Summary
Our current quad distribution scheme for DARM should be compatible with the new low-noise ESD driver. Most of our rms drive to the ESD happens below 3 Hz, so the extra compensation required for the new 2 Hz / 50 Hz pole/zero pair shouldn't cost us anything.
Details
In the ETMY ESD drive we currently have passive filters installed (D1500113), with a pole at 1.6 Hz and a zero at 53 Hz. We digitally compensate for these in the L2L drivealign filter for L3.
If we remove these passive filters and install the new low-voltage driver (D1500016), we will instead have two poles at 2.2 Hz and two zeros at 50 Hz, and we'll compensate these digitally in the same way. So we will effectively have an extra pole around 2 Hz and an extra zero around 50 Hz, compared to what we have now.
I've attached a set of spectra of the ETMY ESD drive in full lock. The blue is our current drive. The red is my projection of the drive we would have if we install the new driver and compensate accordingly. It seems that most of the rms in the drive comes from 3 Hz and below, so the total rms (about 3×103 ct) won't change much when we change the digital compensation.
This is wrong. I forgot that the new driver has less dc gain for the quadrants than the Strathclyde driver, so of course we will have to push more DAC counts out at all frequencies.