Hello Community,
I am facing a problem while building an amplifier for a Photodiode in Photovoltaic mode.
I have connected a few photodiodes in series; then I applied a high-pass filter. Now I want to amplify the voltage signal across R3 (in the figure). I went with a non-inverting amplifier design with a comparator.
The problem I am facing is that during the first few micro second, the output of the comparator is like this:


That is because if I compare the inputs of the comparator:



So I am asking for some help for the betterment of my design.

 

The problem is too high op-amp slew rate and speed of comparator transitions.
You can use faster op-amp or do it with transistors.

 

Hello Community,
I am facing a problem while building an amplifier for a Photodiode in Photovoltaic mode.
I have connected a few photodiodes in series; then I applied a high-pass filter. Now I want to amplify the voltage signal across R3 (in the figure). I went with a non-inverting amplifier design with a comparator.
View attachment 349014 The problem I am facing is that during the first few micro second, the output of the comparator is like this:
View attachment 349015

That is because if I compare the inputs of the comparator:

View attachment 349016

So I am asking for some help for the betterment of my design.

That is what happens as C2 charges up to the photodiode voltage.
Is what happens in the first few microseconds important?

 

Photovoltaic? Why not use photoconductive?

Search for trans impedance amplifier for photodiodes.
The circuit not only will be simpler, but it will be orders of magnitude faster and with improved range.

EDIT: and you won’t require a DC gain of 5000X.
EDIT 2: the OPA380 is already a trans impedance amplifier. Use the datasheet circuits and recommendations. Don’t re-invent the wheel.

 

Photovoltaic? Why not use photoconductive?

Search for trans impedance amplifier for photodiodes.
The circuit not only will be simpler, but it will be orders of magnitude faster and with improved range.

EDIT: and you won’t require a DC gain of 5000X.
EDIT 2: the OPA380 is already a trans impedance amplifier. Use the datasheet circuits and recommendations. Don’t re-invent the wheel.

Many thanks for the reply. I have to use photovoltaics since I want to see the possibility of harvesting energy. Accepting this condition, how can I improve the circuit?
NB: Being faster is not my priority.

 

That is what happens as C2 charges up to the photodiode voltage.
Is what happens in the first few microseconds important?

I want to decode a message sent by the transmitter. Probably not urgent to have them, but it would be better to have them.

 

The problem is too high op-amp slew rate and speed of comparator transitions.
You can use faster op-amp or do it with transistors.

Its slew rate is 80V/microsecond. I think it is fast enough.

 

I want to decode a message sent by the transmitter. Probably not urgent to have them, but it would be better to have them.

But if you are trying to receive a pulse every 16us, you do need some speed. How is the message sent?

 

But if you are trying to receive a pulse every 16us, you do need some speed. How is the message sent?

By an LED, simple OOK light modulation for now. The message can be slow for this prototype

 

By an LED, simple OOK light modulation for now. The message can be slow for this prototype

If the circuit is already running then there won't be a problem, because it will already have gone through the start-up charging of the capacitor.
If you are trying to use a photovoltaic panel to receive the signal, don't forget the size of the junction capacitance!

 

If the circuit is already running then there won't be a problem, because it will already have gone through the start-up charging of the capacitor.
If you are trying to use a photovoltaic panel to receive the signal, don't forget the size of the junction capacitance!

Thank you, i will keep in mind

 

Its slew rate is 80V/microsecond. I think it is fast enough.

I have to use photovoltaics since I want to see the possibility of harvesting energy. Accepting this condition, how can I improve the circuit?
NB: Being faster is not my priority.

.
These are two conflicting requirements.
But Ok then, I am Signing off.

 

.
These are two conflicting requirements.
But Ok then, I am Signing off.

The first statement is not a requirement. I was stating that my amplifier is fast enough, as its slew rate is good enough.

 

The circuit analysis is made much less easy because of showing it as a wiring diagram instead of using correct symbols. And the boxes with numbers AR NOT the correct symbols!!
And certainly the comments in posts #2 and #3 are valid. And also the comment in post #4.