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Entry  Thu Aug 2 15:01:21 2018, awade, DailyProgress, WOPO, Building a SN limited detector for WOPO experiment 6x
    Reply  Mon Aug 6 17:30:53 2018, awade, DailyProgress, WOPO, Too much RIN, making a balanced detector plot20180803_Single6p8kTIADect_NoiseSpectrum.pdfSch20180806_SumWtTrim_IMG_3631.JPG
       Reply  Thu Aug 9 16:51:43 2018, awade, DailyProgress, WOPO, Testing balanced detector 
          Reply  Mon Aug 20 12:11:45 2018, awade, DailyProgress, WOPO, Testing (freespace) balanced detector 18-08-17_22-59-08_3649.jpg
             Reply  Mon Aug 20 22:09:27 2018, awade, DailyProgress, WOPO, PZT broken no slow phase modulation on LO 
                Reply  Wed Aug 22 00:42:42 2018, awade, DailyProgress, WOPO, New PZT mounted mirror 18-08-22_22-28-27_3673.jpg18-08-22_22-32-51_3678.jpg18-08-22_22-34-17_3680.jpg18-08-23_12-02-38_3684.jpg18-08-23_12-02-48_3686.jpg
                   Reply  Thu Aug 23 12:49:17 2018, awade, DailyProgress, WOPO, New PZT mounted mirror mounted IMG_3690_ThePriestAndTheBeast.JPG
       Reply  Mon Aug 13 01:48:48 2018, rana, DailyProgress, WOPO, SR560 battery as a voltage supply 
          Reply  Wed Aug 15 09:57:56 2018, awade, DailyProgress, WOPO, SR560 battery as a voltage supply 
       Reply  Mon Aug 13 01:53:21 2018, rana, DailyProgress, WOPO, zero-span spec OR RF bandpass 
          Reply  Mon Aug 13 15:43:55 2018, Chris, DailyProgress, WOPO, zero-span spec OR RF bandpass 
          Reply  Mon Aug 20 12:08:17 2018, awade, DailyProgress, WOPO, zero-span spec OR RF bandpass 
    Reply  Wed Mar 27 20:37:38 2019, awade, DailyProgress, WOPO, Measuring TF Homodyne Photo Detector for WOPO experiment TFUnitAandB_BeforeMatchingOutImp.pdfTFUnitAandB_FixingDetectorAImp.pdfWOPO_HD_TranImpGain_UnitAandBandLISO.pdf
       Reply  Fri Mar 29 16:00:21 2019, awade, DailyProgress, WOPO, Remeasuring TF Homodyne Photo Detector B after switching out foil cap 
          Reply  Wed Apr 10 13:10:45 2019, awade, DailyProgress, WOPO, Rebuild of WOPO homodyne detectors using AD829 BasicSchematic_TranImpPD_AD829.pdf19-04-02_19-42-47_5777.jpg19-04-04_12-39-15_5797.jpgWOPO_HDPD_AD829_2kohmTranImpGain_UnitAandBandLISO.pdf20190405_TFHDPDs_AD829Design_LargeBoard.zip
Message ID: 2318     Entry time: Fri Mar 29 16:00:21 2019     In reply to: 2316     Reply to this: 2324
Author: awade 
Type: DailyProgress 
Category: WOPO 
Subject: Remeasuring TF Homodyne Photo Detector B after switching out foil cap 

This set of measurments turned out to be bad. The OP27 (±15V supplies) with 50 Ω series at the output + 50 Ω load impedance seemed to be saturated.

The rest of this post is a stream of conciseness.

As noted in previous post (ATF:2316) the PD unit B in the homodyne had a slightly reduced HF response, possibly due to the use of a foil cap in the PD bias supply low pass.  I removed this and resmeasured.

Unit B TF: measured NF1611 DC voltage of  312 mV (@ 50Ω impedance), PD DC output voltage was - 566 mV (@ 50 Ω impedance).  Here the photodetector has transresistance is 6.8 kΩ. The NF1611 detectors have a DC path gain of 10 kΩ and an AC path gain of 700 Ω. From this the R_PC is xxx.  Here I ignore the overall phase (at ~1 MHz as the pi phase shift length is 150 m, so negligible).  This was a bad measurment, something was up with the circuit saturating way too low.  

Changed 100 Ω series on output to 50 Ω to make it more strait forward to understand how it works with 50 Ω load. 

Unit A TF: measured NF1611 DC voltage of  658 mV (@ 50Ω impedance), PD DC output voltage was 1.42 mV (@ 50 Ω impedance).  Here the photodetector has transresistance of 6.8 kΩ. The NF1611 detectors have a DC path gain of 10 kΩ and an AC path gain of 700 Ω. From this the R_PC is 0.3151.  Here I ignore the overall phase (at ~1 MHz as the pi phase shift length is 150 m, so negligible).  This measurment could have be saturating the current output of the OP27, likely that numbers here are not right.

After examining the output of detector B it became apparent that the output was saturated for powers of more than ~20 mA laser diode drive. 

Unit B TF: measured NF1611 DC voltage of  312 mV (@ 50Ω impedance), PD DC output voltage was -566 mV (@ 50 Ω impedance).  Here the photodetector has transresistance is 6.8 kΩ. The NF1611 detectors have a DC path gain of 10 kΩ and an AC path gain of 700 Ω. From this the R_PC is -0.3748.  Here I ignore the overall phase (at ~1 MHz as the pi phase shift length is 150 m, so negligible).   100 Ω  (50Ω + 50 Ω) loading is too low, OP27 open loop gain and voltage swing range slew starts to sag below 150Ω loading.  These results are bogus.

This time I measured with 50 Ω on the oscilloscope for apples-to-apples comparison with what the Aglient 4395A was seeing.  Turns out I think I was saturating the photodetector current wise in the first round of measurments. All of the above is probably not right and should be disregarded.  Also, later I switched to a AD829 as the op amp of choice so the above is not much use for characterizing the detector performance anymore.  The OP27 isn't really spec'ed to operate with loads this low and only has its full band with for output loads of >2 kΩ.  

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