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Hi again!
The curves of Iout vs Vbias of the photodiode are specified up to 100uA. I'm working exceeding that value. I'm working around 1mA of Iout with 50 ohm load. You're right, there is no specification about light level. That's the point of my work because there is no any manufacturer that...
Hi Keith,
Thanks for your answer.
- The y axis is the transmitance in [V/V]. The output to input ratio, this is the sinusoidal wave output to the sinusoidal wave input of the generator. I'm using 200mVpk-pk amplitude.
- The photodiode is the Vishay BPW24R.
- I'm modulating the laser...
Hi Keith!,
How are you? I wish you a Happy new year!!
Finally I made the circuit with the OPA380 and I didn't found any problem with it. I realized the BW frequency cutoff is imposed by the photodiode due the high intensity it is exposed.
Please take a look at the attached graphic. You'll see...
Hi Rafael2323,
I was looking the same as you, but for lower frequencies (arround 100MHz), I have found the IC AD9660, which is specified up to 25 MHz
analog modulation. It's far from 2GHz you need but at least is a start. I think there are not much IC drivers for analog modulation, maybe you...
Hi Keith,
Thanks a lot for your answer.
I found this opamp OPA380 wich I realize is very similar to the THS4031 you recommended me.
I did the following configuration/simulation and think it will be ok for my project. In fact I was thinking to use the OPA2380 wich is a double OPA380. I think I...
Hi again Keith,
I'm trying to follow your suggestions about to use another slower opamp.
I couldn't find any of those you recommend me here in Argentina, but I have a few units of the following:
1.- LT1806CS8
2.- TSH350IDT
3.- **broken link removed**
4.- **broken link removed**
Could you...
Keith,
Just one doubt about the decoupling circuit you sent. What do you use as
the decoupling inductor 100nHy? Do you use a choke or chip ferrite?
Do you place it near the opamp pin ?
Thanks!
Horacio
Thanks for the image of the decoupling capacitors. I will try with that configuration.
I understand your point about voltage amplifications. It's a valid option I
don't discard. Nowadays I was considering the posibility to have two stages,
first TIA with lower Gain (1 or 2) and then a second...
Hi Keith,
Please see below. Thanks!
Ok, so I will solder 100nF and 100pF to decouple the source. Is that ok?
Yes you're right. Actually I put it just to show the way I'm using/biasing the photodiode. I think there is no difference to bias with negative or positive voltage and use the...
Hi again,
Today I have finally measured with spectrum analyzer and also the signal at the output of the device. Please let me clarify the devices I've been using and the corresponding measurements.
I build 2 devices that are the following:
Device Nr.1 --- Device Nr.2
---
Please note the...
Yes, I think you're right. Yesterday I've connected the second device (Rf=2.2k Cf=1pF no Tee) without laser signal and I saw a ~294MHz signal in the oscilloscope(BW=60MHz). I will check again with the spectrum analyzer to check the amplitude of it. So it's oscillating.
Could you please recomend...
Actually the bandwidth seems to be improved when optical attenuation is used (all the components of the signal are attenuated). I tested with several modulation index (without optical attenuation) and the bandwidth was not improved.
I will follow your suggestion.
Thanks!
Horacio
Hi Keith,
I've measured the output in both conditions with the oscilloscope (60MHz BW). The transmitance curve is on the original post.
I have control over the modulation. I'm using a diode laser that allow to control the modulation. It has a 50ohm input, so I connect the generator directly to...
Hi FvM,
Thanks for your help. Please see below.
Ah, ok. I used the same PCB design, same Opamp. But I used a 2.2k feedback resistor and only one feedback capacitor (1pF) instead of the C tee network.
Yes, when high input level light is used the gain drops starting at 100kHz, but if opticall...
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