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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
hboy007 wrote ...
the diode has 5 .. 6pF when biased with 15V and a rise/fall time of 50 .. 80ns, which sounds promising to me. Dark current is 4..20nA and current noise is 0.4 .. 1 pA / sqrt(Hz) - typical resp. maximum values. I'll be back with the calculations tomorrow. Thank you for your help!
Am looking forward to your lab results -- had never considered that position-senstive detectors could work so fast. Got some of these: Specified risetime is 1.5 us, but that's with 1k load instead of low impedance TIA.
As hboy knows, PSD's are unsurpassed for tracking a fast-moving light in one dimension. Spatial resolution equivalent to tens of thousands of pixels, and ( I see now ) "imaging rate" in the multi MHz. (to be honest, you don't get all of both parameters at once).
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
The first two National application notes that come up here talk specifically about using current feedback opamps as photodiode amplifiers:
Hopefully it helps a bit.
edit: While finding information on an unrelated topic (Miller Theorem) I found this good set of notes on high-speed transistor level linear amplifier design. It's not specifically applied to what you're doing but it covers the techniques you would probably need to use if you wanted to do a transistor level design instead of an opamp.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
I just found this paper about PSD array sensors:
it uses a different approach, placing an array of PSDs on a chip, just like this one here does it:
This definitively seems to be a hot topic in online 3d scanning, maybe we'll be able to see some applications of the type of scanner I had in mind when I started this thread.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Thoughts which may or may not be in the above references (ok, I haven't looked at them)
I assume that at some point there will be an ADC (or many/multiplexed for a linear array) So I'd expect 'best' performance if the photo-diode-current is integrated (capacitor, dV=dQ/C) during the SAMPLE period and reset (discharged) after the HOLD period.
If a linear array is used then I guess the 'key' will be physical construction so groundplane, smd components and whatever dense packages of cmos switches (S&H), ADC, mux, amplifier, &c. (and a quick look at rf stripline design) are called for.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
hboy007 wrote ...
the diode has 5 .. 6pF when biased with 15V and a rise/fall time of 50 .. 80ns, which sounds promising to me. Dark current is 4..20nA and current noise is 0.4 .. 1 pA / sqrt(Hz) - typical resp. maximum values. I'll be back with the calculations tomorrow. Thank you for your help!
Let's see the practical results:
and even more interesting, the C/V curve:
the capacitance at 0V is a bit random because there might be residual charges in the structure which dramatically change the actual zero voltage capacitance.
I felt like cooling the PSD down a little to make the leakage current look more promising. -20°C should be no problem with thermoelectric cooling. Coming up next: laser induced transient current measurements
5V bias voltage at -20°C would make for nice operating conditions, right?
ps. I bought 16 pc. of these PSDs to ensure the project will get anywhere soon.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
EL5167 OPA2683
Do these look suitable to you? Maybe it is the best solution to start with a G=20 .. 100 transimpedance amplifier stage. OPA2683 is available in a dual package so the CFB opamps will be matched to some degree.
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