Bias current generating circuit

The invention provides a bias current generating circuit which comprises a reference voltage end, a switching circuit, a self-bias current circuit and a current output circuit, wherein the reference voltage end supplies reference voltage to the switching circuit and the self-bias current circuit; the self-bias current circuit forms first association current according to the reference voltage, andthe first association current is supplied to the switching circuit; the switching circuit comprises an amplifier component, starting of the amplifier component is controlled by the first association current, and the amplifier component generates control current according to the reference voltage, and the control current is supplied to the self-bias current circuit and the current output circuit; the self-bias current circuit generates second association current according to the control current, and operation of the amplifier component is controlled by the second association current after beingstarted; the current outp