Re: Why Adding a Voltage Amplifier after a Transimpedance Amplifier reduce BW? Book Claim by 0.64

Started by Felipe Jimenez May 14, 2015
On Thursday, May 14, 2015 at 4:08:04 AM UTC-7, Phil Hobbs wrote:
> >Oh and I'm fairly certain the non-inverting amplifier is wired up correctly. Between > >switching back and forth from the non-inverting to the inverting configuration > >several times, I am fairly certain that both configurations were wired up properly. > > Hmm... "several times" does make it sound like a solderless breadboard, as John suggested. Those things are slabs of misery, for sure. > > The AD8066 doesn't come in a DIP package, so I assumed it wasn't one of those things, but having bad layout strays is one of the ways to not build what you think you're building. > > Oh, one other thing--did you get your parts from an authorized distributor? Otherwise it's possible the op amp is counterfeit. > > (And do knock off the 'Dr.' bit--that's in my sig for SEO reasons. It's all free-men-and-equals round here.) > > Cheers > > Phil Hobbs
Sorry Phil...Still in grad school, so I'm just used to saying "Dr." if I don't know the person and I see those letters near their name. As for all the other replies including your own: The pnp C-multiplier guy was drawn wrong. Drew it last night. I know it was as we measured both +/-10V with a DMM and with a scope to check for oscillations. The whole circuit was built on piece of copper clad board. Made the job tight. Lifting input pins of the op amps off of the copper clad board. Used 0603 caps and resistors and 30AWG for connections. I will tell my co-worker to add another C-multiplier for the photodiode and to add some beefy caps on the supply pins. And to consider using single package opamps instead of dual package. Both of us (my co-worker and I) have Phil's book and AoE. Read through a little bit of each book (Ch 14 and 18 of Phil's and Ch 88 of AoE 3rd ed) plus a couple of papers of Phil's. Did the initial calculations for our design (I haven't really prototyped my balance PD yet) to ensure shot noise limited. and for the most part it works. The TIA worked nicely. It wasn't until he added the non-inverting amplifier did the BW decrease. Eventually, he switched to the inverting configuration and the BW issue disappeared and the noise results were satisfactory for the physicist that we're both doing our prototypes for. As for his specs: 50nW of light, PD: PC5-6-TO5, BW = 50kHz, light wavelength = 852nm