40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Thu Mar 4 19:53:56 2010, Alberto, Update, 40m Upgrading, 11MHz PD designed adjusted for diode's resistance; 55 MHz RFPD designed 6x
    Reply  Thu Mar 4 22:07:21 2010, rana, Update, 40m Upgrading, 11MHz PD not yet designed 
Message ID: 2656     Entry time: Thu Mar 4 19:53:56 2010     Reply to this: 2657
Author: Alberto 
Type: Update 
Category: 40m Upgrading 
Subject: 11MHz PD designed adjusted for diode's resistance; 55 MHz RFPD designed 
After reading this study done at LIGO MIT in 1998 I understood why it is difficult to define an effective impedance for a photodiode.

I read a few datasheets of the C30642GH photodiode that we're going to use for the 11 and 55 MHz. Considering the  values listed for the resistance and the capacitance in what they define "typical conditions" (that is, specific values of bias voltage and DC photocurrent) I fixed Rd=25Ohms and Cd=175pF.

Then I picked the tunable components in the circuit so that we could adjust for the variability of those parameters.

Finally with LISO I simulated transfer functions and noise curves for both the 11 and the 55MHz photodiodes.

I'm attaching the results and the LISO source files.

 

Attachment 1: rfpd55_Noise.pdf  44 kB  | Show | Hide all | Show all
Attachment 2: rfpd55_TF.pdf  12 kB  | Show | Hide all | Show all
Attachment 3: rfpd11_v2_TF.pdf  12 kB  | Hide | Hide all | Show all
rfpd11_v2_TF.pdf
Attachment 4: rfpd11_v2_Noise.pdf  43 kB  | Show | Hide all | Show all
Attachment 5: rfpd11_v2.fil  0 Bytes
Attachment 6: rfpd55.fil  0 Bytes
ELOG V3.1.3-