I am using OPA657 as transimpedance amplifier. I have the photodetector as the input. When there is no input from the laser (even if the photodetectors are closed with no light coming in) the output of the opamp oscillates between -5 and +5V. Does anyone know why that is or what could the problem be? The circuit is working and producing reasonable output when the laser gives the signal. The exact same circuit with OPA655 does not have this problem. I am using all SMD components.
Thanks, Vitaliy
Try a small series R between the summing node and the photodiode.
...Jim Thompson
Hi Jim, what about that method of putting an RC between the -i/p and ground to boost the HF gain a bit. Does it work with trans Z amps? Never had to use it myself, been lucky, maybe
martin
My guess is the problem is capacitance to ground from the summing node... i.e. a *big* photodiode... R isolates the capacitance.
...Jim Thompson
I don't think many audio guys use photodiodes that often, unless its in a spectro thingummy to work out the quality of their coke.
martin
The OP said, "I am using OPA657 as transimpedance amplifier. I have the **photodetector**..."
...Jim Thompson
Jim is right, I have photodetectors. 50Ohm resistor between the output of opamp and rf connector did the trick.
Thanks, Vitaliy
Hang on....
Jim told you to put the resistor between the photodetector and the input of your amplifier.
You have just said that you stuck the resistor on the output to isolate it from some cable that takes the signal elsewhere.
Well, whatever.... I mean this out of date chicken pie tastes a bit fruity but I have a spare toilet roll for the morning.
DNA
My local bar gets 10Kg of snails a day, they boil them up with fresh herbs and stuff and sell to the locals.
There are about 30 bars here... Thats an awful lot of shells left over
martin
Is this some sort of reference to that film where the girly says 'Let's lick Arse'. You know, the one without Bruce Willis in it..... bugger 'Demolition Man'. There you go, I wouldn't want anyone to suffer.
Anyway.
So lettuce growing has no returns these days so what you do is grow a plot and then sprinkle some snails at one end at the age of 20. Then you make your way down the other end, as they munch their way through it. Harvest the buggers at 68 and retire on the proceeds.
DNA
fruity
lick
'Demolition
Wasn't that a Sylvester Stallone movie?
the
Opps too late in the night - I missed the "without" part :-( - time to get some sleep!
plot
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