Patent ID: 7397309
Filing Date: 2008-07-08
Classification: H03F

Abstract:
1. A bias circuit for an amplifier for providing a bias voltage to the amplifier comprising a ground, a first transistor, a second transistor, a first resistive load, and a first supply voltage, which are connected in series in this order, wherein in the amplifier, a first bias voltage is provided to a gate electrode or a base of the first transistor, and a second bias voltage is provided to a gate electrode or a base of the second transistor, said bias circuit comprising: a third transistor having a gate electrode and a drain electrode, or a collector and a base, diode-connected, the drain electrode or collector of said third transistor providing the first bias voltage of the amplifier; and a fourth transistor, a fifth transistor and a second resistive load which are connected in series in this order, said first resistive load being connected to a second supply voltage, said fourth transistor having a gate electrode or a base connected to a drain electrode or a collector of said third transistor, said fifth transistor having a gate electrode and a drain electrode, or a base and a collector, diode-connected, the drain electrode or collector of said fifth transistor providing the second bias voltage; wherein, with said second resistive load having resistance Rb and conducting a direct current Ib therethrough, and the first resistive load having resistance Ra and conducting a direct current therethrough equal to k×Ib, the resistance Ra is substantially equal to or more than Rb×(1/k), wherein k is a constant.