Hello guys..
I want to design a trans-impedance amplifier to detect currents of the APD (in the range of 200 nA to 100 micro A).
Could some one suggest me the best IC with less bias current, single supply (+5 V only) and how to design a high sensitive TIA..? (typically, for every 100 nA change in the current, 100 mV voltage should be displayed).
Hello Guys..
Could you please help me in designing a trans impedance amplifier with single supply...?
Then 100 uA will make 100 volts.
You'd have to range switch or something.
Do you have access to Phil Hobbs' book?
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Hello H=Jhon Lerkin, Thanks for your swift response.. Well I don't have access to Phil Hobbs' book.. And whatever the maximum current I can detect upto 5V ...that is fine... But I am worrying about how to choose the suitable opamp and design parameters....
Start simple with something like an LMP7701 and 1Meg feedback resistor.
Get or borrow a copy of Horowitz and Hill "The Art of Electronics" the
3rd Edition.piglet
+1 for AoE3.. chapter 8.11 does a nice job of talking about TIA's. (On a more basic level than Phil's book.)
To the OP the next question is how much speed /BW you need? (and what's the input C of your APD?)
George H.
???
What sort of bandwidth/response time do you need?
What is the photodiode bias voltage?
What is the photodiode capacitance?
Here's Phil's appnote on low-noise TIA's. There's more in his book.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Well....Bandwidth required is 1 MHz.. APD biasing voltage is 26-30V. Photodiode capacitance is 5pF
How about the OPA380 ? But my fastest opto TIA is only few kHz.
piglet
Yes...bandwidth is the constrain in this case...and bias current as well..
Huh, yeah something like that. To the OP, Putting in "rough" numbers. Say 1 Meg of feed back R, and another ~5pF of stray and opamp input C. So 1 Meg ohm*10 pF = 10^-5 sec, ~10^4 Hz (2*pi =~ 10) You'll need about a 100MHz GBW opamp. piglet's suggestion look good.
George H.
The 1 meg feedback resistor and the 10 pF of capacitance put a 10 microsecond tau, 16 KHz, lowpass filter INSIDE the opamp feedback loop. That will make it ring like hell or oscillate, and will make a gigantic noise spike.
Adding a cap across the 1M feedback resistor is the classic/clumsy/slow way to avoid the stability and noise crisis. Phil's paper and book discuss this.
A good TIA will have 100x the bandwidth of the obvious one.
APDs have a lot of internal gain, and are inherently noisy, so it might be OK to use a fast low-transconductance stage followed by a voltage amp or two.
I'm playing with a couple of new TIA circuits now, just for fun, one being a cascode+MMIC thing. There are some amazing MMICS around lately, TIAs that aren't identified as such. Of course, that circuit will be AC coupled, so I'd need to embellish it if I want DC response.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Grin.. yeah, killing any oscillation and measuring the noise will be his problem. I was just trying to flesh out the details of how piglet picked the OPA380
Classic, clumsy and slow, pretty much describes my approach to circuit design. :^) I haven't done a TIA in a while but the stray ~0.1pF of the 1 Meg FB resistor may be enough to stabilize it.
I've never used an APD... I did buy a few from DK. I buy fun parts, and then don't have time to play with them.
George H.
Its input bias current is high. It will rail with a 1M feedback resistor. Input current noise is correspondingly high.
They have a lot of gain... approaching infinite as you crank the voltage up... but they are noisy and temperature sensitive.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Oops.. my spec sheet says 50 pA.. that seems fine.
I really want to bias an APD above the breakdown voltage and see if I could use it as a SPAD. (Geiger-Muller mode) It will probably stink.
George H.
I probably typoed the part number. I never learned to type.
That will just about do what he wants in a single stage. There is still a voltage swing crisis at 100 uA.
Switching the feedback resistor has its own issues!
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Let me say why am looking for new design.. We are currently using the receiver module which has three stages:
Well...we used LM2662 as a -5V supply.. Here on we could see the hell noise below 100kHz.. I couldn't get rid of this noise by using bypass caps..but I could just reduced it.. Yet there is a lot of noise all across the circuit ranging from few kHz to hundreds of MHz...
is the link where I have uploaded couple of documents..
I really don't know what sort of noise it is and from where it is coming....
Let me say why am looking for new design.. We are currently using the receiver module which has three stages:
Well...we used LM2662 as a -5V supply.. Here on we could see the hell noise below 100kHz.. I couldn't get rid of this noise by using bypass caps..but I could just reduced it.. Yet there is a lot of noise all across the circuit ranging from few kHz to hundreds of MHz...
are the links where I have uploaded couple of documents..
I really don't know what sort of noise it is and from where it is coming...
Well, if you're connecting a photodiode directly to a SMPS, what did you expect?
Hint: Taking a spiky supply rail, differentiating it with a small capacitor, and sticking the resulting current into a high-gain current amplifier may not be what you want to do.
Of course, three lines of algebra would have told you what the results were going to be, and you'd have learned something instead of just throwing spitballs. This theory stuff really works. ;)
We've had several threads about capacitance multipliers recently, including one where I posted an LTspice schematic of a 2-stage cap multiplier that will knock that stuff down by about 180 dB, assuming that you have adequate RF shielding.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
He could start with a simple RC filter on the bias supply... that might be enough to show him where the problem is. (My hint is to look at the noise on the bias voltage and see if it looks the same as your signal noise.)
It is weird how this started as a thread to find an opamp.
To the OP, do you have any thermal regulation on the APD? I've read that the gain is a strong function of the bias voltage and temperature.
George H.
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