Transmitter, integrated circuit and method for calibrating output impedance

An integrated circuit (IC), comprising:

• a calibration circuit, comprising:
• a ring oscillator configured to provide a first clock signal;
• a frequency divider configured to divide the first clock signal to provide a second clock signal;
• and
• a time to digital converter configured to provide a control signal according to the second clock signal and a reference clock;
• and
• a driver coupled to a pad, and comprising:
• a plurality of first transistors;
• and
• a plurality of second transistors,
• wherein the number of the first transistors coupled in parallel between a power supply line and the pad and the number of the second transistors coupled in parallel between a ground and the pad are dynamically controlled according to the control signal.

A method for calibrating an output impedance of a driver, comprising:

• generating a clock signal by a ring oscillator;
• dividing the clock signal by an integer value, wherein the integer value is a multiple of 2;
• converting a time interval of the divided clock signal to a digital code according to a reference clock;
• and
• controlling the number of transistors coupled in parallel in the driver coupled to a pad according to the digital code, so as to keep the output impedance.