Current source and digital to analog converter

A current source, comprising:

• a current output circuit, comprising:
• a first PMOS transistor;
• and
• a second PMOS transistor;
• an impedance gain circuit, configured to increase output impedance of the current output circuit, the impedance gain circuit comprising:
• a first end;
• a second end;
• a third end which is connected to a supply voltage;
• a fourth end which is connected to a ground;
• a third PMOS transistor;
• a fourth PMOS transistor;
• several PMOS transistors which are connected in series;
• and
• a pull-up electric potential module;
• wherein a source electrode of the first PMOS transistor is connected to the supply voltage, a drain electrode of the first PMOS transistor is connected to a source electrode of the second PMOS transistor and the first end of the impedance gain circuit, and a gate electrode of the first PMOS transistor is controlled by a first bias voltage;
• wherein a gate electrode of the second PMOS transistor is connected to the second end of the impedance gain circuit, and a drain electrode of the second PMOS transistor serves as an output end of the current source;
• wherein a gate electrode of the third PMOS transistor is connected to the first end of the impedance gain circuit, a source electrode of the third PMOS transistor is connected to the third end of the impedance gain circuit, and a drain electrode of the third PMOS transistor is connected to a source electrode of the fourth PMOS transistor by using the several PMOS transistors which are connected in series;
• wherein a drain electrode of the fourth PMOS transistor is connected to the second end of the impedance gain circuit, and a gate electrode of the fourth PMOS transistor is controlled by a second bias voltage;
• and
• wherein one end of the pull-up electric potential module is connected to the second end of the impedance gain circuit, and another end of the pull-up electric potential module is connected to the fourth end of the impedance gain circuit.