Recent content by kplee

1) What I understand is that there are two terminations: one at the scope with high impedance, and the other at the 50 Ohm termination with low impedance. If this is correct, why does the low impedance affect much even in the presence of the high impedance which is used for the detection? 2) If...

Okay. I was just not used to the language in this community since I am in physics and didn't have any chance to work on electronics before. I didn't mean to confuse you. I will keep it in mind. About what you said, I am kind of confused because when we think about the Ohm's law the voltage at...

Well, the thing is the signal already gets mixed up when passing through the DC blocker on the 50 Ohm side, as I showed you before (check the first pictures). I didn't even use the preamp yet.

Oh I see. I think I mixed up during the calculation. But somehow that doesn't make much sense since the optical input is around several uW, which corresponds to several uA. Anyway, I think that's not an important part for now. I can handle that later. The problem is how to match this signal with...

How does that calculation happen? I thought it can be directly converted from the PD datasheet, which implies the PD current of ~ 4.7 uA ideally.

1) I am not sure but I think it is working at least. 2) Sorry, 10mVpp

I am not sure whether I understand the coupling concept, but let me rephrase what you said in my version. 1. I coupled the PD signal directly to scope with BNC cable. I set the scope as DC coupling and saw ~ 3 Vdc offset (not 9, idk why) 2. I coupled the PD signal the same way as I did in 1)...

I will use the lock-in at the end, actually. The thing is, If I use only lock-in without preamp I would not see the signal. + I have no choice but to use it because this is what our lab has. haha

I mean, the test signal from photodiode made by test optical input.

It's the internal baatery

As I said, I want extract the AC signal out of DC background and amplify it using the preamplifier. What I am measuring now is a test signal, not a real signal which is way smaller than this.

I thought that applies for the scope, not for the termination load in the middle. Also, the datasheet is for the DC blocker, and in the picture I didn't even use the DC blocker. As I said, I tried to measure the signal with 50 Ohm termination and without DC blocker, which didn't work. Here is...

It's about the datasheet for DC blocker. The one I am using is 818-bb-21, and I think there is no information about the resistor. It says the VDC is 9 V, so i guess that is the bias voltage.

The main purpose of this is to amplify the signal with the preamplifier, and I thought DC background would ruin the amplification process if it dominates the real signal. As you might see the first pictures I uploaded, there is a huge DC background of ~ 5 V coming from photodiode (I actually...

So basically this is how I ended up with the 50 Ohm termination, and no signal was shown. I wonder what I have missed or mixed up in this setup.