Differential amplifier circuit

A differential amplifier circuit comprising:

• a first amplifier and a second amplifier that output a differential signal in a radio-frequency band;
• a first inductor having a first end connected to an output end of the first amplifier, and a second end;
• a second inductor having a first end connected to an output end of the second amplifier, and a second end,
• the second end of the first inductor and the second end of the second inductor being connected to each other;
• a choke inductor connected to the second end of the first inductor and the second end of the second inductor;
• a first capacitor having a first end connected to the second end of the first inductor and the second end of the second inductor, and a second end connected to a reference potential;
• a first series resonant circuit having a first end connected to the output end of the first amplifier, and a second end connected to the reference potential;
• and
• a second series resonant circuit having a first end connected to the output end of the second amplifier, and a second end connected to the reference potential, wherein
• each of the first series resonant circuit and the second series resonant circuit includes an inductor and a capacitor that are connected in series,
• the first inductor or the second inductor is connected in series with the first capacitor to form a resonant circuit having a first resonant frequency, and each of the first series resonant circuit and the second series resonant circuit has a second resonant frequency, the first resonant frequency and the second resonant frequency being different from each other, and
• the first resonant frequency and the second resonant frequency correspond to second harmonic frequencies of the differential signal.

A differential amplifier circuit comprising:

• a first amplifier and a second amplifier that output a differential signal in a radio-frequency band;
• a first inductor having a first end connected to an output end of the first amplifier, and a second end;
• a second inductor having a first end connected to an output end of the second amplifier, and a second end,
• the second end of the first inductor and the second end of the second inductor being connected to each other;
• a choke inductor connected to the second end of the first inductor and the second end of the second inductor;
• a third inductor disposed in parallel to the first inductor and the second inductor, the third inductor having a first end connected to the output end of the first amplifier, and a second end connected to the output end of the second amplifier;
• a first capacitor having a first end connected to a midpoint of the third inductor, and a second end connected to a reference potential;
• a transformer having a primary winding and a secondary winding that are electromagnetically coupled to each other, the transformer being configured to perform balanced-to-unbalanced conversion, the primary winding of the transformer being used to implement the first inductor and the second inductor;
• and
• a series resonant circuit including one half of the third inductor and the first capacitor.