Hello Frex,
thanks for your fast response, and yes I know about the LT1088, it's obsolete for a long time, although an FAE has tried to tell me, that Linear Technology never did quit production of chips.
However, at the moment I have to handle some other urgent problems, but when everything is
silent again I would like to contact you again for sending over a PCB. By the way, I have got an old HP3400A TRMS-Multimeter for a reasonable price, that works pretty fine. "The holy gral" of TRMS-measurerment. ;-)
Kind regards,
Michael
thanks for your fast response, and yes I know about the LT1088, it's obsolete for a long time, although an FAE has tried to tell me, that Linear Technology never did quit production of chips.
However, at the moment I have to handle some other urgent problems, but when everything is
silent again I would like to contact you again for sending over a PCB. By the way, I have got an old HP3400A TRMS-Multimeter for a reasonable price, that works pretty fine. "The holy gral" of TRMS-measurerment. ;-)
Kind regards,
Michael
Hello,
The ERMSDCv1 is greatly inspired from LT's applications notes about LT1088.
I had also bought some time ago a thermal RMS voltmeter ( the HP3403A,
same as 3400A with digital readout) and i was very dissapointed by both..
The measurement dynamic of thermal voltmeters is very low and you need to play often with ranges (non-linearity at low-level).
It's because of this that i have build another design (ERMSDCV2) using the newer LTC1968 IC that work much better than LT1088 in it's bandwidth.
Today, LT1088 can only be a good choice if you need measurement bandwidth beyond 1MHz.
Regards.
Frex
The ERMSDCv1 is greatly inspired from LT's applications notes about LT1088.
I had also bought some time ago a thermal RMS voltmeter ( the HP3403A,
same as 3400A with digital readout) and i was very dissapointed by both..
The measurement dynamic of thermal voltmeters is very low and you need to play often with ranges (non-linearity at low-level).
It's because of this that i have build another design (ERMSDCV2) using the newer LTC1968 IC that work much better than LT1088 in it's bandwidth.
Today, LT1088 can only be a good choice if you need measurement bandwidth beyond 1MHz.
Regards.
Frex
Hi, Frex.
First excuse me for my bad english. Congratulations for your wonderful device.
I have a question. In ERMSDCV2.3 the levels a clip indicator are +2V / -2V. This corresponds to 2Vpk (4Vpp, 1.41Vrms - AC sinusoidal). At this level after attenuator (R68-1K / R75-549R) on an input LTC1968 enter signal 0.705Vpk (1.41Vpp, 501mVrms). On the schematic it's labeled: max 1Vpp (353mVrms). What do you mean?. In ERMSDCV2 design clip levels are +0.5V / -0.5V (on input LTC1968: 0.5Vpk or 1Vpp).
I want to ask you about something else. The datasheet (LTC1968) says: "Differential input range is 1VPEAK". In AC 1Vpeak(Vpk) = 2Vpp. Does this mean that the input IN1 (LTC1968) I can apply a 1Vpk(2Vpp) if IN2 is GND? Or in this case the error is increased? Thank you in advance !
Best regards
Ivan
First excuse me for my bad english. Congratulations for your wonderful device.
I have a question. In ERMSDCV2.3 the levels a clip indicator are +2V / -2V. This corresponds to 2Vpk (4Vpp, 1.41Vrms - AC sinusoidal). At this level after attenuator (R68-1K / R75-549R) on an input LTC1968 enter signal 0.705Vpk (1.41Vpp, 501mVrms). On the schematic it's labeled: max 1Vpp (353mVrms). What do you mean?. In ERMSDCV2 design clip levels are +0.5V / -0.5V (on input LTC1968: 0.5Vpk or 1Vpp).
I want to ask you about something else. The datasheet (LTC1968) says: "Differential input range is 1VPEAK". In AC 1Vpeak(Vpk) = 2Vpp. Does this mean that the input IN1 (LTC1968) I can apply a 1Vpk(2Vpp) if IN2 is GND? Or in this case the error is increased? Thank you in advance !
Best regards
Ivan
Greetings Frex !
