Author Topic: Op Amp (uA741CN) Help  (Read 37206 times)

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Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #50 on: May 05, 2011, 11:39:04 pm »
Remember not to push the GBWP to the limit...
BTW: which is the situation about samples in your country? Don't TI, Analog, Linear and National send them?
i will figure out the GBWP limit thing, this is new to me. i believe something to be learnt.
thanx for reminding me about the sample program. i just filled the form. it seems successfull, but i dont know... we'll see.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline joelby

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Re: Op Amp (uA741CN) Help
« Reply #51 on: May 06, 2011, 01:58:15 am »
If you're just buffering or amplifying a fixed frequency signal, why not use an RF transistor as an amplifier instead of an op amp?
 

Offline allanw

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Re: Op Amp (uA741CN) Help
« Reply #52 on: May 06, 2011, 04:06:32 am »
Extra bandwidth isn't a big deal. You can always slow the op-amp down by putting a capacitor in parallel with the feedback resistor.

You should simulate extensively but sometimes it doesn't actually match up to real life.
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #53 on: May 06, 2011, 05:41:09 am »
If you're just buffering or amplifying a fixed frequency signal, why not use an RF transistor as an amplifier instead of an op amp?
buffering/amplifying non fixed signal shape and frequency, it could be arbitrary signal, the FG in question is Hantek 3x25 Arbitrary Function/Wave Generator.
i'd love to use transistor as well. but since my knowledge is very limited, a simple link(s) info on "transistor as a high frequency amplifier" could be very helpful.
and last time while looking for audio amp circuit, to be able to generate +ve to -ve signal (pure sine?), we need several setup and stages of transistors and have to deal with clipping/distortion at "near 0V" region.

thanx allanw for the advice. isnt an oscilloscope enough for that simulation? ie make the real circuit and debug?
ps: and i have this in mind... auto balancing bridge for impedance analyzer using the high speed op amp (i'm reading the agilent 5968-4506E.pdf ::))
« Last Edit: May 06, 2011, 05:54:41 am by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline allanw

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Re: Op Amp (uA741CN) Help
« Reply #54 on: May 06, 2011, 05:55:26 am »
Doing your own discrete design won't be trivial if you have such high specs (why do you think there's very few op-amps that have 7k slew rate and 2GHz GBW?)

Use findchips instead of ebay. The TI parts are available on Digikey but they're non-stock.

Also they're current-mode, which is different than traditional op-amp topologies. Since it's so fast, parasitics will cause it to oscillate easily unless you lay it out carefully. Even something like having a ground plane underneath the op-amp is discouraged because it adds too much capacitance at the input nodes to ground. So you'll also need to build your own board and do it right. There's plenty of readings online for this though, look up high-speed op amp layout.

For simulation: use LTspice. You should figure out the circuit before you actually build it.

Anyway, I don't think going from using the LM741 to the fastest current-mode op-amps available on the market is a very good transition. Maybe you should start with something in the middle.
« Last Edit: May 06, 2011, 06:01:46 am by allanw »
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #55 on: May 06, 2011, 07:19:31 am »
There's plenty of readings online for this though, look up high-speed op amp layout.
this is a helpful keyword, thanx. i have Dave's PCB pdf somewhere in my HDD. will be reading it.

Use findchips instead of ebay. The TI parts are available on Digikey but they're non-stock.
(why do you think there's very few op-amps that have 7k slew rate and 2GHz GBW?)
http://www.findchips.com/avail?part=high+slew+rate many parts, good! gotta download all the spec so to know whats the slew rate figure is. past few days, i was downloading bunch of datasheets just to find out the definition of high slew rate can be something from just a few hundred V/us, and high speed can be as little more than 10MHz. deleted many of the pdf so not to fuzzy my brain. only TI provides KV/us at GHz BW (but in the form of CFB opamp sigh). even LT or any other VFB cannot defeat.

For simulation: use LTspice. You should figure out the circuit before you actually build it.
i dedicated a new thread for this.

Anyway, I don't think going from using the LM741 to the fastest current-mode op-amps available on the market is a very good transition. Maybe you should start with something in the middle.
maybe i'm just heading to an evil in the dark.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline scrat

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Re: Op Amp (uA741CN) Help
« Reply #56 on: May 06, 2011, 08:40:37 am »
only TI provides KV/us at GHz BW (but in the form of CFB opamp sigh). even LT or any other VFB cannot defeat.

Using CFB and low value resistors is the way to go at the highest frequencies. Just think of what a few pF parasitic can do if in parallel with the high input impedance of a VFB opamp. The feedback input pin of a CFB opamp is ideally shorted to gnd, thus minimizing the R*C time constant at that node.

Anyway, I don't think going from using the LM741 to the fastest current-mode op-amps available on the market is a very good transition. Maybe you should start with something in the middle.
maybe i'm just heading to an evil in the dark.
I agree with allanw about the gradual moving towards higher frequencies. Even 10MHz at high gain can be a challenge...

One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man. - Elbert Hubbard
 

Offline joelby

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Re: Op Amp (uA741CN) Help
« Reply #57 on: May 07, 2011, 05:52:31 am »
If it's for a lab solution, you could see if Mini-Circuits have an amplifier module that suits your needs. They have all sorts of things that don't show up in Digikey etc. searches and can provide modules (metal boxes with BNC/SMA connectors) as well as components.
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #58 on: May 07, 2011, 07:13:50 am »
thanx joelby. 1st impression on the main page is they sell high speed products, i havent browse very detail yet. just looking for the chip (hi-speed amp), put in search box... BW 1-100MHz, gain 1-3, result none = "Please go Back and review / change your requirement or Contact Us.", i havent put the slew rate requirement yet. thanx for the link anyway. and to scrat for the advice.

