[Kenta, YamaT]

This is yesterday's work.

Add 16kto2k filter for AS34 at PD filterbank
When we checked all RF PDs to trace the signal path for the future calibration work, we found POP90 has "16kto2k" filter at FM9 of PD filterbank but AS34 doesn't. These two PDs are used for power normalization in LSC and the reference signal of ADS. Sending AS34 without AA filter to 2kHz ADS model makes aliasing noise on the error signal of ADS, so we added same "16kto2k" filter at FM9 of AS34 PD filterbank. According to the comparison plot of AS34 signal with and without AA on k1ascads, AA filter makes ~2 times improvement of noise floor around 30Hz (near dither frequency). Orange curve in Fig.1 represents original AS34_I on k1lsc. Green and blue curves represents AS34_I on k1ascads with and without AA filter, respectively. Note that, blue curve (without AA) is simulated one with original signal and offfiline signal processing (simulated filterbank, phase rotation, power normalize and decimation) because there is no proper DQ channel on k1ascads for checking aliasing noise and I forgot to take a spectrum data befor applying AA.

Add LP1 before power normalization of error signals
We also noticed MICH and SRCL error signal were divided by raw (non-lowpassed) AS34_I as the power normalization. (PRCL error signal is divided by low-passed POP90_I.) Since this implementation seemed to simply introduce noise derived from high-frequency components, we also added "LP1" filter (same as POW_NORM_POP90_I_FILT) at FM1 of POW_NORM_AS34_I_FILT.