupled-line baluns with common-mode compensation are provided herein. In certain configurations, a series resistor-inductor (RL) network is connected to ports of a coupled-line balun to null the common-mode transmission coefficient at a desired frequency. This extends performance at lower frequencies by improving the low frequency amplitude and phase balance of the device. The inductor and resistor can be connected in series between one of the differential terminals and a single-ended grounded terminal. This advantageously can null the common-mode transmission at a specific frequency near a minimum length-dominated frequency so as to enhance the common-mode rejection at lower frequencies.

A balun circuit is disclosed. The balun circuit is provided between a transmitter and a common antenna terminal to which the transmitter and a receiver are coupled. The balun includes an inductor L1 coupled at one or both ends to the transmitter, an input node of the receiver, and an inductor L2 provided between ground or a first biasing power supply. The inductor L2 includes an inductor having a mutual inductance with the inductor L1. The inductor L2 is a variable inductor.

A small-sized balance filter includes an unbalanced terminal and two pairs of balanced terminals and has a low signal insertion loss. An unbalanced terminal, a first balanced terminal including first and second terminals, and a second balanced terminal Rx including first and second terminals are provided. An unbalanced-side inductor is provided between the unbalanced terminal and the ground, first balanced-side inductors are provided between the first and second terminals of the first balanced terminal, second balanced-side inductors are provided between the first and second terminals of the second balanced terminal, and the unbalanced-side inductor is electromagnetic-field-coupled to each of the first and second balanced-side inductors.

A transmission line transformer having a time delay network having a signal terminal and a pair of output terminals connected to the signal terminal through a corresponding one of a pair of time delay elements, the delay line elements having different time delays. A pair of transmission lines, each one having a pair of electrically coupled elements. A first one of the elements in one of the transmission lines has a first end connected to one of the pair of output terminals. A second one of the elements in such one of the transmission lines has a second end connected to a second end of one of the pair of elements in the other one of the transmission lines. The first one of the pair of elements in the other one of the pair of transmission lines is coupled to a second one of the pair of output terminals.

The disclosure relates to a circuit comprising a balun portion, a balanced side impedance transforming element and an unbalanced side impedance transforming element. The balun portion at least partly transforms the signal between a balanced signal input/output terminal and an unbalanced signal input/output terminal. The impedance transforming elements at least partly alter the impedance presented at the balanced and unbalanced side of the balun. In addition at least one matching transmission element is provided. By separating the role of impedance transformation from balun signal conversion, the useful bandwidth of the circuit can be improved in comparison to a balun that provides both signal conversion and impedance transformation functions.

A balun includes an unbalanced port, a first balanced port, a second balanced port, a main line, a subline, a capacitor, and an impedance matching section. The subline is configured to be electromagnetically coupled to the main line. The main line has a first end and a second end opposite to each other. The subline has a first end and a second end opposite to each other. The capacitor is provided between the first end of the main line and the unbalanced port. The impedance matching section is provided between the second end of the subline and the second balanced port. The second end of the main line is connected to a ground. The first end of the subline is connected to the first balanced port.

Coupled-line baluns with common-mode compensation are provided herein. In certain configurations, a series resistor-inductor (RL) network is connected to ports of a coupled-line balun to null the common-mode transmission coefficient at a desired frequency. This extends performance at lower frequencies by improving the low frequency amplitude and phase balance of the device. The inductor and resistor can be connected in series between one of the differential terminals and a single-ended grounded terminal. This advantageously can null the common-mode transmission at a specific frequency near a minimum length-dominated frequency so as to enhance the common-mode rejection at lower frequencies.

A transformer-based balun circuit s disclosed herein. The balun can be implemented using a spiral transformer, where primary and secondary transformer windings can be inductively coupled and can be implemented on the same metal layer (or different metal layers, e.g. vertically adjacent metal layers). The balun can further include a compensation capacitor and a digital frequency tuning circuit. The compensation capacitor can be introduced at one of the differential terminals to reduce or suppress the amplitude and phase imbalance. The digital frequency tuning circuit can be a switchable bank of capacitors, which allows for tuning the frequency of operation of the transformer-based balun.

The disclosure relates to a circuit comprising a balun portion, a balanced side impedance transforming element and an unbalanced side impedance transforming element. The balun portion at least partly transforms the signal between a balanced signal input/output terminal and an unbalanced signal input/output terminal. The impedance transforming elements at least partly alter the impedance presented at the balanced and unbalanced side of the balun. In addition at least one matching transmission element is provided. By separating the role of impedance transformation from balun signal conversion, the useful bandwidth of the circuit can be improved in comparison to a balun that provides both signal conversion and impedance transformation functions.

A power amplifier cell (401) comprising: a first power amplifier (410), a second power amplifier (416) and a balun (422). The balun (422) comprising: a first transmission line (430); a second transmission line (432); a third transmission line (434); a fourth transmission line (436); and a biasing circuit (438) connected between (i) a reference terminal, and (ii) a second end of the second transmission line and a second end of the fourth transmission line.