Patent ID: 6060907
Filing Date: 2000-05-09
Classification: H03K

Abstract:
An impedance control apparatus for controlling a driver circuit having an output impedance, the driver circuit including a base bit element and a controllable bit element, the controllable bit element being controllable to adjust the output impedance of the driver circuit, the apparatus comprising:a bit element circuit, the bit element circuit including a base bit element and a controllable bit element, the base bit element and the controllable bit element having substantially the same characteristics as the base bit element and the controllable bit element of the driver circuit, the controllable bit element controllable so as to provide an output impedance substantially corresponding to the output impedance of the driver circuit;a comparator coupled to the bit element circuit and to a resistance substantially corresponding to an impedance of a transmission line to which the driver circuit is coupled, the comparator comparing the output voltage of the bit element circuit to the voltage of the resistance and providing an output signal, the output signal indicating whether the output voltage of the bit element circuit or the voltage of the resistance is higher; anda shift circuit coupled to the comparator and to the controllable bit element, the shift circuit providing a bit element control signal based upon the output signal, the bit element control signal controlling whether the controllable bit element is on or off.