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Oscillation with AD8137

Question asked by UweBonnes on Feb 27, 2014
Latest reply on Mar 3, 2014 by harryh


I have an AD8085 driving a AD8137 with gain 10 with a roll-off at about 1 MHz:


The board is FR4, two layer with 1.6 mm thickness. Bottom layer is mostly ground with lots of ground vias. Running the circuit for some time, an oscillation with about 20 mV and about 100 MHz appears, observed with a probe on DO+. Touching e.g. DO- with an isolated  screwdriver or switching off and on again the supply removes the oscillation , to appear again at random. Copper from the ground plane below the summing nodes is not removed, but stray capacitance should be small, as overall area of summing nodes is small, FR4 thickness high and C41/C42 form are the "small capacitors across the feedback resistors" as in the datasheet "Layout considerations".

Any hints for me?