I started work on a LISO model of the PMC servo - it does not yet agree with reality.
Yesterday, I measured the open loop gain (OLG) of the PMC loop.
It consists of two parts, which are the PMC servo's OLG and the rest, i.e. OLG of photodiode, PMC, PZT actuator.
Knowing each part's OLG is useful for modification.
Since we are going to do most modification on the PMC's servo, we want to know what is its TF.
This is where LISO comes in. I use it to simulate the TF of the PMC servo.
I don't know how to model AD602, because it is not actually an opamp and therefore not in the LISO opamp library.
The datasheet says it has -3db at 35MHz. Thus, for our region of interest, it probably has a flat response. It is just an
adjustable gain amplifier.
I'm not sure how to use LISO to calculate poles and zeros of my model yet. I'm reading the manual.
This simulation will be compared with the measurement.
Once we verify that all the parts behave the way they should, we can think about the modification.
We want to modify the TF because even though we maximize the gain slider, the system is still stable
( no sign of oscillaltion from too much gain.) It means we can still optimize our TF for better stability.
Lastly, knowing the servo's OLG and the whole loop OLG,
we can compute what is the OLG of the rest of the system by simple subtraction.
I hope the quality of this elog entry is improved, however slightly it might be. It has motivation why I do what I do, details, and people who want to reproduce my work should be able to follow it.
Thanks Koji for a useful discussion on how to elog properly.
The attached plot shows modeled transfer function of the PMC Servo card + PZT capacitance.
Components' names in LISO code are taken from the schematic
# Noise sim for pmc servo
# Tara C, 2010_09_17
r R41 49.9 n0 gnd
l L1 20u n0 n1
r R42 470 n1 n2
c C4 82p n2 gnd