Patent ID: 7532075

Claim:
A bias circuit connected to an alternating-current circuit, comprising: a first reactance means one end of which is connected to said alternating-current circuit; a capacitive means one end of which is grounded; a direct-current circuit part capable of supplying a direct-current voltage; one or more second reactance means; and a reactance providing means capable of providing a reactance; wherein each of said second reactance means is cascade-connected between the other end of said first reactance means and the other end of said capacitive means; said direct-current circuit part is connected to a connection point (hereinafter referred to as connection point R) between said capacitive means and said second reactance means which is connected to said capacitive means; said connection point R is grounded in terms of alternating current; and said reactance providing means is capable of providing a reactance to an open position (hereinafter referred to as the open position) from which an impedance as viewed toward said capacitive means is sufficiently large between the other end of said first reactance means and the other end of said capacitive means in accordance with an alternating-current frequency (hereinafter referred to as the alternating-current frequency) of an alternating-current signal passing through said alternating-current circuit so that an impedance as viewed from a bias connection point (hereinafter referred to as the bias point) between said alternating-current circuit and said first reactance means is sufficiently large.