10x amplification of 10MHz? - Page 1
Forum section: electronics / projects

author: TeslaPunk
author_rank: Newbie
timestamp: August 11, 2016, 11:08:01 pm
content: I have been looking for a "simple" amplifier circuit that can amplify a 0.5 Vp-p @ 10 MHz to 5 Vp-p. Seems simple enough but every BJT or Op Amp circuit I find and model in LTSpice shows little gain if not a loss at 10 Mhz. I am hoping to get away with a single active device, but even push pull circuits don't seem to get the job done. Any examples of such a circuit anyone can share; it would be appreciated (pictorial view attached).

author: StillTrying
author_rank: Super Contributor
timestamp: August 11, 2016, 11:42:00 pm
content: I don't know whether it would be any good in real-life.

author: Marco
author_rank: Super Contributor
timestamp: August 12, 2016, 01:25:47 am
content: You'd be running the LT1252 a bit outside it's datasheet max currents.How about LM6181?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: August 12, 2016, 03:03:21 am
content: Something like this maybe? (I only mention it because I have a jar full of these things, NOS.)

author: SethGI
author_rank: Regular Contributor
timestamp: August 12, 2016, 03:09:35 am
content: Check out Dave's vid on Op-Amps. That should have your answer...

author: ludzinc
author_rank: Unknown
timestamp: August 12, 2016, 03:56:12 am
content: Quote from: TeslaPunk on August 11, 2016, 11:08:01 pmX10 gain @ 10MHz means you need an amp with an open loop bandwidth of 100MHz minimum.Hard to get as op amp. Look for an MMIC.

author: awallin
author_rank: Frequent Contributor
timestamp: August 12, 2016, 05:18:47 am
content: some op-amps used in 10MHz distribution amplifiers that might work:MAX477AD8055ADA4899-1 (good distortion spec but slew-rate a bit low)LMH6702LMH6609

author: Someone
author_rank: Super Contributor
timestamp: August 12, 2016, 05:29:46 am
content: Quote from: ludzinc on August 12, 2016, 03:56:12 amVarious current feedback opamps will meet the requirement, not as unusual as they used to be.

author: GK
author_rank: Super Contributor
timestamp: August 12, 2016, 06:16:42 am
content: Op-amp open loop bandwidths generally span tens of Hz to tens of kHz and there are a gazillion VFAs with =>100MHz gain-bandwidth-product out there. What planet are you lot living on?

author: Marco
author_rank: Super Contributor
timestamp: August 12, 2016, 07:18:01 am
content: Oops, for some reason I was thinking for 5V amplitude AC instead of 5Vpp. Yeah at 5 Vpp there are tons of opamps which can do it, including the LT1252, 10 Vpp not so much (although the LM6181 should be able to do it).

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 12, 2016, 07:23:22 am
content: Quote from: ludzinc on August 12, 2016, 03:56:12 amcurrent buffer opamp like a THS3095 is heaven in this application, but their price range can be $10 a chip. they dont quite follow the BW=GBW/GAIN rule. for example the THS3095, its BW can be 100MHz whether the gain is 1 or or 5 or 10, you just need to change the feedback resistance Rf. the drawback of cfb opamp is they have higher input bias and offset compared to fet opamp and they require more juice from power supply and get heated in normal operation. there are fet/vfb opamp in those BW range at cheaper price i believe, like OPA690, OPA696, LM7121, LM7171, LM6171. some of them a way more than the 100MHz BW. the mentioned OPA is 500MHz GBW, but i suspect it will be more expensive. if you need cheaper, go for 100MHz GBW LM6171... ymmv.

author: w2aew
author_rank: Super Contributor
timestamp: August 12, 2016, 12:54:04 pm
content: Quote from: GK on August 12, 2016, 06:16:42 amI think he "meant" to say Unity Gain Bandwidth of 100MHz... ;-)

author: rstofer
author_rank: Super Contributor
timestamp: August 12, 2016, 03:32:21 pm
content: If you can't get enough bandwidth out of one op amp, cascade two of them. Set the gain of each to sqrt(10).

author: Cerebus
author_rank: Super Contributor
timestamp: August 12, 2016, 05:27:03 pm
content: No discrete solutions from anybody?You haven't been too clear what your full requirements are so I've made some assumptions, namely that you don't need DC coupling and don't care about relatively low frequencies. Here's my discrete BJT solution. It's not a totally finished design but it's close. It needs all the odd corners checked and obviously testing with real components.The schematic:C1 and C2 need adjusting to realistic values depending on your low frequency requirements.Noise performance is good, -97dB output noise for the stated conditions of 5V ptp in a 0.1 to 100MHz bandwidth. Not too shabby.Distortion isn't quite so good due to fairly small open loop gain. Here's the FFT for a full scale 10 MHz output.Closed loop frequency response isjustenough, no more.1kHz square wave response is very good, the slope on the top of the wave is just the LF rolloff.Gave me something to do this afternoon instead of sitting here feeling sorry for myself as I'm a bit off colour today.Editted to add:If anybody wants to play with the LTSpice file I uploaded you'll need to get the BJT models - I used the ones from Fairchild's site.

author: Yevhen
author_rank: Newbie
timestamp: August 31, 2018, 08:55:25 am
content: Thanks for this video, it's very helpful for the beginners like me.I built my amplifier based on two OPA694, about 2 x 20dB=40dB voltage gain.I need both DC and AC amplification, i.e. full bandwidth from DC to 100MHz is required.Is anybody suggest how to modify attached schematic in order to get rid of an offset?

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2018, 09:09:21 am
content: Hi,I would suggest that you have a look at the famous Jim Williams application note "High Speed Amplifier Techniques". Here you can find a 10Vpp amp too, using an op amp plus some discrete transistors.I made some, and they work nicely, even with a load drawing 1A.

author: Yevhen
author_rank: Newbie
timestamp: August 31, 2018, 09:38:32 am
content: Thank's Wolfgang. It's longest AppNote I ever saw.

author: David Hess
author_rank: Super Contributor
timestamp: August 31, 2018, 09:49:53 am
content: An AD8001 is suitable. An AD8055 or LT1192 would be less than 2dB down at 10 MHz so also work. These are all relatively inexpensive and available in both DIP and SOIC packages.Depending on your exact requirements, there are all kinds of discrete solutions.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2018, 10:58:40 am
content: You're welcome. I can also recommend his other app notes as well.They are jewels in a sea of either uninformative or buggy appnotes from others.Unfortunately Jim is no longer with us.