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LM7171: Circuit Board Material vs Rise Time, Stability,Etc.(FR1 vs. FR4) and LT1166 Stability For Function Generator Output

Intellectual 615 points

Replies: 17

Views: 511

Part Number: LM7171

Hello!

I am designing a PCB with the LM7171 used in accordance with the Schematic in Figure 7 in the LT1166 datasheet (see below) and I am using it as the output amplifier in  a sine Square triangle (maximum freq. 5MHz) function generator (I am shooting for >50ns rise time on square but i don't think that effects the LM7171 for the purposes of this question) the out put would be a maximum of +-15Vpp.  I have two main questions, (a) would using the LM7171 be appropriate in the first place, and (b) would using FR1 vs FR4(for cost reasons) on the PCB affect The LM7171 in stability, rise time etc.?

Thanks for any help!

p.s. Here is the LT1166 datasheet((https://www.analog.com/media/en/technical-documentation/data-sheets/1166fa.pdf)).

  • Hi Fred,

    I have not fully understood what you want to do with the LM7171. Can you post a schematic?

    Concerning FR1 and FR4: If you run your application always at room temperature and at low humidity, FR1 will work. Many years ago I have designed HF-circuits running up to the GHz range with FR1 and it worked very well. But when it comes to multilayer boards with plated through holes, I would always use FR4, because you will get much more reliable boards with tighter tolerances. And if high temperatur changes are to be expected, FR4 (or better) is a must. Also remember that FR1 is very hygroscopic. Happily the price difference between FR1 and FR4 has beome much smaller in the last years.

    Kai

  • Well Fred, 

    That LT1166 is a pretty odd part to start from, Figure 7 is a current source output? 

    Anyway, most AWG output use a current feedback part, your speed needs are pretty modest but 15Vpp will probably need at least +/-10V supplies for CFA. 

    Lot's of choices driven by required load drive - are you using a 50ohm output. The latest (way overkill for you) is the THS3491, but there are approx. 100Mhz CFA as well to choose from. 

    Michael Steffes

  • In reply to kai klaas69:

    I will try to have a schematic done in a day or two if that is okay.  By the way, is it okay to attach an EAGLE schematic file to e2e?

  • In reply to Fred Doe:

    Unlikely we would be able to open an Eagle file, but a schematic snip might be enough - most e2e folks work in TINA. 

    Michael Steffes

  • In reply to Michael Steffes:

    Yes, I am using a 50 Ohm (ultimately BNC) output.

  • In reply to Michael Steffes:

    Would doing a screen shot be okay-- or is that what you are referring to with the "schematic snip"? *By the way, I do not have TINA, I only have EAGLE as my schematic drawing program.*

  • In reply to Fred Doe:

    Yes, that is what I meant. 

    Michael Steffes

  • In reply to Michael Steffes:

    Here is the schematic. I think it is readable, if it is not please let me know.  By the way, I think the LM334 is appropiate but if it is not, it is not a big deal to change it to a different current source/sink; also it is set to ~64 mA but also that would subject to change if that is not the appropriate value. 

  • In reply to Michael Steffes:

    Are there any CF amplifiers in a DIP with reasonable speed that could drive a 50 Ohm load like you had mentioned?

  • In reply to Fred Doe:

    Well DIPs were largely abandoned above 100MHz due to lead parasitics

    I really can't adapt your circuit to a more typical CFA design - and, what exactly are your design targets. 

    Michael Steffes

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