An apparatus includes a radio-frequency (RF) apparatus, and a multi-band matching balun coupled to the RF apparatus. The multi-band matching balun including a plurality of capacitors and a plurality of inductors. None of the plurality of capacitors and none of the plurality of inductors is variable or tunable.

A frequency divider includes a signal injection circuit and an oscillating circuit. The signal injection circuit includes a transistor of which a gate receives an input signal with an input frequency, a drain and a source cooperatively provide a first differential signal pair, and a body receives a biasing voltage. The two circuits cooperate to form a tank circuit having a free-running frequency and defining a frequency locking range which is around N times the free-running frequency and within which the input frequency falls. The tank circuit generates a second differential signal pair that is related to the first differential signal pair and that has an oscillating frequency which is one-N.sup.th the input frequency.

A frequency divider includes a signal injection circuit and an oscillating circuit. The signal injection circuit includes a transistor of which a gate receives an input signal with an input frequency, a drain and a source cooperatively provide a first differential signal pair, and a body receives a biasing voltage. The two circuits cooperate to form a tank circuit having a free-running frequency and defining a frequency locking range which is around N times the free-running frequency and within which the input frequency falls. The tank circuit generates a second differential signal pair that is related to the first differential signal pair and that has an oscillating frequency which is one-N.sup.th the input frequency.

An apparatus, a system, and a communication device. The apparatus includes a substrate and a circuit formed on the substrate. The circuit includes a first transformer having first input nodes and first output nodes. The circuit further includes a second transformer having second input nodes and second output nodes. The first input nodes of the first transformer and the second input nodes of the second transformer are connected. At least one first output node of the first output nodes of the first transformer and at least one second output node of the second output nodes of the second transformer are connected. The circuit further includes a first capacitor connected to one of the first output nodes of the first transformer and to one of the second output nodes of the second transformer. The first capacitor is connected to a first ground.

An apparatus, a system, and a communication device. The apparatus includes a substrate and a circuit formed on the substrate. The circuit includes a first transformer having first input nodes and first output nodes. The circuit further includes a second transformer having second input nodes and second output nodes. The first input nodes of the first transformer and the second input nodes of the second transformer are connected. At least one first output node of the first output nodes of the first transformer and at least one second output node of the second output nodes of the second transformer are connected. The circuit further includes a first capacitor connected to one of the first output nodes of the first transformer and to one of the second output nodes of the second transformer. The first capacitor is connected to a first ground.

A matching circuit in a communication apparatus may comprise a first inductor disposed at a primary side of a transformer; a second inductor disposed at a secondary side of the transformer; and an impedance element connected to the first inductor and the second inductor. Also, a first terminal of the first inductor may be connected to an input terminal of the transformer, a second terminal of the first inductor may be connected to a common node connected to a ground, a first terminal of the second inductor may be connected to an output terminal of the transformer, a second terminal of the second inductor may be connected to the common node, a first terminal of the impedance element may be connected to the common node, and a second terminal of the impedance element may be connected to the ground.

A matching circuit in a communication apparatus may comprise a first inductor disposed at a primary side of a transformer; a second inductor disposed at a secondary side of the transformer; and an impedance element connected to the first inductor and the second inductor. Also, a first terminal of the first inductor may be connected to an input terminal of the transformer, a second terminal of the first inductor may be connected to a common node connected to a ground, a first terminal of the second inductor may be connected to an output terminal of the transformer, a second terminal of the second inductor may be connected to the common node, a first terminal of the impedance element may be connected to the common node, and a second terminal of the impedance element may be connected to the ground.

Provided is a balance-unbalance converter including: a substrate; an unbalanced line; a first balanced line; and a second balanced line on the substrate. The unbalanced line has a first end at which an unbalanced signal is input, and an opened second end. The first balanced line is in parallel with a line portion of the unbalanced line from the first end to a midpoint of the unbalanced line, and has a midpoint-side third end at which a balanced signal is output, and a grounded fourth end. The second balanced line is in parallel with a line portion of the unbalanced line from the second end to the midpoint, and has a midpoint-side fifth end at which the balanced signal is output, and a grounded sixth end. The unbalanced line is bent at the midpoint toward an opposite side of the first and second balanced lines.

Provided is a balance-unbalance converter including: a substrate; an unbalanced line; a first balanced line; and a second balanced line on the substrate. The unbalanced line has a first end at which an unbalanced signal is input, and an opened second end. The first balanced line is in parallel with a line portion of the unbalanced line from the first end to a midpoint of the unbalanced line, and has a midpoint-side third end at which a balanced signal is output, and a grounded fourth end. The second balanced line is in parallel with a line portion of the unbalanced line from the second end to the midpoint, and has a midpoint-side fifth end at which the balanced signal is output, and a grounded sixth end. The unbalanced line is bent at the midpoint toward an opposite side of the first and second balanced lines.

Embodiments provide an amplification circuit, an apparatus for amplifying, a low noise amplifier, a radio receiver, a mobile terminal, a base station, and a method for amplifying. An amplification circuit (10) for amplifying a radio signal comprises a first amplification stage (12) configured to amplify an input signal, V.sub.in(t), to obtain an intermediate signal. The amplification circuit (10) further comprises a cascoding circuit (14) configured to amplify the intermediate signal to obtain a first output signal V.sub.outn(t). The amplification circuit (10) further comprises a second amplification stage (16) configured to amplify the intermediate signal to obtain a second output signal, V.sub.outp(t).