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pfaisalbe
Explorer
Explorer
8,730 Views
Registered: ‎07-28-2010

CLIPPED SINEWAVE CLOCK

Hi

 

I have been using square wave output oscillator to feed FPGA . I have seen oscillators with clipped sinewave output. If I use those oscillators (replacing the square wave output oscillator),  Would it cause a problem ?

 

Based on my little knowledge , No need to be a square wave , as long as the frequency is maintained. When it is a clipped sine wave , I would think it has both positive and negative half.

 

Also ouput impedance of oscillator is specified as 10 Kohm // 10 pF. How this will affect ?

 

Here is the data sheet

 

http://docs-europe.electrocomponents.com/webdocs/0e32/0900766b80e32cf6.pdf

 

Thanks

 

Faisal

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11 Replies
eteam00
Professor
Professor
8,715 Views
Registered: ‎07-21-2009

I have been using square wave output oscillator to feed FPGA . I have seen oscillators with clipped sinewave output. If I use those oscillators (replacing the square wave output oscillator),  Would it cause a problem ?

For single-ended (not differential) signals such as this, faster edges mean less susceptibility to noise inducing input clock jitter.  If dv/dt is slow in or near the switching region, induced voltage noise will displace the clock edge -- in time -- in the FPGA.  In other words, induced signal noise would be manifested as clock jitter.

Also output impedance of oscillator is specified as 10 Kohm // 10 pF. How this will affect ?

No, this is the load impedance (the FPGA pin being driven by the oscillator), not the oscillator output driver impedance.

 

Big difference, Faisal.

 

I would tell you that FPGA LVCMOS25 input should be fine -- but I can't.

There is no VOH (output "high" voltage) spec in the datasheet, and I doubt that the output is open-drain or open-collector.

 

Out of curiosity...  how much does this little oscillator cost you, Faisal?

 

-- Bob Elkind

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pfaisalbe
Explorer
Explorer
8,709 Views
Registered: ‎07-28-2010

Thanks Bob,

 

Out of curiosity...  how much does this little oscillator cost you, Faisal?

 

2.28 pound sterling


I would tell you that FPGA LVCMOS25 input should be fine -- but I can't.

 

Does that mean output level of oscillator is  not compatible for SPARTAN 3



Here is another one from the same manufacturer . costs 1.87 pounds

 

http://docs-europe.electrocomponents.com/webdocs/0e32/0900766b80e32cf7.pdf

 

Another one  costs 64.28 pounds

 

http://docs-europe.electrocomponents.com/webdocs/0d6a/0900766b80d6a3f4.pdf

 

Kind Regards

 

Faisal

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eteam00
Professor
Professor
8,706 Views
Registered: ‎07-21-2009

I would tell you that FPGA LVCMOS25 input should be fine -- but I can't.

Does that mean output level of oscillator is  not compatible for SPARTAN 3

If I knew what the oscillator output levels (both LOW and HIGH), I might be able to answer you.

 

And it's not necessarily a matter of 'compatibility'.  You should feel confident about which input signal standard you pick for the oscillator input, right?

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
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drjohnsmith
Teacher
Teacher
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Registered: ‎07-09-2009

hi

 

had quick look at the data sheet link.

 

there seem to be two types of oscilator on the sheet, 5v and 2v8.

 

As it's an osilator, not a xtal, things are a little easier .

 

just slelect the same output voltage of the new oscialtor as the old one.

 

cliped sine wave,

    well some radio people seem to like them, 

 

 

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
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eteam00
Professor
Professor
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Registered: ‎07-21-2009

had quick look at the data sheet link.

just slelect the same output voltage of the new oscialtor as the old one.

Dr. John,

In your opinion, based on the device datasheet, what is the device output swing?

 

Faisal,  I suspect you would have better luck with the 'TW' part (not 'TV') with CMOS output.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
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pfaisalbe
Explorer
Explorer
8,643 Views
Registered: ‎07-28-2010

Thanks Bob,

 

Faisal,  I suspect you would have better luck with the 'TW' part (not 'TV') with CMOS output.

 

Sorry, I can't follow you.

 

From the datasheet ,output clock is of 0.8 (Vp-p) .This is not an acceptable  I/O standard for SPARTAN 3. Is that right ?

 

Please see the attached document.

 

Using Second oscillator with integrator (for CMOS output) , Would this work?

 

Regards

 

Faisal

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eteam00
Professor
Professor
8,630 Views
Registered: ‎07-21-2009

Faisal,  I suspect you would have better luck with the 'TW' part (not 'TV') with CMOS output.

Sorry, I can't follow you.

Taiten makes a similar part, with similar specs, with standard CMOS output levels.  This is the 'TW' part.  Check the Taiten website.

From the datasheet ,output clock is of 0.8 (Vp-p) .This is not an acceptable  I/O standard for SPARTAN 3. Is that right ?

Correct.

Using Second oscillator with integrator (for CMOS output) , Would this work?

Or just use an oscillator with CMOS output.  Pick the right part for the job, Faisal!

 

- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
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pfaisalbe
Explorer
Explorer
8,620 Views
Registered: ‎07-28-2010

Thanks Bob,

 

Taiten website is impressive. However a few of them are available from the UK reseller.

 

However here is one with HCMOS output.  Ouput voltage level seems ok to drive FPGA. But In SPARTAN 3 datasheet ,  HCMOS is not mentioned

 

http://www.farnell.com/datasheets/94305.pdf

 

Regards

 

Faisal

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eteam00
Professor
Professor
8,613 Views
Registered: ‎07-21-2009

Looks good, Faisal.

 

Don't be overly impressed by Taiten.  There are several suppliers of equivalent parts.

 

If you are a student, and you only need a few parts, sometimes a manufacturer or distributor will allow you a few free sample parts for evaluation purposes.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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rcingham
Teacher
Teacher
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Registered: ‎09-09-2010

Or just buy from RS!

------------------------------------------
"If it don't work in simulation, it won't work on the board."
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eteam00
Professor
Professor
2,956 Views
Registered: ‎07-21-2009

 


@rcingham wrote:
Or just buy from RS!

Faisal, he is just kidding you.

 

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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