Here we’re taking advantage of the fact that the LMH6739, which is a triple Programmable Gain Buffer, or PGB, has individual shutdown for each of its three outputs in order to construct a simple high speed 3:1 MUX. Note that the outputs are all tied together and the selected channel is decoded using a binary code decimal to decimal decoder, BCD to decimal decoder, which would then ensure only one of the three DISABLE_BAR pins is high at any one time. DISABLE_BAR means you’re in disable when you pull that pin low. The same thing can also be done by using the LMH6738 which would require the six gain setting resistors to be placed on the board, instead of being fabricated on the die itself as is the case for the LMH6739 shown here.