Bias circuit

A bias circuit, comprising:

• a bias supply terminal configured to supply a direct-current voltage and/or a direct current to an active device;
• a parallel capacitor connected at one end thereof to the bias supply terminal and grounded at the other end thereof;
• and
• a parallel circuit connected in parallel with the parallel capacitor and connected at one end thereof to the bias supply terminal,
• wherein letting N denote a predetermined integer equal to or greater than 2, and m denote each integer equal to or greater than 1 and equal to or smaller than N−1,
• the parallel circuit comprises:
• a direct-current power supply connection terminal connected to a direct-current circuit part including a direct-current power supply;
• N series inductors connected in series with each other between the bias supply terminal and the direct-current power supply connection terminal;
• and
• N−1 series resonators,
• an m-th one of the N−1 series resonators from the bias supply terminal side includes an m-th resonant capacitor and an m-th resonant inductor and is connected at one end thereof to a connecting point between an m-th and (m+1)-th ones of the N series inductors from the bias supply terminal side and grounded at the other end thereof, wherein
• letting n denote an integer equal to or greater than 2 and equal to or smaller than N+1 and letting a resonance frequency of the (n−1)-th series resonator be referred to as an (n−1)-th frequency fn−1,
• for n=2, an inductance of a first one of the N series inductors and a capacitance of the parallel capacitor are set so that a combined admittance of the parallel capacitor and the first one of the N series inductors is zero at a first frequency f1;
• for n equal to or greater than 3 and equal to or smaller than N+1, an inductance of each of the resonant inductors and a capacitance of each of the resonant capacitors are set so that a combined admittance of the parallel capacitor, the first to the (n−1)-th series inductors and the first to an (n−2)-th series resonators is zero at the (n−1)-th frequency fn−1.