Power amplifier circuit

A power amplifier circuit comprising:

• an amplifier configured to amplify power of a radio-frequency signal in a transmit frequency band and to output an amplified signal;
• a bias circuit;
• and
• an impedance circuit that is connected between a signal input terminal of the amplifier and a bias-current output terminal of the bias circuit, and that is configured to attenuate signals having frequencies in the transmit frequency band, wherein:
• the impedance circuit comprises:
• a first impedance circuit connected to the signal input terminal, and
• a second impedance circuit connected between the first impedance circuit and the bias-current output terminal,
• the first impedance circuit or the second impedance circuit is an LC parallel resonance circuit comprising an inductive element and a capacitive element disposed in parallel with each other between the signal input terminal and the bias-current output terminal, and
• the other of the first or second impedance circuit is a notch filter circuit comprising first and second T circuits disposed in parallel with each other between the signal input terminal and the bias-current output terminal,
• the first T circuit comprises:
• two resistive elements disposed in series with each other between the signal input terminal and the bias-current output terminal, and
• a capacitive element connected between a reference potential and a node between the two resistive elements, and
• the second T circuit comprises:
• two capacitive elements connected in series with each other and in parallel with the two resistive elements, and
• a resistive element connected between the reference potential and a node between the two capacitive elements.

A power amplifier circuit comprising:

• an amplifier configured to amplify power of a radio-frequency signal in a transmit frequency band, and to output an amplified signal;
• a bias circuit;
• and
• an impedance circuit that is connected between a signal input terminal of the amplifier and a bias-current output terminal of the bias circuit, and that is configured to attenuate signals having frequencies in the transmit frequency band, wherein:
• the impedance circuit comprises:
• first and second inductive elements connected in series with each other between the signal input terminal and the bias-current output terminal,
• a first capacitive element connected in parallel with both the first and second inductive elements, and
• a second capacitive element connected between a reference potential and a node between the first and second inductive elements,
• the first inductive element, the second inductive element, and the first capacitive element form an LC parallel resonance circuit, and
• the first inductive element, the second inductive element, and the second capacitive element form an LC low-pass filter circuit.