Semiconductor circuit, d/a converter, mixer circuit, radio communication device, method for adjusting threshold voltage, and method for determining quality of transistor

A method for adjusting a threshold voltage of a transistor having a charge storage film between a region of a substrate made of a semiconductor between two diffusion layers formed in the substrate and a gate electrode, the method comprising:

• detecting a gate voltage, a drain voltage and a substrate voltage;
• determining whether or not a threshold voltage changing with charge stored in the charge storage film has reached a target value and whether or not a total amount of charge flowing through the substrate has reached an upper limit on a basis of the gate voltage, the drain current and the substrate current that are detected;
• and
• controlling the substrate current to flow so that charge is stored in the charge storage film until either the target value or the upper limit is determined to be reached.

A method for determining a quality of a transistor having a charge storage film between a region of a substrate made of a semiconductor between two diffusion layers formed in the substrate and a gate electrode, the method comprising:

• detecting a gate voltage, a drain voltage and a substrate voltage;
• determining whether or not a threshold voltage changing with charge stored in the charge storage film has reached a target value and whether or not a total amount of charge flowing through the substrate has reached an upper limit on a basis of the gate voltage, the drain current and the substrate current that are detected;
• controlling the substrate current to flow so that charge is stored in the charge storage film until either the target value or the upper limit is determined to be reached;
• and
• determining as good quality when the target value is reached before the upper limit is reached but determining as bad quality when the upper limit is reached before the target value is reached.