Standard schematic of an HDSL2 line driver with current-feedback op amps
<a href="//commons.wikimedia.org/w/index.php?title=User:Retired_electrician&amp;action=edit&amp;redlink=1" class="new" title="User:Retired electrician (page does not exist)">Retired electrician</a>
<span class="int-own-work" lang="en">Own work</span>. The basic schematic is ubiquitous (e.g. <a rel="nofollow" class="external text" href="http://www.linear.com/product/LT1497">here</a>) and patent-free. Anything patentable there has been in use since at least 1960s.