System and method of automatic power control system and bias current control circuit

An automatic power-control system, comprising:

• an oscillator circuit, outputting a voltage signal;
• and
• a bias-current-control circuit, including:
• a transconductance circuit, connecting a node and detecting the voltage signal to generate a first current;
• a constant-current source, connecting the node and generating a tail current;
• and
• a current-mirror circuit, including a reference current terminal coupled to the node and a bias current terminal connected to a current input terminal of the oscillator circuit;
• wherein a second current which flows through the reference current terminal is determined by a current difference between the tail current and the first current;
• wherein a bias current which flows through the bias current terminal is generated based on the second current;
• wherein the second current and the bias current are in a predetermined ratio.

An automatic power-control method, comprising:

• generating, by a transconductance circuit, a first current based on a voltage signal output by an oscillator circuit;
• generating, by a current-mirror circuit, a bias current according to a current difference between the first current and a tail current of a constant-current source;
• and
• providing the bias current to the oscillator circuit;
• wherein the second current and the bias current are in a predetermined ratio.