Recommend me an Op-Amp - Page 1
Forum section: electronics / beginners

author: wexeteme
author_rank: Contributor
timestamp: April 28, 2015, 08:06:57 pm
content: Hello EEVBlog,I am searching for some some op-amp that fulfills the following conditions:-I plan of using it at generating high freq oscillator-producing up to 10 MHz output signal-reasonable pricePlease refer me to some op-amp that is at last close to what I need.Thanks!

author: c4757p
author_rank: Super Contributor
timestamp: April 28, 2015, 08:13:09 pm
content: Well, you need one with a bandwidth significantly higher than the frequency you're generating. Say, 100MHz or so.There are alotof opamps in that range. Have you tried a parametric search?

author: jlmoon
author_rank: Unknown
timestamp: April 28, 2015, 08:26:44 pm
content: LM6181, old but still pretty fast and decent output drive... for starters

author: wexeteme
author_rank: Contributor
timestamp: April 28, 2015, 09:02:08 pm
content: LM6181 seems good but it looks like it isnt single supply one ...

author: Zero999
author_rank: Super Contributor
timestamp: April 28, 2015, 10:30:29 pm
content: Are you sure it's an op-amp you want?Why do you need a single supply op-amp for an oscillator?

author: wexeteme
author_rank: Contributor
timestamp: April 28, 2015, 10:47:14 pm
content: well comparator, I guess ?

author: c4757p
author_rank: Super Contributor
timestamp: April 28, 2015, 10:49:15 pm
content: Quote from: wexeteme on April 28, 2015, 10:47:14 pmWhat kind of oscillator are you looking to make? When you said you wanted an op amp, I imagined some sort of RC sinusoidal oscillator, but comparators usually are used to make relaxation oscillators.Totallydifferent kinds of circuits.I probably wouldn't use a comparator to make an oscillator at 10 MHz. Most are fairly slow, fast ones are very expensive, and a relaxation oscillator that fast will be jittery.Can you use a crystal oscillator?

author: wexeteme
author_rank: Contributor
timestamp: April 28, 2015, 10:52:30 pm
content: well I was thinking of that as well, you think that will come as cheaper and more efficient way to do it ?

author: opty
author_rank: Regular Contributor
timestamp: April 28, 2015, 10:53:04 pm
content: Maybe have a look AD8055 ?All opamps are single supply..., just need some bias.

author: free_electron
author_rank: Super Contributor
timestamp: April 28, 2015, 11:14:59 pm
content: Quote from: wexeteme on April 28, 2015, 09:02:08 pmall opamps are single supply. i dare you to find me one that really needs two ...

author: wexeteme
author_rank: Contributor
timestamp: April 28, 2015, 11:33:12 pm
content: okej, so for example, lets take ua741, how do I get it working on a single supply ?I got this circuitand its not oscillating ...why is that ? how can I fix it ?

author: Sirius631
author_rank: Contributor
timestamp: April 29, 2015, 04:43:11 am
content: That doesn't look like an oscillator to me. Maybe a low pass filter?When in college, many moons ago, we built lab oscillators out of Wein bridge and op amp. Wein bridge is RC network combining low-pass and high-pass filters into a tuned circuit with gain of 1/3. Put it through op amp circuit of gain 3 and feed output back to Wein bridge input and it oscillates. You need 2 caps of the same value and 2 resistors of the same value.You can look up the frequency formula. I'm rolling over and going back to sleep.

author: c4757p
author_rank: Super Contributor
timestamp: April 29, 2015, 05:06:32 am
content: Quote from: wexeteme on April 28, 2015, 11:33:12 pmWhat these circuits call "ground" is really just the point halfway between the op amp's supplies. You moved the supplies, but not the "ground" reference point. Move the reference too - use a voltage divider between V+ and ground instead of running your resistor directly to ground.

author: mtdoc
author_rank: Super Contributor
timestamp: April 29, 2015, 05:28:13 am
content: What he said. SeeVirtual GroundandHERE

author: Zero999
author_rank: Super Contributor
timestamp: April 29, 2015, 11:10:57 am
content: Quote from: Sirius631 on April 29, 2015, 04:43:11 amIt's an attempt at a Schmitt trigger oscillator.Quote from: wexeteme on April 28, 2015, 11:33:12 pmConnect a 1k resistor between pin 3 and +5V.5V is a bit on the low side for the 741. It may not work.And an op-amp is a bad choice here. You need a comparator but why bother when Schmitt trigger ICs are available?Use the 74HC14 which should be able to oscillate at 10MHz with no problems.