AD8131 and AD8138 phase tracking info

Document created by analog-archivist Employee on Feb 23, 2016
Version 1Show Document
  • View in full screen mode

information regarding relative phase tracking for the AD8138 vs the AD8131


The diff amps have a propagation delay, which adds a slight negative tilt to
their open-loop phase responses.  To put this in perspective, one nanosecond is
90 degrees at 250 MHz.  If the propagation delay were one nanosecond, it would
therefore add an additional negative 90 degree shift to the open-loop phase
response, which would make the part unstable.  It’s safe to say that the
propagation delay is well under one nanosecond, and the part-to-part variations
are correspondingly smaller.  We don’t generally specify propagation delay on
the amplifier data sheets since it is usually insignificant, and is contained
(usually imperceptively) in the open-loop phase response.

For more info see AD8131 and AD8138 phase tracking info (SR#: 1238742)