Thanks again for replying to a post of mine, considering a cheap way to use a voltmeter to read millivolts. That is what led me to this post. I have to say that I'm only JUST savvy enough concerning electronics, to be able to appreciate your knowledge and talent. You have a great talent for presenting your projects on this forum as well. When you get everything together on the project presented, I would be very interested in getting in on any PCB deal you come up with. I'll try to keep up with this post for that reason, and for the opportunity to learn more. I wish you, and all posting here, the utmost in success with ALL of your projects. Hopefully, some will "rub off" on me as well.
Sincerely, tonequester.
Thanks again for replying to a post of mine, considering a cheap way to use a voltmeter to read millivolts. That is what led me to this post. I have to say that I'm only JUST savvy enough concerning electronics, to be able to appreciate your knowledge and talent. You have a great talent for presenting your projects on this forum as well. When you get everything together on the project presented, I would be very interested in getting in on any PCB deal you come up with. I'll try to keep up with this post for that reason, and for the opportunity to learn more. I wish you, and all posting here, the utmost in success with ALL of your projects. Hopefully, some will "rub off" on me as well.
Sincerely, tonequester.
Hello,
Ivan,
For the overload detecting level of +/-2V, you have +/- 708mV at the LTC1968 inputs.
No matter if it is AC or DC level, both can overload the IC.
The IC is given to +/-1Vpeak max for a 1% accuracy.
But if you want maintain better accuracy, you need to slightly below this level in any conditions.
So, if the overload level indicator start to blink, you must be careful about precision. Despite that, in some case (sine wave: low CF signal) you can apply higher level signal without concern.
Tonequester,
Thank you very much, and welcome to DIY electronic world.
Frex
Ivan,
For the overload detecting level of +/-2V, you have +/- 708mV at the LTC1968 inputs.
No matter if it is AC or DC level, both can overload the IC.
The IC is given to +/-1Vpeak max for a 1% accuracy.
But if you want maintain better accuracy, you need to slightly below this level in any conditions.
So, if the overload level indicator start to blink, you must be careful about precision. Despite that, in some case (sine wave: low CF signal) you can apply higher level signal without concern.
Tonequester,
Thank you very much, and welcome to DIY electronic world.
Frex
Group pcb buy
Greetings Frex, tonequester here.
I hate to be a bother, but I have never dealt with Euros before. I had to look up the symbol to make sure, that was what you were asking 30 of, for the group pcb buy. can you tell me if currency is exchanged automatically when using pay pal(I've never used it before), or if I need to get a current quote on how many dollars, 30 Euros are worth. Again, I'm sorry to bother, but I'm new to Internet purchasing, as well as forums. Thanks in advance, if you or anybody else can help me out here. tonequester out.
Greetings Frex, tonequester here.
I hate to be a bother, but I have never dealt with Euros before. I had to look up the symbol to make sure, that was what you were asking 30 of, for the group pcb buy. can you tell me if currency is exchanged automatically when using pay pal(I've never used it before), or if I need to get a current quote on how many dollars, 30 Euros are worth. Again, I'm sorry to bother, but I'm new to Internet purchasing, as well as forums. Thanks in advance, if you or anybody else can help me out here. tonequester out.
30 Euros = $ 40.06
When you pay over paypal, you will specify currency, in this case Euro, € here is the symbol, and the amount 30. Paypal gives you an option to use their conversion or to use currency conversion from your bank. My advice would be to use currency conversion from your bank, since you will always get better rate. Regardless of which one you choose there will be a minimal difference with such a small amount. Type email address for Frex and send. It cannot be simpler.
You will be charged in US $ and Frex will receive payment in €.
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Greetings AR2 and thanks. OL' tonequester really appreciates your giving me the "low down" on this matter. I"m pretty far behind the times, but trying hard to catch up. I just don't have any friends or relatives who I can go to for such information. It may be hard to believe but some of my bunch rely on ME, to help them with computers and such ! Often they are sh__ out of luck. I just joined PC Help forum tonight. I'm hoping that I can bother those guys on some of these matters that don't really pertain to electronics/audio/music. One things for sure. I can't get any WORSE OFF, than I am right now ! Actually, I'm better off for joining this forum, and meeting guys like you.
Thanks again, and glad to "meet" you here. tonequester out.
