Message ID: 2305
Entry time: Wed Feb 6 19:13:06 2019
In reply to: 2304
Reply to this: 2306

Author:

anchal

Type:

Summary

Category:

FSS

Subject:

Complete model of TTFSS box with TF and crossover analysis

I added some more graphs to our FSS analysis.

I modeled AD602 variable gain amplifier with a circuit similar to how it actually works internally. The resultant circuit now has a right input resistance of 100 Ohm and capacitance of 2 pF. It is slightly noisier than AD602.

I calculated the total suppression function and suppressed laser frequency noise.

I did a parametric analysis by varying the PZT gain and obtained a range of cross over frequencies and phase margin we can attain.

Everything looked awesome so far, but the real problem is EOM railing.

So I calculated that if the said suppression is achieved, what is the actuation signal that is sent to EOM.

The last plot is the spectral density of this actuation signal. Since only, we clearly are going to rail the EOM and the said suppression will never actually happen.

We need to shift actuation region of EOM to even higher frequencies so that it doesn't rail. But at the same time, we need to keep the crossover frequency and phase margin of crossover decent. And to top it off, we need to do all this making sure we get at least suppression at 100 Hz.

So from here, I guess we need to work on shifting the poles and zeros and tune in the gain values right to get point.

I'm not 100% sure about this analysis, please let me know if I am doing something wrong here. The latest notebook and pdf are on git.

Quote:

I'm attaching the first results of the transfer function from liso model of complete TTFSS box. I've also attached the jupyter notebook with some important formulas used.