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'[EE] High Frequency Sawtooth generator'
2006\06\05@135137 by Edward Cooper

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face
Hi all

Anyone got any suggestions as to how to put together a 5MHz sawtooth  
generator, I'd really like something quite linear and adjustable if  
possible, can't see any simple chip solutions out there so looking  
for a bit of advice.

Its for playing with a FMCW radar module if anyone is interested

Cheers

Ed

2006\06\05@161754 by Gus S Calabrese

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What do you want to adjust ?   Frequency ?
DC offset ?  Amplitude ?

POD

Gus S Calabrese
Denver, CO
720 222 1309     303 908 7716 cell
I allow everything with  "spamcode2006"  in the subject or text to  
pass my spam filters


2006\06\05@180706 by Edward Cooper

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frequency

thanks

On 5 Jun 2006, at 21:17, Gus S Calabrese wrote:

{Quote hidden}

> --

2006\06\05@184216 by Marcel duchamp

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Edward Cooper wrote:
> frequency
>
> thanks

Check out Apnote 13 by Jim Williams of Linear Technology.  He details an
F-V converter that runs from 1 Hz to 30 MHz.  You would not need most of
the digital control circuitry he shows but the current-source driving a
capacitor with a high speed comparator would do most of the work for you.

2006\06\05@184250 by Jinx

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> possible, can't see any simple chip solutions out there so looking  
> for a bit of advice.

MAX038

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257

2006\06\05@190303 by Edward Cooper

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face
Would be ideal, if i could work out how to get hold of them.

Ed

On 5 Jun 2006, at 23:42, Jinx wrote:

>> possible, can't see any simple chip solutions out there so looking
>> for a bit of advice.
>
> MAX038
>
> http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257
>
> --

2006\06\05@191412 by Gus S Calabrese

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This product was manufactured for Maxim by an outside wafer foundry  
using a process that is no longer available. It is not recommended  
for new designs. For further information, contact us. The data sheet  
remains available for existing users.


On 2006-Jun 05, at 16:42hrs PM, Jinx wrote:

> possible, can't see any simple chip solutions out there so looking
> for a bit of advice.

MAX038

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257

2006\06\05@192146 by Gus S Calabrese

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I have one that I can send you
POD


On 2006-Jun 05, at 17:02hrs PM, Edward Cooper wrote:

Would be ideal, if i could work out how to get hold of them.

Ed

On 5 Jun 2006, at 23:42, Jinx wrote:

>> possible, can't see any simple chip solutions out there so looking
>> for a bit of advice.
>
> MAX038
>
> http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257
>
> --

2006\06\05@192945 by Gus S Calabrese

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Take a look at this URL
http://www.analog.com/en/content/0,2886,760%255F794%255F94528,00.html


Gus S Calabrese
Denver, CO
720 222 1309     303 908 7716 cell
I allow everything with  "spamcode2006"  in the subject or text to
pass my spam filters

2006\06\05@194302 by Jinx

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> > MAX038

> Would be ideal, if i could work out how to get hold of them.

Sorry, I had no idea they'd been obsoleted ;-((

RS UK still have them. At a price !!!

Maybe Maxim Integrated Products Ltd

http://www.applegate.co.uk/company/00/06/801.htm



2006\06\05@194907 by Jinx

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> Would be ideal, if i could work out how to get hold of them.

Ed, it seems Maxim are still sampling some forms of the MAX038.
I went part-way through the process and added them to my cart.
As they're EOL I think I might get a couple myself for future use

shop.maxim-ic.com/storefront/samplecart.do?partnumber=MAX038CPP%2B&r
ownum=2

2006\06\05@220928 by Rich Graziano

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A capacitor will charge at a linear rate if it is charged by a constant
current.  Typically, that is how a sweep (sawtooth)  generator is designed.
For a low frequency illustration put a capacitor in the feed back loop of an
op amp (Bipolar config.) and  apply a voltage to the inv input through a
resistor  and watch the liner slope on a scope.  It will be inverted from
the polarity of the input voltage because the R is in the inv input.  Of
course non-inv in is grounded. Discharge the cap and it will start again.
Polyester or polypropylene caps have a low leakage.  Best for this type of
application. So, you can design a constant current charge discharge at such
a frequency without too much difficulty.  5 MHz is not fast. If you like,
you can talk to me off-list about it and I can try to help you.  My hours
are often unpredictable.
Regards
Rich
{Original Message removed}

2006\06\05@222433 by kravnus wolf

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Cool chip there!

John

--- Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz> wrote:

{Quote hidden}

shop.maxim-ic.com/storefront/samplecart.do?partnumber=MAX038CPP%2B&r
> ownum=2
>
> --

2006\06\05@224921 by Jinx

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> Cool chip there!

> > the MAX038.

It's a pity they're out of production. I've used them off and
on (no pun intended) over the years, eg as variable clock
sources for micros, inductor testing, filter tuning etc. I note
that even the venerable ICL8038 is also not recommended
for new designs

2006\06\05@235150 by Vasile Surducan

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On 6/6/06, Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz> wrote:
> > > MAX038
>
> > Would be ideal, if i could work out how to get hold of them.
>
> Sorry, I had no idea they'd been obsoleted ;-((
>
> RS UK still have them. At a price !!!

