Can You help me build TIA? - Page 1
Forum section: electronics / beginners

author: Zygo
author_rank: Newbie
timestamp: November 07, 2024, 10:54:40 am
content: I'm trying to build TIA, to measure response to X-rays/Gamma rays from small PIN diode.When gamma photons interact with the PIN diode, they generate electron-hole pairs in the semiconductor material. Each gamma-ray photon that hits the diode creates a pulse of current due to these generated charge carriers. So for better understanding, it would act just like normal photodiode interaction with visible light. The diode would be reverse biased to about 90V for electric field to accelerate the charge carriers. The diode in question would be BAR64-02EL.So response will be pulse of current/charge, and to my research the pulse would have about couple nanoseconds rise time and decay tail up to 1 μs. The capacitance of this diode is closely related to depletion region width, so it would decrease while the region increases. So reverse biasing the diode will increase this width and decrease capacitance from ~0.2pF to ~0.1pF or less.The max current amplitude of my pulse, according to my calculation would be around 0.2-1uA.I hoped to use OPA857 to build TIA to investigate the pulses with oscilloscope with in line capacitor to isolate bias DC voltage from TIA.I was hoping to use build in 20kΩ feedback resistor.For capacitance value I calculated Cf = Cin / RfCin - combination of Diode capacitance and amp input capacitance.So Cf ~80fF so i figured 0.1pF Silicon RF CapacitorIs designing/building TIA for so small pulses would be doable for a student, or would I need to consider many thinks designing PCB?I've made some simple PCB's for couple projects, but don't know much about line impedances, isolation and such topics.I would appreciate any comments and help if is it possible.I’m an medical physics student from Poland, so my understanding of electronics and English can be sometimes lacking.

author: tggzzz
author_rank: Super Contributor
timestamp: November 07, 2024, 11:15:57 am
content: Welcome to the forum; your English is fine, and better than many native English speakers.TIAs are discussed in The Art of Electronics 3, and in Phil Hobbs' bookhttps://electrooptical.net/Building_ElectroOptical_Systems/"Building electro-optical systems : making it all work" is directly relevant since "[it is] intended in the first instance for use by oppressed graduate students".Phil Hobbs is referred to several times in TAoE.Also search for "Phil Hobbs" on this forum.

author: jwet
author_rank: Frequent Contributor
timestamp: November 07, 2024, 12:30:35 pm
content: Here is a link to a good circuit by Bruce Denmark, an FAE for Maxim. Before Maxim, we both worked at SAIC and Bruce designed similar circuits for US Army Radiacs- handheld gadgets that measure Radiation. When we got to Maxim, he wanted to take a crack at redesigning it with these nice new Maxim op-amps. The Army circuit use a discrete JFET front end with a folded cascode and bunch of hot low current transistors. It had some other constraints- like being very Rad-Hardened.I googled the circuit and found the following link- its also buried on the Maxim web site. He does a good job of explaining the circuit- he is a great designer and still a Maxim FAE in the Northeast US if you want to look him up. Tell him John Wettroth says hi. I also included the basic schematic for lurkers.https://www.radiolocman.com/shem/schematics.html?di=653627

author: jwet
author_rank: Frequent Contributor
timestamp: November 07, 2024, 10:23:33 pm
content: I can help answer questions but I think it stands alone pretty well. A PCB is always a good idea and its cheaper and simpler than ever.