The open-drain type output buffer includes a first driver and at east one of (1) at least one secondary driver and (2) at least one tertiary driver. The first driver selectively pulls an output node towards a low voltage based on input data. The secondary and tertiary drivers have first and second states....http://www.google.de/patents/US6831478?utm_source=gb-gplus-sharePatent US6831478 - Open drain type output buffer