Thanks again, and glad to "meet" you here. tonequester out.
I am glad to help. This is certainly an outstanding forum. You will like it here.
Best
found a home !
Greetings AR2. I just had to say that I've quit a couple of well known forums due to huge ego's and bad manners, and sometimes downright bullying. Folks here seem to be really sociable, and willing to help even a half wit like me. I hope that I can one day, repay many favors received already.
Regards, tonequester.
Greetings AR2. I just had to say that I've quit a couple of well known forums due to huge ego's and bad manners, and sometimes downright bullying. Folks here seem to be really sociable, and willing to help even a half wit like me. I hope that I can one day, repay many favors received already.
Regards, tonequester.
I know it's an old thread, but i'm trying to make a LNA based on this one. Can anyone tell me in general terms:
-the idea behind the op amp selection in the different stages (is low noise the only important thing?)
-what are the main main requisites for the passives components?
-the reason for filters orders and frequencies.
-is important the filter position? I mean the high pass before the low pass
kind of new to all this low noise/presicion stuff.... thanks in advance!
-the idea behind the op amp selection in the different stages (is low noise the only important thing?)
-what are the main main requisites for the passives components?
-the reason for filters orders and frequencies.
-is important the filter position? I mean the high pass before the low pass
kind of new to all this low noise/presicion stuff.... thanks in advance!
I do precision circuit design for a living. Precision design really takes you back to the fundamentals. It's not a knowledge base I would easily be able to distill into a forum post.
I suggest getting a copy of Walt Jung's "Op Amp Applications Handbook". I have it in book from, but I think it's available for download on ADI's website. After reading the chapter on precision circuit design, you'll start to wonder how anything works at all... It's not really a textbook per se. It reads more like an application note, so it's a bit more accessible to the hobbyist.
In precision design, you can safely assume that the components were chosen carefully.
~Tom
I suggest getting a copy of Walt Jung's "Op Amp Applications Handbook". I have it in book from, but I think it's available for download on ADI's website. After reading the chapter on precision circuit design, you'll start to wonder how anything works at all...
It's not really a textbook per se. It reads more like an application note, so it's a bit more accessible to the hobbyist.In precision design, you can safely assume that the components were chosen carefully.
~Tom
I'm building a similar circuit to measure a voltage regulator with a very low noise floor. For the opamps, you want low offset voltage, low noise, and reasonable gain-bandwidth. Put as much gain up front as you can. I plan to use two stages with 100x gain rather than the two stages of 31x followed by one 10x gain stage that the OP uses. Modern opamps have enough open loop gain to deliver decent bandwidth even at high amplification.
The OPA211 would be a good opamp candidate. As would the AD797.
~Tom
The OPA211 would be a good opamp candidate. As would the AD797.
~Tom
Hello all,
I agree with Tom. Building and optimizing low noise high-gain block will require good design skill. Reading this book will be a good starting point.
You must know too, that bare circuit board of the design subject of this thread (ERMSDCV2) is available for sale from me. Building projects is also a very good mean to learn !
Regards.
Frex
I agree with Tom. Building and optimizing low noise high-gain block will require good design skill. Reading this book will be a good starting point.
You must know too, that bare circuit board of the design subject of this thread (ERMSDCV2) is available for sale from me. Building projects is also a very good mean to learn !
Regards.
Frex
Hi Tom! I have an LME49990 (sampled from TI a while back) with 0.9 nV/√Hz (typ) and a Gain Bandwith Product of 110 Mhz. If I understand correct with one stage with a gain of 1000 I would have a bandwith of 110 kHz, a little bit more than the 100kHz I need for the LNA. Is that correct?
That would be great! Unfortunately, I live in Argentina (as my bad english clearly shows....) recent changes in import policies have made buying online almost imposible, unless you are an official importer working with a customs broker...
Richard, You know it is bad Kharma to talk about someting and not
do "show and tell", complete with board shots and how what each piece
does.
If we are nice and buy you a beer can we send you some ICs and OpAmps
to check out and test for us DiYer who don't have access to such hi end
M&T gear. What did you get it for? From where did you dig it up.
Cheers from the pond's same side.
