Suspension Actuator noise:

There are 3 main sources of electronics noise which come in through the coil driver:

1. Voltage noise of the coil driver.
   1. The input referred noise is ~5 nV/rHz, so not a big issue.
   2. The Johnson noise of the output resistor which is in series with the coil is sqrt(4*k*T*R) ~ 3 nV/rHz. We probably want to increase this resistor from 200 to 1000 Ohms once Gautam convinces us that we don't need that range for lock acquisition.
2. Voltage noise of the dewhitening board.
   1. In order to reduce DAC noise, we have a "dewhitening" filter which provides some low passing. There is an "antiDW" filter in the digital part which is the inverse of this, so that when they are both turned on, the result is that the main signal path has a flat transfer function, but the DAC noise gets attenuated.
   2. In particular, ours have 2 second order filters (each with 2 poles at 15 Hz and 2 zeros at 100 Hz).
   3. We also have a passive pole:zero network at the output which has z=130, 530 Hz and p = 14, 3185 Hz.
   4. The dewhitening board has an overall gain of 3 at DC to account for our old DACs having a range of +/-5 V and our coil drivers having +/- 15 V power supplies. We should get rid of this gain of 3.
   5. The dewhitening board (and probably the coil driver) use thick film resistors and so their noise is much worse than expected at low frequencies.
3. DAC voltage noise. 
   1. The General Standards 16-bit DACs have a noise of ~5 uV/rHz.
4. the satellite box is passive and not a significant source of noise; its just a flaky construction and so its problematic.