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Entry  Tue May 3 04:09:53 2011, Koji, Update, LSC, REFL55 PD update REFL55.pdf
    Reply  Mon Jun 20 18:36:49 2011, Suresh, Update, LSC, REFL55 PD update REFL55_response.pdf
Message ID: 4845     Entry time: Mon Jun 20 18:36:49 2011     In reply to: 4605
Author: Suresh 
Type: Update 
Category: LSC 
Subject: REFL55 PD update 

[Suresh, Koji]

   I used a matlab code written by Koji to analyse the transimpedance and current noise data  of REFL55.  The details are in the attached pdf file.

Resonance is at 55.28 MHz:

Q of 4.5, Transimpedance of 615 Ohms

shot noise intercept current = 1.59 mA

current noise =21 pA/rtHz


Notch at 110.78 MHz:

Q of 54.8 Transimpedance of 14.68 Ohms.











[Rana, Koji]

REFL55 was modified. The noise level confirmed. The PD is now ready to be installed.


Kevin's measurement report told us that something was wrong with REFL55 PD. The transimpedance looked OK, but the noise level was terrible (equivalent to the shotnoise of 14mA DC current).

Rana and I looked at the circuit, and cleaned up the circuit, by removing unnecessary 11MHz notch, 1k shunt resister, and so on.

I made a quick characterization of the PD.

First page:

The transimpedance ws measured as a function of the frequency. The resonance was tuned at 55MHz. The notch was tuned at 110MHz in order to reject the second harmonics. The transimpedance was ~540V/A at 55MHz. (For the calibration, I believed the DC transimpedance of 50V/A and 10000V/A for the DC paths of this PD and #1611, respectively, as well as the RF impedance (700V/A0 of #1611.

Second page:

Output noise levels were measured with various amount of photocurrent using white light from a light bulb. The measurement was perforemed well above the noise level of the measurement instruments.

Third page:

The measured output noise levels were converted into the equivalent current noise on the PD. The dark noise level agrees with the shot noise level of 1.5mA (i.e. 22pA/rtHz). In deed, the noise level went up x~1.5 when the photocurrent is ~1.4mA.


Attachment 1: REFL55_response.pdf  13 kB  Uploaded Mon Jun 27 17:47:46 2011  | Hide | Hide all
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