US Patent 7095246 Variable impedance output buffer

An output buffer circuit (10, 40, 50) includes an output driver transistor (12), a predriver circuit (14, 54), and a bias generator (16, 54). The predriver circuit (14, 54) has an input terminal for receiving an input signal (IN), a first terminal coupled to a power supply voltage terminal, a second terminal, and an output terminal coupled to the control electrode of the transistor (12). The bias generator (16, 54) is coupled to the second terminal of the predriver circuit (14, 54), and provides a bias voltage (VG) to the second terminal of the predriver circuit (14, 54) for controlling the gate voltage of the output driver transistor (12).