Another (ultra)fast photodiode design circuit - Page 1
Forum section: electronics / beginners

author: stcoso
author_rank: Regular Contributor
timestamp: May 14, 2020, 10:40:23 am
content: Hi everyone...One year ago i was designing a TIA around a BPV10 pin photodiode (https://www.eevblog.com/forum/beginners/photodiode-circuit-design/) to monitor the light output from a LEDs driver that i've built. Since then i've learned a lot and designed other (faster) TIA with better opamps around the same photodiode (bpv10)to accomodate for my necessities (faster LEDs driver).Now i'm a bit stuck.Let's say i need to measure light waveforms in the uv region with pulse width of 1ns and peak irradiance at about 2(kW)/((m^2)(s)). How can i achieve this (other than buying a properly built product)? Can a circuit like this be designed to operate linearly (inside a 5% range) from dark to peak irradiance?What about linearity with respect to pulse width? Can be built to operate (linearly) even with continuos light waveforms?

author: tggzzz
author_rank: Super Contributor
timestamp: May 14, 2020, 12:46:00 pm
content: You should invest in Phil Hobb's bookhttps://www.electrooptical.net/Building_ElectroOptical_Systems/Alternatively, if you can ask a good and interesting question which doesn't look like you are merely after free consultancy, he may respond on usenet group sci.electronics.design.

author: stcoso
author_rank: Regular Contributor
timestamp: May 14, 2020, 01:47:09 pm
content: Thanks! I'm already looking at it!

author: jmelson
author_rank: Super Contributor
timestamp: May 14, 2020, 04:57:57 pm
content: Quote from: stcoso on May 14, 2020, 10:40:23 amYIKES! I hope you have a VERY small PIN photodiode, and very excellent circuit construction. This is going to be pretty tough!I never work with anything that fast, and generally anything with a risetime shorter than 10 ns gives me fits.Jon

author: stcoso
author_rank: Regular Contributor
timestamp: May 14, 2020, 07:27:58 pm
content: The photodiode is just the first (and probably the main) of a long list of problems... Especially for the UVA range.The BPV10 that I'm using has (from datasheet) 2ns rise/fall when opportunily biased.Looking at mouser/digikey/rs/farnell catalogues to find something suitable (rise/fall time and spectral range) led me to look at SiPM...

author: jmelson
author_rank: Super Contributor
timestamp: May 14, 2020, 11:48:39 pm
content: Quote from: stcoso on May 14, 2020, 07:27:58 pmSiPMs have a lot of small avalanche photodiodes paralleled with a series quench resistor. I think the quench resistor will interfere with the fast response you need. They have LOTS of gain for very low light levels, which doesn't sound like what you need.Jon

author: awallin
author_rank: Frequent Contributor
timestamp: May 15, 2020, 04:54:19 am
content: For simulating bandwidth and noise-floor I wrote some python scripts over here:https://github.com/aewallin/TIASimthey are based on the formulas in Hobbs and other references.So far I only built a ca 60 MHz BW detector with S5973 photodiode, OPA657 opamp, and RF 10 kOhm.I am building one withe HMC799 next, stay tuned... (https://www.analog.com/en/products/hmc799.html)The new TI opamps like OPA859 also look interesting (but WSON footprint is harder to solder), because they have lower input-capacitance than the older OPA657.For 1 GHz you probably need a photodiode with <1pF capacitance (at suitable bias), and an op-amp + layout with minimal input capacitance and parasitic capacitance over RF. Rumor has it that e.g. Thorlabs FDS015 and FDS025 are in fact Hamamatsu/other? photodiodes - so they might be available elsewhere also?If a 'digital' photoreceiver with just 0 or 1 output is suitable, then 1 Gbit SFP optics for telecom are dirt-cheap, and probably available for ~800nm, 1300nm, 1500nm. As a bonus the SFP has a TX channel also

author: stcoso
author_rank: Regular Contributor
timestamp: May 15, 2020, 10:10:13 am
content: I've a Si PIN photodiode candidate:https://www.hamamatsu.com/eu/en/product/type/S9055-01/index.htmlNot easy to find though

author: stcoso
author_rank: Regular Contributor
timestamp: May 15, 2020, 12:19:32 pm
content: Quote from: jmelson on May 14, 2020, 11:48:39 pmYep... The fastest SIPMs have got a fast output with sub-ns edge. But the fact that they're sensitive even to single photons is a problem. I've got something like 10^18 photon/m^2s

author: mcookieman
author_rank: Contributor
timestamp: May 15, 2020, 12:47:07 pm
content: Quote from: awallin on May 15, 2020, 04:54:19 amBeware that the input current noise is not white for FET input opamps...

author: khs
author_rank: Regular Contributor
timestamp: May 15, 2020, 02:27:12 pm
content: Quote from: stcoso on May 15, 2020, 12:19:32 pmI think there is no need for an amplfier.Just connect some reverse voltage to the diode and connect it directy to the 50 Ohm input of your oscilloscope.

author: Marco
author_rank: Super Contributor
timestamp: May 15, 2020, 03:57:52 pm
content: Why would you need a transimpedance amplifier with 0.5 pF of capacitance? Can't you just feed it directly to a high gain 50 Ohm matched MMIC?50*0.5e-12 doesn't seem a relevant RC time for a couple GHz signal.

author: stcoso
author_rank: Regular Contributor
timestamp: May 16, 2020, 08:59:02 am
content: Quote from: khs on May 15, 2020, 02:27:12 pmQuote from: Marco on May 15, 2020, 03:57:52 pmInspired by both of this comments i tried with the bare BPV10 pin photodiode that i have at hand. When biased at 50V it as a 2pF Cj (with 50 Ohm is -3dB at 1.6GHz)... It actually works better than i remember but show it's limits with less than 0.05A/W at the wavelenght of interest.I'll look into MMIC.Thank you all.