Patent ID: 7339417

Claim:
A current source circuit, comprising a startup circuit and a bias circuit being connected to each other between a power supply and ground, the startup circuit operating at power-on, the bias circuit starting to pass current when the startup circuit operates, said startup circuit, comprising: a second PMOS transistor having a source connected to the power supply, a gate connected to an isolating voltage node from the bias circuit, and a drain connected to a shift voltage node; a fourth capacitor connected between the shift voltage node and the ground; a third PMOS transistor having a source connected to the power supply and a gate connected to a control voltage node; a fourth PMOS transistor having a source connected to the power supply, a gate connected to a drain of the third PMOS transistor, and a drain connected to the gate of the third PMOS transistor; an eighth NMOS transistor having a drain connected to the gate of the fourth PMOS transistor, a gate connected to the shift voltage node, and a source connected to the ground; a fifth PMOS transistor having a source connected to the control voltage node, a gate connected to the shift voltage node, and a drain connected to the ground; and a sixth PMOS transistor having a source connected to the power supply, a gate connected to the control voltage node, and a drain connected to a starting voltage node, said bias circuit having a current mirror circuit formed therein, starting passing current of the current mirror circuit in response to a trigger from the startup circuit to the starting voltage node, and outputting a bias voltage to the isolating voltage node after passing the current through the current mirror circuit.