Oscillation issue on THS4271


Posted on Feb 6, 2014

I got oscillation issueon THS4271. The circuit schematic is as attached. The input is differential sine wave on positive and negative terminals with 10k differential resistor. The output oscillates at 300Mhz or mixed frequency as attached. Once turn off the sine wave SG, the output continue to oscillate. If changing THS3091 with appropriate recomme


Oscillation issue on THS4271
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nded Rf, the circuit is clean without oscillation. Could someone tell me what`s going on with THS4271 Are you using +/-15V (30V total) supplies as your schematic appears to indicate The THS4271 is only rated for up to 16. 5V total supply, so you are exceeding this limit. Does the circuit oscillate if you reduce the supplies to +/-5V or +/-7. 5V If the circuit still oscillates, try isolating the oscillation. Check if the outputs of U1 and U3 show an oscillation. Do you have all planes/fills cut out below the input/output pins, or just the layer immediately below the top layer The best practice is to remove all copper on all layers below the input/output pins Would it be possible to cut the trace from the U3 output to R6 to isolate U3 completely Perhaps the parasitic capacitance of the trace to R6 is causing U3 to oscillate. I suggest cutting the top trace as I`ve shown in the image below. Cut and remove the trace to form a space for a resistor to be soldered across points 1 and 2 (red boxes). Thanks for the response! I did remove the ground plane under the signal between inverting and output node but not for power and other planes. I am afraid there`s some other issues when I cut off the power planes. I also follow your instruction to probe output through 50 ohm resistance but it doesn`t work. I increase R3 and R8 FROM 249Kto 499K. It seems OK w/o oscillation. All content and materials on this site are provided "as is". TI...




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