Damping Resistor(s) for MCLK Distribution

Discussion created by KJBob on Jan 23, 2014
Latest reply on Oct 1, 2015 by DaveThib

     The picture below shows a ADAU1401 eval board sending TDM audio to a ADAU1701 on a re-purposed prototype board.  Four twisted pairs run the MCLK, BCLK, LRCLK, and TDM data between the boards.


     The received sound was erratic until I spliced a 150 ohm resistor into the yellow MCLK wire near its source end.  The 1401's MCLK output has a lo-Z buffer which rings with the unterminated wire, as shown below, left.  It looks much better with the resistor at right:


     Thus it's a good idea to damp the MCLK signal between chips, especially when pcb traces or wires are long,