MAX038 was an expensive copy of ICL8038, running at 5V and
with some minor improvements.

at 12MHz/$4 this is much better:
http://www.analog.com/en/prod/0,,770_843_AD9833%2C00.html

Vasile

2006\06\05@235939 by Vasile Surducan

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On 6/6/06, Jinx <joecolquittspamKILLspamclear.net.nz> wrote:
> > > MAX038
>
> > Would be ideal, if i could work out how to get hold of them.

www.exar.com/product.php?ProdNumber=XR8038A&areaID=

2006\06\06@011316 by kravnus wolf

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Any other replacement that we can use?

John

--- Jinx <.....joecolquittKILLspamspam.....clear.net.nz> wrote:

{Quote hidden}

> --

2006\06\06@015553 by Wouter van Ooijen

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>> MAX038
> Would be ideal, if i could work out how to get hold of them.

isn't Dallas/Maxim famous for their samples (as opposed to infamous for
buying mid-volume amounts of chips from them)?

otherwise http://www.voti.nl/shop/p/IC-MAX038-DIP.html

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\06\06@024236 by Vasile Surducan

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On 6/6/06, Wouter van Ooijen <EraseMEwouterspam_OUTspamTakeThisOuTvoti.nl> wrote:
> >> MAX038
> > Would be ideal, if i could work out how to get hold of them.
>
> isn't Dallas/Maxim famous for their samples (as opposed to infamous for
> buying mid-volume amounts of chips from them)?
>
> otherwise http://www.voti.nl/shop/p/IC-MAX038-DIP.html

Oh boy. are you sure the comma is in the right place ?
:)
Vasile

>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: http://www.voti.nl
> consultancy, development, PICmicro products
> docent Hogeschool van Utrecht: http://www.voti.nl/hvu
>
>
> -

2006\06\06@031932 by Wouter van Ooijen

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> Oh boy. are you sure the comma is in the right place ?

Yes. If you have a source for E 3.00 I'd love to buy some!

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\06\06@174020 by Peter

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On Mon, 5 Jun 2006, Edward Cooper wrote:

> Hi all
>
> Anyone got any suggestions as to how to put together a 5MHz sawtooth
> generator, I'd really like something quite linear and adjustable if possible,
> can't see any simple chip solutions out there so looking for a bit of advice.
>
> Its for playing with a FMCW radar module if anyone is interested

I have done this, almost for the same purpose. Many better opamps can
generate a triangular waveform at 5MHz with very good linearity using a
standard schematic. Use a small R so the C can be relatively large (this
requires an opamp with some power bandwidth). You probably want a
triangular waveform (not sawtooth) for FMCW. That is what I used. Even a
venerable uA733 can do this quite well. A more modern device would be
from National or Maxim, e.g.:

http://www.national.com/pf/LM/LMH6732.html

The app. notes are also worth reading, esp. OA-15, OA-30 and OA-31 . A
schematic for a sawtooth generator using a current controlled opamp can
be found in the LM3900 datasheet, among other places.

Note that it is dead easy to make one of these oscillate, the wiring
layout must be VHF at least. No flying pigtails here. By the way the
LMH6732 has almost unbelievable performance imho. 1nV/sqrt(Hz) at 100kHz
 and 3mA bias ?!

hope this helps,
Peter

2006\06\07@004749 by Vasile Surducan

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On 6/7/06, Peter <plpspamspam_OUTactcom.co.il> wrote:
{Quote hidden}

Peter, it looks like this one has a variable bandwith between 50-540MHz.
Have you tried to use it as a controlled LPF ? The guys from National
claimed 1.5GHz BWT at -3dB, did you check that ? I must order one...
BTW, it's too good for a 5MHz sawtooth...

thx,
Vasile


{Quote hidden}

> -

2006\06\07@013758 by kravnus wolf

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>
>
> Peter, it looks like this one has a variable
> bandwith between 50-540MHz.
> Have you tried to use it as a controlled LPF ? The
> guys from National
> claimed 1.5GHz BWT at -3dB, did you check that ? I
> must order one...
> BTW, it's too good for a 5MHz sawtooth...
>
> thx,
> Vasile
>
 I ordered it with the evaluation board! Too good to
be true!


John

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2006\06\07@162039 by Peter

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On Wed, 7 Jun 2006, Vasile Surducan wrote:

>> http://www.national.com/pf/LM/LMH6732.html
>
> Peter, it looks like this one has a variable bandwith between 50-540MHz.
> Have you tried to use it as a controlled LPF ? The guys from National
> claimed 1.5GHz BWT at -3dB, did you check that ? I must order one...
> BTW, it's too good for a 5MHz sawtooth...

I have not yet put my hands on one of them but it is on the list. I
wanted to suggest a different video speed opamp from Motorola but I
found this instead while looking for the datasheet. I like the very low
noise at HF-VHF. This could make a very nice IF amplifier and even a
front end. But I don't understand why the noise is much higher on the
(-) input.

Peter

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