Opamp recommendations - Page 1
Forum section: electronics / projects

author: dbvanhorn
author_rank: Newbie
timestamp: August 29, 2018, 06:04:10 pm
content: I'm looking for an opamp that is low noise (comparable with discrete transistors like BC847B), and will give me 35dB or so gain at 500kHz. The application is very narrowbanded but the opamp will be dealing with the raw antenna input with an impedance of about 250 ohms. All this fun needs to happen with a single 3V supply. Small footprint, single opamp per package is ideal.Hey, a guy can wish.. Any ideas?

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 29, 2018, 06:13:32 pm
content: How about this?http://www.ti.com/product/lmh6629They draw quite a bit of current (15.5 mA, it's all relative) but they are fantastic. Probably overkill in terms of BW.

author: ogden
author_rank: Super Contributor
timestamp: August 29, 2018, 06:13:50 pm
content: Quote from: dbvanhorn on August 29, 2018, 06:04:10 pmAny schematics?

author: dbvanhorn
author_rank: Newbie
timestamp: August 29, 2018, 06:34:47 pm
content: Not yet.

author: dbvanhorn
author_rank: Newbie
timestamp: August 29, 2018, 06:35:52 pm
content: That actually might work. The noise is higher than I'd like, and they are not cheap, but I'm going to get a few and see how they do in circuit.Thanks.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 29, 2018, 06:59:20 pm
content: ... what about a silicon MMIC ?

author: dbvanhorn
author_rank: Newbie
timestamp: August 29, 2018, 09:03:01 pm
content: Any specific suggestions?

author: Wolfgang
author_rank: Super Contributor
timestamp: August 29, 2018, 09:25:24 pm
content: INA02186 could be tried. See the curves. Gain is ample, so LV operation with a rather small resistor should be OK.I used this one (at 5V) for a lot of low noise jobs:https://electronicprojectsforfun.wordpress.com/rf-module-gallery/the-amplifier-module-gallery/mmic-amplifiers/an-ina02186-mmic-amplifier/

author: dbvanhorn
author_rank: Newbie
timestamp: August 29, 2018, 09:52:57 pm
content: Looks like the low voltage cutoff is 4V which is more than I have available.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 29, 2018, 09:58:02 pm
content: When you bias for 25mA, everything should be fine.You probably dont want 30dB of gain anyway.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 29, 2018, 11:01:01 pm
content: Since your gain requirement is pretty high, I'd do it in two stages or more, 50MHz GBP gets you 20dB of gain at 500kHz, so trying to do it in a single amp means you need an absurd GBP, but doing it in two stages you can find some reasonable amps for, and doing it in 3-4 stages will get you a lot more options in terms of inexpensive low noise amps. Something like a 3 stage amplifier would let you use 8MHz GBP opamps, for which low noise variants can be had reasonably inexpensively, with 12dB of gain at each stage, in fact, you could just look for decent quality audio opamps and use them. The trickier part is the 3V supply, but there are plenty of options given the popularity of those lower voltages in mobile and low voltage devices, so find at least 9.5V/us slew rate or so if you need a full scale output and look for something rail-to-rail to utilize it fully and use at least 2 stages to do your amplification.If you really need that 35dB to happen in a single stage, something like a MMIC is a much better choice, but a small 8 pin TSSOP with two opamp elements and a few passives wouldn't be enormous and should do the job reasonably.

author: palpurul
author_rank: Regular Contributor
timestamp: August 30, 2018, 12:19:16 pm
content: ADA4895It's a low noise opamp. 1nv/sqrt(Hz) input voltage noise. Quite low. It's got a lot of bandwidth, about 200MHz at 10V/V gain. Only problem is it can be operated with 3V minimum. It's worth looking into I think.Link to the opamp