High speed Transimpedance amplifiers

[Marco]

The OSLRF-01 (open source laser range finder) used a MAX3658.

[tggzzz]

If this is a LIDAR application, then I would raise the issue of stray light. Any light that gets to your photodiodes other than the pulse signal reflected from the target will cause trouble. Even if you use (as you should) some form of synchronous detection, stray light will add its contribution to the shot noise, and in many cases this can completely overwhelm all other noise sources (as well as risking saturating the TIA). You should look at using optical filtering to remove light outside the operating waveband - but remember that narrow-band filters are designed to work with normal incidence light. You may have difficulty matching the source & filter wavelengths for very narrow bandwidths, such that one or other may need to be temperature-tuned. The receiver optics & housing need to be designed to allow this. Also take great care when designing your internal and external baffling.

Despite the warnings from @tggzzz and @grouchobyte (and I have personally encountered this issues they raise), APD's can be made to work well. But they are 'difficult', and generally most applicable in situations where the light level is very low, and you are struggling for every photon, even if you aren't actually trying to count them.

Just so.

@tggzzz: have you come across SiPMT's? Basically an array of Si APDs operating in Geiger mode and wired to a common output. They can be used for photon-counting, but seem to be restricted to shorter wavelengths so not much use to us here.

I'm not familiar with that term, since I last looked at the topic in ~1980/81 I certainly wasn't interested in an array, since that wouldn't have been of any use in an optical TDR for the new-fangled single mode optical fibres.

Looking at https://en.wikipedia.org/wiki/Single-photon_avalanche_diode makes me think the current terminology for the design would have been a standard APD operating in a passively-quenched-SPAD configuration. It wasn't developed since my company was interested in field test equipment, and Peltier cooling wasn't up to the job.

[tggzzz]

Hi guys, interesting topic with interesting comments especially from grouchobyte and tggzzz, I guess I won't be using those Perkin Elmer APDs then, don't know the part number, can't find them at the moment. I was looking at developing a LIDAR range finder for use up to say 1 meter, modulate a 25mW or 30mW 660nm or 690nm laser diode at around 300MHz or 350MHz and determine distance by measuring the phase of the returned signal. To keep out ambient light I would use a small band pass filter, 10nm or so wide, in front of the photo detector. Optically it would be something like "A twofold modulation frequency laser range finder" available on CiteSeerX. The laser modulation is the easy bit but what about the detector, PIN diode maybe followed by a MMIC ?

Definitely not eyesafe, then. I'd hate to be debugging and experimenting with such a system!

You might like to consider using millimeter wave technology. There are ISM bands around there, the components are becoming available (unlike in 1996), and companies are actively developing RADARs for inter-vehicle use.

[max_torque]

I can't say too much, but i'm not responsible for what happens downstream of the preamplifier for the diode(s), but yes, there is a load of DSP stuff that is all hush hush and secret squirrel at the moment. The system is a research project, and it's sorta close to being an optical pulse doppler radar, kinda.  At the moment, it's "Lab based" demo only, and currently uses a horrendously expensive front end, which i am trying to replace with a much cheaper alternative to allow systems to be built for real world testing etc.  I hope to be able to get a teardown on the current front end to see what components that is running and how to best replace it   

[TerraHertz]

... there is a load of DSP stuff that is all hush hush and secret squirrel at the moment.  ... and it's sorta close to being an optical pulse doppler radar, kinda.  ...

Optical eavesdropping, via doppler reflection from surfaces near the conversation?
Or optical missile guidance, for defeating radar-stealth and thermal decoy systems.

[bobaruni]

The laser modulation is the easy bit but what about the detector, PIN diode maybe followed by a MMIC ?

Chris, what about this?
https://www.maximintegrated.com/en/products/comms/optical-communications/MAX3970.html

Or with this, you might be able to get away without a narrow band optical filter as it's AC coupled.
https://www.maximintegrated.com/en/products/all-products/archive/MAX3660.html

By the way, where can I get my hands on a semi-flexible (not glass) narrow(ish) band optical band pass filter for about 940nM?
Sorry if I'm hijacking but we have a few experts all in the one place

[chris_leyson]

Thanks bobaruni, I will look into the Maxim transimpedance amplifiers. Better not hijack max-torques thread anymore. BK Interferenzoptik and Envin Scientific are two companies that we buy bandpass filters from. Even got a part number for a BK 840nm filter

http://www.interferenzoptik.de/900nm-1550nm_en.htm

they're not cheap though.

Definitely not eyesafe, then

Don't worry tggzzz got my OD4 safety glasses, power will probably be 10 to 15mW by the time the laser has gone through the optics path and protective windows. It's intended for a welding environment and I need a spot measurement hence the laser.

[tggzzz]

Thanks bobaruni, I will look into the Maxim transimpedance amplifiers.

Before spending too much time on any Maxim part, check its price and availability using RS, Farnell, Digikey, Mouser, octopart, findchips

[chris_leyson]

Thanks tggzzz I had forgotten about Maxim and the lack of availabilty.

[bobaruni]

Yep, a lot of Maxim stuff is EOL or very hard to find, but OK if you're not trying to build commercial quantities.

@Chris, thanks for the heads up about the filters

[Marco]

For a fully integrated transimpedance amp what's the alternative? TI is good at keeping their stuff in stock, but anything decent is die/wafer. Maxim seems the only one putting a decent transimpedance amplifier in a normal SMD package.

I wonder if you could combine a FET+PNP combo as a discrete transimpedance amplifier, FET for the current noise and BJT for the gain.