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Frequency Response damping

Question asked by jaz on Nov 14, 2011
Latest reply on Nov 17, 2011 by Dr_joel

I have designed PCB Traces with a Tee connection. Port one input is for AC signal input (with DC block) and another is for DC signal input (with inductor). Both AC and DC signal combines and enters my DUT. Similar concept as in Bias tee. However, the frequency response is damping. I do not get smooth/flat response as shown in the attached file. I have simulated the circuit prior of designing and i do not find any damping problem.

May i know what is the possible reasons resonance occur? My assumption is the DC path will not bring effect to my AC signal. DC source is an AC ground (please correct me if wrong) and thus an inductor is placed at the DC source (Vcc).