biff44
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Hi,
I don't know what you want me to explain.
A capacitor, a scope probe, a TIA, why a TIA improves fall time?
Everything already is explained. Do a forum search, do an internet search first.
If then still are questions you are welcome to ask a detailed question. Please refer to documents you have read, so we can discuss about it.
Klaus
I agree, nobody said so.input impedance of a transimpedance amplifier is NOT zero at high frequencies.
I will read this article and answer you.Op-Amp Transimpedance Amplifier
A transimpedance amplifier (TIA) converts a current to a voltage and is often used with current-based sensors like photodiodes. It’s also a common building block that helps explain the performance and stability limits of many other op-amp circuits.ultimateelectronicsbook.com
the input impedance of a transimpedance amplifier is NOT zero at high frequencies. so, where exactly do you expect that stored charge in the photodetector to go? to Disney world?
I want to use opa 354, which works at a frequency of 250 MHz. And then I use ad 8042, which works at a frequency of 160 MHz, for further amplification.Hi,
Please give values.
Every body has a different idea what "accurate" means.
If you are interested in timing, then an ADC might not be the best solution.
An ADC is mainly used to measure amplitude.
A comparator and a timer_capture will be more accurate and with higher resolution.
Klaus
Yes, you are right, it is better to use a timer for time measurements.Hi,
Please give values.
Every body has a different idea what "accurate" means.
If you are interested in timing, then an ADC might not be the best solution.
An ADC is mainly used to measure amplitude.
A comparator and a timer_capture will be more accurate and with higher resolution.
Klaus
What voltage are you talking?What is the lowest voltage I can give the 8042 ad amplifier?
Absolute input voltageWhat voltage are you talking?
Supply voltage? At which pin?
Absolute input voltage (range)?
Operable input voltage (range) in circuit?
Minimum detectable (AC) voltage that can be processed? Which frequency/timing/waveform.
In either case one needs to consult the datasheet. Either you or one of us.
hiHi,
Did you check the datasheet? What does it say?
Or you want us to do your job?
Klaus
You feel lost, lost in some details.I really do not know about amplifier parameters.
HiHi,
Very useful informations.
(Some pedantic notes: the main goal is to get emitted radiation timing. For this you don't read photodiode voltage (slow), but using a TIA photodiode current. The output of the TIA is voltage)
Calculation: if you want the TIA to generate 5V from 500nA, then the feedback resistor needs to be R = V / I = 10M.
I'd reduce it to get some margins. Maybe 4M7.
You need a careful PCB layout with proper GND plane for the whole circuit!
I'd realy try it as one stage at first.
It's likely that we need a second gain stage in future.
Use 0805 SMD resistor (maybe 0603) and short traces to get low series impedance.
Consider a compensating cap (0805 or 0603, COG/NP0) in the range of 1pF ... 10pF in parallel with the feedback resistor.
Try 3pF at first.
Do some tests on the TIA output with a scope. Use fast pulses from a LED directly on the photodiode. You will need some optical filter to get the desired 500nA.
Mind that the usual circuit TIA output has a DC offset and is inverted.
Maybe it is at 4.5V when dark and goes down to 0.5V when iluminated.
So far so good. Take some photos of your circuit and scope screen.
***********
For a two stage system maybe 20k feedback + inverting gain stage with gain of -200. Again: careful PCB layout is essential.
Don't forget power supply decoupling capacitors at each supply pin of each IC. Traces as short as possible.
Indeed this will be a challenge. Not very suitable for an electronics newbie.
Klaus
What comment do you expect?Please comment.
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