Patent ID: 7286004

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 first PMOS transistor having a source connected to the power supply and having a gate and a drain connected to a shift voltage node; a second capacitor connected between the shift voltage node and the ground; a third capacitor having one end connected to the power supply; a fourth NMOS transistor having a drain connected to the other end of the third capacitor, a gate connected to the shift voltage node, and a source connected to a control voltage node; a fifth NMOS transistor having a drain connected to the control voltage node, a gate connected to an isolating voltage node for outputting a bias voltage from the bias circuit, and a source connected to the ground; and a sixth NMOS transistor having a drain connected to a starting voltage node, a gate connected to the control voltage node, and a source connected to the ground, 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 the bias voltage to the isolating voltage node after passing the current through the current mirror circuit.