generating sine wave

Is there any simple method to generate a sine wave of frequency 1MHZ by using LM324 op-amp/by using filters /by using oscillators (please mention the specifications and schematic diagrams). please reply me with in 24 hours(urgent).

Reply to
pinku
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Is there any simple method to generate a sine wave of frequency 1MHZ by using LM324 op-amp/by using filters /by using oscillators (please mention the specifications and schematic diagrams). please reply me with in 24 hours(urgent).

Reply to
pinku

Homework or business ?

1 MHz is a bit fast for an LM324 btw ! Would you like to consider another device ?

My hourly rate is $80 btw.

Graham

Reply to
Eeyore

"Eeyore" schreef in bericht news: snipped-for-privacy@REMOVETHIS.hotmail.com...

And payment term 24 hours ;)

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Reply to
Frank Bemelman

The answer is no, whch isn't going to help get your homework done.

If you look at the data sheet for the LM324

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and check out page 7, you will see that amplfier runs out of small signal gain at about 1MHz (top of page, left hand side) while the large signal output swing falls below 1V at 100kHz.

If your instructor was silly enough to specify an LM324 as the op amp to use for this job you've got an easy answer to the question. Otherwise you are going to have to start out by finding a faster amplifier.

How much distortion in the sine wave can you accept? What sort of amplitude do you need? Does the frequency have to be exactly 1MHz? If so, tell us what sort of range frequencies would count as "exact" -

+/-10Hz?

How stable do amplittude and frequency have to be?

In the meantime, googling on Wien bridge and phase-shift oscillators might give you some ideas.

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The circuit given above for the Wien bridge will produce a rather distorted sine wave - there are better versions of the Wien bridge, See Jim Williams Linear Technology application note AN43 on bridge circuits

- the first half of the application notes talks about Wheatstone bridges, but the second half gets onto Wien bridges.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

If you have around >12V supply a quick and dirty way of getting a sinewave in the low MHz-region is with a tuned cross-coupled long tail pair.

Vs-------------------+ | +--/////---+---/////--+ | --------L------- | | C | +----------||---------+ | | +--------/\\/\\/--------+ | RLoad | +---------, ,--------+ | \\/ | \\| /\\ |/ npn|--/\\/\\-' '-/\\/\\--|npn e/| R R |\\e | | +----------+-----------+ | \\ /Rtail \\ | 0v------------------+

L is the centre-tapped primary of a transformer and can be wound on about a 10mm ferrite toroid. Rload can be coupled directly as shown, or via a secondary winding.

L+C form a tuned circuit, resonant at 1MHz.

R should be about 10k.

The load on L+C is Rload and 2R in parallel (more or less).

Make the impedance of the C about 1/10 of the effective collector-collector load then calculate the value of L for resonance.

Assume a voltage across Rtail of about 1/3 to 1/2 of Vs. Start off with a tail current of around 1-2mA dc.

A bit quick and dirty, but it oscillates quite readily and is simple to breadboard.

--
Tony Williams.
Reply to
Tony Williams

at least that roll-off helps subdue harmonics.

Reply to
budgie

In message , dated Wed, 9 Aug 2006, pinku writes

We don't do 'urgent'. The LM324 isn't suitable for operation at 1 MHz. Choose a faster op-amp.

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Reply to
John Woodgate

"John Woodgate" a écrit dans le message de news: snipped-for-privacy@jmwa.demon.co.uk...

You're making the same mistake as Bill.

It sure can be done: (but I wont recommend this at all)

250p || .--------||----------------. | || | | | 100uH | |\\ | ___ | |\\ 6V >-|+\\ | 6V >-UUU-+-|+\\ ___ | >--+ L | >-+-----|___|-+-|-/ | .-|-/ | 1K | |/ | | |/ | | ___ | '------| '-|___|-+ | 1K | .-. .-. | | | | | | 4K7 | | 4K7 '-' '-' | | === === GND GND

For L, say Q>10 @ 1MHz.

To the OP: It'll oscillate but I won't say you why. One thing I can tell you though: don't show this to your professor (unless he has a good sense of humor). What happens if you exchange L and C. Why?

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Thanks,
Fred.
Reply to
Fred Bartoli

In message , dated Wed, 9 Aug

2006, Fred Bartoli writes

No, I'm being realistic. Using the LM324 at 1 MHz is the rankest of bad design.

This is with no DC supplies to the power pins? Evil!

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Reply to
John Woodgate

"John Woodgate" a écrit dans le message de news:2I7L+ snipped-for-privacy@jmwa.demon.co.uk...

Sure, but the design requirement to be completed with 24h always make me facetious.

Where did you see power pins?

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Fred.
Reply to
Fred Bartoli

I don't know that that's true. Given that you can make a Colpitts oscillator out of an emitter follower plus an impedance transforming network, it might be sort of fun to do the same with a 324. I bet you could make a 1 MHz oscillator out of one by using a pi network between the output and input. Not a very _good_ sine wave oscillator, but all you need is power gain, not voltage gain.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

The big problem with the 324 is its slew rate, (about 0.5V/us). At 1MHz, this would limit the output amplitude to about 160mV p-p for a sinusoidal waveform.

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T

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Reply to
TuT

In message , dated Wed, 9 Aug

2006, Fred Bartoli writes

They aren't shown, and no supply voltages are mentioned, but 6 V DC is applied to both op-amp + inputs. So I wondered if the power goes through parasitic diodes or something.

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Reply to
John Woodgate

One might as well go to a single transistor, which of course works fine for the purpose.

This is once again an example of someone stuck in low frequency mentality trying to extend it to radio frequencies. Time after time, we see people needing an oscillator at 1MHz or so, and want to know why their op-amp or function generator IC doesn't work very well up there. Of course, it's because they are hitting the top of the frequency range for the device, and while the range may include 1MHz, that doesn't mean the IC designer every intended good operation up there.

Yet, they are trained in op-amp and IC solutions, so they can't see that long before op-amps came along, such an oscillator would be made with a single active element, tubes in the past, a transistor in recent decades. The 324 is a stretch at 1MHz, but it's close to DC for building an LC oscillator with a single active element. It's all perspective.

Michael

Reply to
Michael Black

With an LM324, no. According to the data sheet:

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, At 1 MHZ, its gain is unity, so it will not oscillate. (well, maybe just a little, but it'd be a nightmare trying to get it stable.)

Sorry, Rich

Reply to
Rich Grise

It isn't a mistake - if the OP asked the question, he isn't in state to make any sense of your kind of answer. And he still won''t get more than the 160mV out=3Dput swing set by the 0.5V/usec slew rate as worked out by TuT - I haven't checked that calculation, but it looks to ba about right.

My guess is that it would still oscillate at the same frequency, because you'd still have a 180 degree phase shift bewteeen the voltage drop across L and C, not to mention the 180 degrees across the two op amps.

--=20 Bill Sloman, Nijmegen

Reply to
bill.sloman

If you want to use the LM324 you'll need a negative resistance from the parts bin.

Tim

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Reply to
Tim Williams

In article , TuT wrote: [....]

I haven't tried this but here's an idea to get around that.

Use only one output of the LM324 and make a Colpitts common collector oscillator by placing an impedance in the ground line of the package. IIRC the compenation of the LM324 controls the slew rate of the output vs the ground pin.

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Reply to
Ken Smith

"Ken Smith" a écrit dans le message de news:ebgn3d$a17$ snipped-for-privacy@blue.rahul.net...

Hehe... I thought about boostrapping the supplies, but this one is a nice weird idea.

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Thanks,
Fred.
Reply to
Fred Bartoli

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