Where can I get a reasonably priced high speed photodiode amplifier? - Page 1
Forum section: electronics / testgear

author: Ben321
author_rank: Frequent Contributor
timestamp: August 21, 2021, 10:34:51 pm
content: I would like to get an amplifier designed to operate a photodiode in its faster current-source mode (not slower photovoltaic mode). I think these are called transimpedance amplifiers, and convert the photodiode current to a voltage output that can then actually be captured with an analog to digital converter. I am hoping to get a high-speed transimpedance amplifier (several megahertz bandwidth) because I would like to be able to send analog video from an LED (the easier part of this experiment) over a light beam to a photodiode to be converted into a voltage (the hard part, due to the need for a high speed transimpedance amplifier, and the generally high price of such amplifiers). Do you know of any company that makes low-priced high speed transimpedance amplifiers for the electronics hobby community?

author: bdunham7
author_rank: Super Contributor
timestamp: August 21, 2021, 10:42:18 pm
content: Gain, bandwidth and low noise. Pick any two!https://e2echina.ti.com/cfs-file/__key/telligent-evolution-components-attachments/00-52-00-00-00-00-16-19/Transimpedance-Considerations-for-High_2D00_Speed-Amplifiers-_2D00_-sboa122.pdf

author: tggzzz
author_rank: Super Contributor
timestamp: August 21, 2021, 11:27:18 pm
content: These are discussed in The Art of Electronics 3, an in Phil Hobbs' bookhttps://electrooptical.net/Building_ElectroOptical_Systems/

author: TimFox
author_rank: Super Contributor
timestamp: August 22, 2021, 03:14:41 am
content: The classic textbook on photodiode amplifiers:https://www.amazon.com/Photodiode-Amplifiers-OP-AMP-Solutions/dp/007024247X/ref=asc_df_007024247X/?tag=hyprod-20&linkCode=df0&hvadid=312031082787&hvpos=&hvnetw=g&hvrand=15142538664731941357&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021734&hvtargid=pla-454779932308&psc=1

author: Marco
author_rank: Super Contributor
timestamp: August 22, 2021, 03:51:59 am
content: LTC6560 is about the fastest you're going to get with a solder-able integrated TIA (the faster integrated TIAs are in die form and the GHz opamps won't do any better).

author: StillTrying
author_rank: Super Contributor
timestamp: August 22, 2021, 10:15:41 pm
content: Quote from: Ben321 on August 21, 2021, 10:34:51 pmI think analogue video speeds through a LED are near enough impossible, a few of us have tried and got stuck around 300 kHz which is about 30 times too slow for analogue video.https://www.eevblog.com/forum/beginners/floating-probe!-for-$2-50/

author: StillTrying
author_rank: Super Contributor
timestamp: August 22, 2021, 10:23:16 pm
content: Quote from: Marco on August 22, 2021, 03:51:59 amI've got one and don't think it's solder-able, by me, I would probably have a large via in the middle of it and solder the ground from underneath.They're only linear 0 to 25uA before they limit, up to 1mA, I think they're really just for pulse use.

author: Marco
author_rank: Super Contributor
timestamp: August 23, 2021, 07:43:58 am
content: Quote from: StillTrying on August 22, 2021, 10:23:16 pmThey also have a relatively high transimpedance gain and low noise. It can hardly output above the supply rail.If say daylight exposure would cause too much current you can just use a dark glass to attenuate it, your dynamic range is going to suck regardless, a different TIA won't help much.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 23, 2021, 08:40:58 am
content: Quote from: Ben321 on August 21, 2021, 10:34:51 pmIn theory that should work, in practice there's not much chance in sending analog video with light. The best approach would be to use pulsed/chopped light, AM modulated with the video signal.Why does the sent video has to be analog? Is this for a hobby/learning learning project, or for a commercial design (which needs to be reproducible and reliable)?

author: StillTrying
author_rank: Super Contributor
timestamp: August 23, 2021, 12:28:52 pm
content: When I've been aiming a bright LED and a photo diode at each other over distances of 2 to 25cm and looking at the analogue light level half the time it works as a vibration detector because of the beaming, any movement on a wooden floor or even a neighbour slamming a door or window is picked up.Those IR headphones that fill the room with IR seem to work well enough even when you're moving about but with occasional dropouts that sound analogue like, but I think they must be done with digital pulses, because of the varying level as you move about.I'd have a look at the IR light shape if I had them.I'll simulate a LTC6560 again, when I'm doing nowt.

author: SeanB
author_rank: Super Contributor
timestamp: August 23, 2021, 01:03:19 pm
content: IR headphones typically use FM modulation at around 80-100kHz, and use a very narrow 1-2A 2us current pulse to drive the IR emitter LED units, so there is a very strong signal. Receiver wise there is a photodiode behind an IR pass filter, and amplification and a simple FM demodulator to recover the audio. Stereo is done using the same as FM radio, 19kHz pilot tone, and the same sum and difference signals on the carrier, though he bandwidth of the difference signal is hard limited, and the receive side uses an almost standard stereo decoder chip to get it back. However most are mono audio, better range and lower noise, typically used for TV set listening without wires.

author: Marco
author_rank: Super Contributor
timestamp: August 23, 2021, 04:36:35 pm
content: Quote from: StillTrying on August 22, 2021, 10:15:41 pmThis paper has basic link getting 25 MHz with an IR LED, the LED is no longer available, but there are other infrared LEDs with similar tr/tf values in the datasheet.https://repository.tudelft.nl/islandora/object/uuid:3103320d-d02b-43fc-826c-6d7733f908d5/datastream/OBJ/download

author: RoGeorge
author_rank: Super Contributor
timestamp: August 23, 2021, 06:19:35 pm
content: The one in the paper does not sendanalogvideo, it's a multichanneldigitalbroadcast.

author: Marco
author_rank: Super Contributor
timestamp: August 23, 2021, 07:01:59 pm
content: They measured a simple circuit of just the LED driver and the TIA to test the bandwidth.

author: StillTrying
author_rank: Super Contributor
timestamp: October 04, 2021, 04:01:49 pm
content: http://www.modulatedlight.org/optical_comms/LED_AM_video_link.html