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Message ID: 1775     Entry time: Wed Jul 22 11:08:36 2009
Author: Stephanie 
Type: Update 
Category: General 
Subject: Multiply Resonant EOM Update 

I have built a version of the circuit with flying components; the completed circuit is shown in the attached picture. I built the circuit in segments and measured the transfer function after each segment to see whether it matched the LTSpice simulation after each step. The segments are shown in the circuit diagram.

After building the first segment, the measured transfer function looked pretty much the same as the simulated transfer function; it appears shifted in the attached plot, but this is because I didn't do a careful job of tuning at this point, and I'm relatively sure that I could have tuned it to match the simulation. After adding the second segment of the circuit, the measured and simulated transfer functions were similar in shape, but I was unable to increase the frequency of the peaks (through tuning) any more than what is shown in the plot (I could move the peaks so that their frequency was lower, but they are shown as high as they will go). When I added the final segment to complete the circuit, the measured and simulated transfer functions no longer had the same shape; two of the peaks were very close together and I was barely able to differentiate one from the other.

In order to understand what was happening, I tried making modifications to the LTSpice model to recreate the transfer function that was measured. I was able to create a transfer function that closely resembles the measured transfer function in both the circuit as of the 2nd segment and the completed circuit by adding extra inductance and capacitance as shown in red in the circuit diagram. The transfer functions simulated with these parasitic components are shown in red in both plots. While I was able to recreate the response of the circuit, the inductance and capacitance needed to do this were much larger than I would expect to occur naturally within the circuit (2.2uH, 12 pF). I'm not sure what's going on with this.

Attachment 1: BuiltCkt_Picture.png  450 kB  | Hide | Hide all
Attachment 2: BuiltCkt2_Final.png  36 kB  | Hide | Hide all
Attachment 3: 1stSegment.png  13 kB  | Hide | Hide all
Attachment 4: 2ndSegment_ExtraL.png  13 kB  | Hide | Hide all
Attachment 5: Complete_ExtraL.png  14 kB  | Hide | Hide all
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