Patent ID: 8854142

Claim:
A bias circuit comprising: a bias setting unit setting a bias power voltage level by switching reference power having a pre-set voltage level determined according to a pre-set power mode; and a bias supply unit including a switching element performing switching according to the setting of the bias setting unit and supplying bias power having a voltage level determined according to a switching operation of the switching element, wherein the switching element is a supply transistor, the bias setting unit includes: a first transistor switched on or off according to the pre-set power mode, wherein the first transistor is switched on when the pre-set power mode is a high power mode, and is switched off when the pre-set power mode is a low power mode, a second transistor switched on as the first transistor is switched on and causing a base voltage of the supply transistor to be increased, wherein the second transistor is switched on when the pre-set power mode is a high power mode, and is switched off when the pre-set power mode is a low power mode, a third transistor switched on as the first transistor is switched off and causing the base voltage of the supply transistor to be lowered, wherein the third transistor is switched on when the pre-set power mode is a low power mode, and is switched off when the pre-set power mode is a high power mode, and a capacitor for charging the reference power, wherein the second transistor has a base connected to the capacitor to receive the power charged in the capacitor as the third transistor is switched on or off, wherein the second transistor has a collector receiving driving power having a pre-set voltage level, and wherein the supply transistor has a collector receiving the driving power, a base receiving the power charged in the capacitor, and an emitter supplying the bias power through a resistor.