Patent ID: 6184730
Filing Date: 2001-02-06
Classification: H03K

Abstract:
A high-drive output buffer with active termination comprising:an output pad for connecting to an external output load;a pullup driver transistor, coupled to strongly drive the output pad to a higher voltage during a rising transition of the output pad, the pullup driver transistor being controlled by a pullup gate;a pulldown driver transistor, coupled to strongly drive the output pad to a lower voltage during a falling transition of the output pad, the pulldown driver transistor being controlled by a pulldown gate;a sensor, coupled to the output pad, for detecting when the output pad has been driven to a threshold voltage, the sensor disabling the pullup driver transistor near an end of the rising transition, the sensor disabling the pulldown driver transistor near an end of the falling transition;a pullup transmission gate, coupled to the output pad, for providing a terminating impedance to the output pad after the end of the rising transition after sensor has disabled the pullup driver transistor, the pullup transmission gate also for weakly driving the output pad to a higher voltage during the rising transition; anda pulldown transmission gate, coupled to the output pad, for providing a terminating impedance to the output pad after the end of the falling transition after sensor has disabled the pulldown driver transistor, the pulldown transmission gate also for weakly driving the output pad to a lower voltage during the falling transition,whereby the output pad is terminated by the pullup transmission gate after the rising transition, but terminated by the pulldown transmission gate after the falling transition.