> I'm building a optical comm. circuit using an AD8015 transimpedance
> amplifier from Analog Devices. Datasheet: http://www.analog.com/UploadedFiles/Data_Sheets/AD8015.pdf
>
> Here is the circuit I'm using: http://gallamine.com/photodiode_tia_schematic.pdf
>
> 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?
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/
Reply by John Larkin●March 17, 20082008-03-17
On Mon, 17 Mar 2008 11:45:22 -0700 (PDT), williamcox@gmail.com wrote:
>I'm building a optical comm. circuit using an AD8015 transimpedance
>amplifier from Analog Devices. Datasheet: http://www.analog.com/UploadedFiles/Data_Sheets/AD8015.pdf
>
>Here is the circuit I'm using: http://gallamine.com/photodiode_tia_schematic.pdf
>
>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?
Post a pic of the actual layout!
John
Reply by ●March 17, 20082008-03-17
On Mar 17, 4:13 pm, stp <slave...@gmail.com> wrote:
> On Mar 18, 8:38 am, Leon <leon...@btinternet.com> wrote:
>
>
>
> > On Mar 17, 7:45 pm, william...@gmail.com wrote:
>
> > > I'm building a optical comm. circuit using an AD8015 transimpedance
> > > amplifier from Analog Devices. Datasheet:http://www.analog.com/UploadedFiles/Data_Sheets/AD8015.pdf
>
> > > Here is the circuit I'm using:http://gallamine.com/photodiode_tia_schematic.pdf
>
> > > 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?
>
> > It's probably your PCB design.
>
> > Leon
>
> Try to slow it down if you can.....
What do you mean by, "slow it down?"
Reply by John Devereux●March 17, 20082008-03-17
williamcox@gmail.com writes:
> I'm building a optical comm. circuit using an AD8015 transimpedance
> amplifier from Analog Devices. Datasheet: http://www.analog.com/UploadedFiles/Data_Sheets/AD8015.pdf
>
> Here is the circuit I'm using: http://gallamine.com/photodiode_tia_schematic.pdf
>
> 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?
On Mar 18, 8:38=A0am, Leon <leon...@btinternet.com> wrote:
> On Mar 17, 7:45=A0pm, william...@gmail.com wrote:
>
> > I'm building a optical comm. circuit using an AD8015 transimpedance
> > amplifier from Analog Devices. Datasheet:http://www.analog.com/UploadedF=
>
> > 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?
>
> It's probably your PCB design.
>
> Leon
Try to slow it down if you can.....
Reply by Leon●March 17, 20082008-03-17
On Mar 17, 7:45=A0pm, william...@gmail.com wrote:
> I'm building a optical comm. circuit using an AD8015 transimpedance
> amplifier from Analog Devices. Datasheet:http://www.analog.com/UploadedFil=
>
> 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?
It's probably your PCB design.
Leon
Reply by ●March 17, 20082008-03-17
I'm building a optical comm. circuit using an AD8015 transimpedance
amplifier from Analog Devices. Datasheet: http://www.analog.com/UploadedFiles/Data_Sheets/AD8015.pdf
Here is the circuit I'm using: http://gallamine.com/photodiode_tia_schematic.pdf
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?