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Entry  Sat Nov 21 13:58:30 2020, Koji, Electronics, Characterization, Dark Current Measurement for InGaAs QPDs Q3000_dark_current.pdf
    Reply  Sun Nov 22 13:49:12 2020, Koji, Electronics, Characterization, Impedance Measurement for InGaAs QPDs impedance_measurement.pdfP_20201121_183830.jpgimpedance_test.pdfQ3000_impedance_test.pdf
       Reply  Mon Nov 23 23:17:19 2020, Koji, Electronics, Characterization, The dark noise of the Q3000 QPDs Q3000_dark_noise_81.pdfQ3000_dark_noise_82.pdfQ3000_dark_noise_83.pdfQ3000_dark_noise_84.pdf
          Reply  Tue Nov 24 10:45:07 2020, gautam, Electronics, Characterization, The dark noise of the Q3000 QPDs 
             Reply  Tue Nov 24 12:27:18 2020, Koji, Electronics, Characterization, The dark noise of the Q3000 QPDs 
Message ID: 403     Entry time: Sun Nov 22 13:49:12 2020     In reply to: 402     Reply to this: 404
Author: Koji 
Type: Electronics 
Category: Characterization 
Subject: Impedance Measurement for InGaAs QPDs 

To know any anomaly to the junction capacitance of the QPD segments, the RF impedances were tested with a hand-made impedance measurement.
All segments look almost identical in terms of capacitance.

Measurement setup:
The impedance of a device can be measured, for example, from the complex reflection coefficient (S11). To measure the reflection, a bidirectional coupler was brought from the 40m. Attachments 1 and 2 shows the connection. The quantity A/R shows S11. The network analyzer can convert a raw transfer function to an impedance in Ohm.

Calibration and Measurement limit:
The network analyzer was calibrated with 1) a piece of wire to short the clips 2) 50ohm resistor 3) open clips. Then the setup was tested with these three conditions (again). Attachment 3 shows the result. Because of the impedance variation of the system (mainly from the Pomona clip, I guess), there looks the systematic measurement error of ~1pF or ~25nH. Above 100MHz, the effect of the stray impedance is large such that the measurement is not reliable.

The setup was tested with a 10pF ceramic capacitor and this indicated it is accurate at this level. The setup is sufficient for measuring the diode junction capacitance of 300~500pF.

Impedance of the QPD segments:

Then the impedances of the QPD segments were measured (Attachment 4). The segments showed the identical capacitance of 300~400pF level, except for the variation of the stray inductance at high freq, which we can ignore. Note that there is no bias voltage applied and the nominal capacitance in the datasheet is 225pF at 5V reverse bias. So I can conclude that the QPDs are quite nominal in terms of the junction capacitance.

(Ed: 11/23/2020 The RF components were returned to the 40m)

Attachment 1: impedance_measurement.pdf  22 kB  | Show | Show all
Attachment 2: P_20201121_183830.jpg  4.739 MB  | Show | Show all
Attachment 3: impedance_test.pdf  817 kB  | Show | Show all
Attachment 4: Q3000_impedance_test.pdf  811 kB  | Show | Show all
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