If it's for a lab solution, you could see if Mini-Circuits have an amplifier module that suits your needs. They have all sorts of things that don't show up in Digikey etc. searches and can provide modules (metal boxes with BNC/SMA connectors) as well as components.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline joelby

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Re: Op Amp (uA741CN) Help
« Reply #59 on: May 07, 2011, 07:18:31 am »
They sell pretty much everything.

Try not specifying a maximum gain. Perhaps amplifiers with less than 3dB gain aren't very popular!
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #60 on: May 07, 2011, 07:43:38 am »
now i see they sell very strange amplifier (picture). it is from my 100MHz BW amplifier search (i didnt specify the gain).
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline joelby

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Re: Op Amp (uA741CN) Help
« Reply #61 on: May 07, 2011, 08:51:34 am »
Could be good! They're usually very easy to use, and you can set gain through the bias current/voltage.
 

Offline Wim_L

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Re: Op Amp (uA741CN) Help
« Reply #62 on: May 07, 2011, 03:06:58 pm »
Those cross-shaped packages are fairly common for high frequency components.
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #63 on: May 07, 2011, 03:58:17 pm »
some sort of darlington arrangement? cant we just build using its equivalent circuit? (npn transistors)
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Online Zero999

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Re: Op Amp (uA741CN) Help
« Reply #64 on: May 07, 2011, 04:59:50 pm »
It certainly doesn't look like anything new, as you say, just a Darlington pair with some biasing resistors.
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #65 on: May 07, 2011, 06:11:14 pm »
i certainly need to go back in time. all this hi-tech stuff hi-tech "hot" opamp blinding my eyes :(
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline saturation

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Re: Op Amp (uA741CN) Help
« Reply #66 on: May 08, 2011, 04:40:30 pm »
Hiya mecha,

Well yes, the device you linked is just a darlington but the main reason for using the op amp voltage follower is megaohm input impedance and low output impedance.  So effectively, it doesn't load the Hantek.

The darlington RF amp you linked has an input impedance of 50 ohms, which is fine too.  But for isolating the 3x25 I prefer the voltage follower.


i certainly need to go back in time. all this hi-tech stuff hi-tech "hot" opamp blinding my eyes :(

Best Wishes,

 Saturation
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #67 on: May 08, 2011, 05:50:04 pm »
Hiya mecha...
hi. yup, alot to catch up. even this weird looking darlington turned out to be a norm. thanx for your advice about the impedance. have you look at the earlier posts? i found the THS3062/1, THS3202/1, THS3095/1 (suggested earlier). those are candidates for hi-speed hi-slew amplifier. maybe you can look into it better than i can. unfortunately, i've made an order before completing my lesson here. THS3062 & 3202 from free sample ti program. 3095 bought from ebay (with other stuffs combined), am waiting here...

ps: where have you been?! ;)
« Last Edit: May 08, 2011, 05:52:51 pm by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #68 on: May 25, 2011, 10:30:16 pm »
not so bad for a one night dead bug soldering. i was scared, but this one seems easy, maybe just because i dont have a spectrum analyzer :P
here the pictures of a working but "not yet" optimized 100MHz, G=5 CFB THS3095 TI Operational Amplifier.
thanx to all people who gave encouragement, esp credit to allanw for suggesting simulation. the design is "sim approved" before the opamp arrived!
cheers :)


from ths3095 to uA741... i hear them dancing!
ths3095: "hi 741. i respect you as the great ancestor. i hope you will be peace in the afterlife"
uA741: "hi 3095. i respect you for your speed and ease of use. serve your 'makers' well"

Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline saturation

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Re: Op Amp (uA741CN) Help
« Reply #69 on: May 25, 2011, 11:54:07 pm »
Awesome work mecha, will review this; its looks fantastic.  I was away on holiday, I think I posted a bit on another thread.  Sorry I missed this post, it was the culmination of all your op amp inquiries!

Hiya mecha...
hi. yup, alot to catch up. even this weird looking darlington turned out to be a norm. thanx for your advice about the impedance. have you look at the earlier posts? i found the THS3062/1, THS3202/1, THS3095/1 (suggested earlier). those are candidates for hi-speed hi-slew amplifier. maybe you can look into it better than i can. unfortunately, i've made an order before completing my lesson here. THS3062 & 3202 from free sample ti program. 3095 bought from ebay (with other stuffs combined), am waiting here...

ps: where have you been?! ;)

Best Wishes,

 Saturation
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #70 on: May 26, 2011, 06:04:59 am »
err, i think there's mistake in the schematic, the PD pin should be higher or floated compared to Vref (grounded). pls take note and read datasheet carefully if you are into it. just got back from work after rushing in the morning after posting this quick report. still havent claim my sleep yet. until then.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline qinaan

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Re: Op Amp (uA741CN) Help
« Reply #71 on: December 21, 2011, 12:16:49 pm »
Mech Can u fwd me the schematic of THS3091 based simple amplifier which can boost up signals for Hantek DDS-3X25 function generator from 1 Hz to 25 MHz. thanks
 

Offline MechatrommerTopic starter

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Re: Op Amp (uA741CN) Help
« Reply #72 on: December 21, 2011, 02:11:43 pm »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 


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