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Entry  Mon Oct 21 12:25:46 2019, gautam, Update, ALS, DFD electronics checkout ALSnoiseAnomaly.pdfDFDcalib.pdfspectra.pdfPTgains.pdf
    Reply  Tue Oct 22 15:32:15 2019, gautam, Update, ALS, EX uPDH electronics checkout uPDH_X_OLTFs.pdf
       Reply  Wed Oct 23 10:23:26 2019, rana, Update, ALS, EX uPDH electronics checkout 
          Reply  Wed Oct 23 11:11:01 2019, gautam, Update, ALS, EX uPDH electronics checkout 
    Reply  Fri Oct 25 01:04:49 2019, gautam, Update, ALS, ALS electronics chain was saturating 
       Reply  Mon Oct 28 23:20:11 2019, gautam, Update, ALS, ALS power budget 
Message ID: 14995     Entry time: Mon Oct 28 23:20:11 2019     In reply to: 14993
Author: gautam 
Type: Update 
Category: ALS 
Subject: ALS power budget 

 

IR ALS power budget
Photodiode PSL VDC [V] PSL IDC [uA] AUX VDC [V] AUX IDC [uA] IRF [mA pk] PRF [dBm]
PSL+EX 3 300 2.5 250 ~600  ~3
PSL+EY 3 300 0.6 60 ~270 ~ -3

In calculating the above numbers, I assumed a DC transimpedance of 10 khhms and an RF Transimpedance of ~800 V/A.

[Elog14480]: per these calculations, with the NewFocus 1611 PDs, we cannot achieve shot noise limited sensing for any power below the rated maximum for linear operation (i.e. 1mW). Moreover, the noise figure of the RF amplifier we use to amplify the sensed beat note before driving the delay-line frequency discriminator is unlikely to be the limiting noise source in the current configuration. Rana suggested that we get two Gain Blocks. These can handle input powers up to ~10dBm while still giving us plenty of power to drive the delay line. This way, we can (i) not compromise on the sacred optical gain, (ii) be well below the 1dB compression point (i.e. avoid nonlinear noise effects) and (iii) achieve a better frequency discriminant

Temporary fix: While the gain blocks arrive, I inserted a 10dB (3dB) attenuator between the PSL+EX (PSL+EY) photodiode RF output and the ZHL-3A amplifiers. This way, we are well below the 1dB compression point of said RF amplifiers, and also below the 1dB compression point of the on-board Teledyne AP1053 amplifiers on the demodulator boards we use.

Nest steps: Rana is getting in touch with Rich Abbott to find out if there is any data available on the noise performance of the post-mixer IF amplifier stage in the 0.1 -30 Hz range, where the voltage and current noise of the AD829 OpAmps could be limiting the DFD performance. But in the meantime, the ALS noise seems good again, and there is no evidence of the sort of CARM/DARM coupling that motivated this investigation in the first place. Managed to execute several IR-->ALS transitions tonight in the PRFPMI locking efforts (next elog).

No new Teledyne AP1053s were harmed in this process - I'll send the 5 units back to Rich tomorrow.

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