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Entry  Tue Nov 5 16:47:19 2013, rana, Frogs, LSC, illegal power supply about to expire 20131023_222351.jpg
    Reply  Tue Nov 5 17:12:48 2013, Jenne, Frogs, LSC, illegal power supply about to expire 
    Reply  Wed Nov 6 14:47:41 2013, Steve, Frogs, LSC, Din connectors added at 1Y2 1Y2moreDinFuses.jpg
       Reply  Wed Nov 6 15:57:22 2013, Jenne, Update, LSC, Power Supply solution 
          Reply  Fri Nov 8 17:19:27 2013, Jenne, Update, LSC, New Broadband PD for POP 22/110 IMG_1255.JPG
             Reply  Sat Nov 9 10:25:43 2013, Koji, Update, LSC, New Broadband PD for POP 22/110 
                Reply  Tue Dec 17 14:06:59 2013, rana, Update, LSC, New Broadband PD for POP 22/110 POP22110sch.pdfPOP22110.pdf
    Reply  Thu Feb 26 16:37:21 2015, manasa, Frogs, LSC, RIP illegal power supply 
Message ID: 9363     Entry time: Sat Nov 9 10:25:43 2013     In reply to: 9361     Reply to this: 9481
Author: Koji 
Type: Update 
Category: LSC 
Subject: New Broadband PD for POP 22/110 

General Remarks on the BBPD

- To form the LC network: Use fixed SMD inductors from Coilcraft. SMD tunable capacitors are found in the shelf right next to Steve's desk.
  If the tuning is too coarse, combine an appropriate fixed ceramic SMC C and the tunable C (in parallel, of course)

- L1/C1a/C1b pads are specifically designed for an additional notch

- Another notch at the diode stage can be formed between the middle PD pin (just left of the marking "C3b") to the large GND pad (between C1a/C1b to C3a).
  You have to scratch off the green resin with a small flat screw driver (or anything similar)

- A notch at the amplifier stage can be formed between the output of MAR-6SM ("+" marking)  and one of the GND pads (left side of the "U1" marking)

- The original design of the PD is broadband. So additional notches on the diode stage provides notches and resonances.
  Check if the resonances do not hit the signal frequencies.

- One would think the PD can have resonant feature to reduce the coupling of the undesired signals.
  In some sense it is possible but it will be different from the usual resonant tank circuit in the following two points.

  * Just adding a parallel L between the cathode and ground does not work. As this DC current should be directed to the DC path,
    L&C combo should be added. In fact this actually give a notch-resonance pair. This C should be big enough so that you can ignore it
    at the target resonant frequency. Supply complimentary small C if necessary to keep low impedance of the Cs at the target frequency.
    (i.e. Check SRF - self-resonant frequency of the big C)

  * Since the input impedance of MAR-6SM is 50Ohm, the top of the resonant curve will be cut at 50Ohm. So the resultant shape looks
    like a bandpass rather than a resonance.

- So in total, simulation of the circuit is very important to shape the transimpedance. And, consider the circuit can not be formed as simulated
  because of many practical imperfections like stray Ls and Cs.

 

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