I'm building a optical comm. circuit using an AD8015 transimpedance amplifier from Analog Devices. Datasheet:
Here is the circuit I'm using:
I'm having trouble with the circuit producing a strong ~1.9MHz oscillation. This is independent of what the circuit is hooked to. I have tried it with several different photodiodes (and no photodiode) and it doesn't seem to have a big effect.
Thoughts on why this is occurring?
c.pdf
It's probably your PCB design.
Leon
tic.pdf
Try to slow it down if you can.....
Read Jim Williams' AN47:
-- John Devereux
Datasheet:
using:
What do you mean by, "slow it down?"
Post a pic of the actual layout!
John
I don't know this TIA chip because I usually roll my own but TIAs do not like much capacitance from their input pin to ground. If it's much above a pf for a fast TIA they can go berserk. What you could try is to either lower the stray capacitance at the input or provide a small capacitance (fraction of a pf) from inverting input to output. IIRC the AD8015 is diff-out so you'd have to figure out which output to use.
While I am an advocate for a full ground plane you might have to create a small void in it around the input pin in order to minimize capacitance. If the layout is already done you could try to lift the input pin, bend it up and solder the PD to it that way. And no long cables or traces there. If you can yield enough stability margin that way it would be time for a re-layout.
-- Regards, Joerg http://www.analogconsultants.com/
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