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Re: Need help to design a transimpedance amplifier
Hello to All,
This topic has a rather lengthy response indeed. I don't have a specific response, just a suggestion. I have a copy of a book that I have found very helpful in some of the designs I have don., You might consider getting a copy. Title: Photodiode Amplifiers Author: Jerald Graeme Publisher: McGraw Hill ISBN #: 0-07-024247-X It covers just about all aspects you will need in designing a good TIA. Good Luck with your design Pete |
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Probing phase
Howdy I am tying myself in knots trying to examine the buildup of phase in a relatively simple regulator circuit. ?I have uploaded Phase Analysis.zip to the files section. File darlington.asc contains two schematics, the second of which has been set up to examine phase and gain margin by breaking the feedback loop and inject AC small signal of 1. Run the simulation and plot -V(Vout_DD_stab)/V(Y) provides loop gain and phase. ?I read phase margin as the absolute difference between the reading for phase at the UGF and 0 or 180/-180 whichever is closer. ?In this case, I read -91 degrees for phase at UGF of 1.35Mhz and hence understand my phase margin is 89 degrees. (I understand that the -180 degree phase shift from the op amp inversion is omitted, presumably for simplicity.) [Incidentally, a few days ago LTspice produced the plot in Phase and Gain Margin - old.jpg. Note the differences in gain below about 10kHz. That plot was produced in an earlier schematic. I later encountered problems with the schematic no longer recognising .inc statements and hence refusing to work. I therefore produced a new schematic from scratch but updated LTspice at the same time. I've examined every inch of the schematic and there are no differences that I can see from old to new (all components and values are the same) and yet, while the UGF and phase margin results are the same, the gain plot below 10kHz is significantly different and seemingly 'less correct.' At this stage I can only (very gingerly) conclude that this resulted from the update to LTspice. ?Eek...] I now want to understand the contributors to the additional 91 degrees of phase shift and I am unsure of how best to probe the schematic when the loop is broken in this fashion. I have plotted several other traces. A. ?-V(vout_dd_stab)/V(OA_Out2) is intended to look at the phase shift from feedback network through to the output of the op amp. (Perhaps I have to change the numerator and denominator to see a plot of -180 degrees.) In a perfect world I would expect to see a flat line at 180 degrees. ? B. ?-V(vout_dd_stab)/V(Shift_Out2) is intended to add in the level shift network. As I would expect, judging from the lack of difference between this and the trace discussed above, the level shift is not contributing to phase shift.? C. ?-V(vout_dd_stab)/V(Driver_Out2) is intended to add in the driver transistor EF. Given the very limited difference between this trace and those above I conclude there is little contribution to phase shift from the driver transistor.? D. ?Presumably one would ordinarily conclude the balance of the (modelled) phase shift it coming from the pass transistor.? Am I 'probing' the schematic in correct fashion? Is there an easier way? I don't seem to be able to use a differential probe to identify phase shift between two points. For example, it would seem 'natural'?(on a Mac)?to be able to place the probe on Shift_Out2, left-click and hold while dragging it to OA_Out2 before releasing in order to examine any phase shift from the level shift network. ?Doing so, however, does not produce a flat phase line at 0 which one would conclude from examining the (lack of difference between) the first two traces discussed above (A and B). How can I directly plot the phase shift contribution of the pass transistor to test D above? ?Ordinarily I would not have thought it would contribute any significant phase shift.? Thanks in advance for any assistance Steve |
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Re: No XP?
Hello iamrogerholden
You wrote : "....and do I have to prevent LTspice updates to avoid an automatic XVII installation ?" I have tried to install LTspice XVII under Vista (I have not XP) : Nothing happens when I ran the installation program. LTspice IV and LTspice XVII installation programs are two different programs. So I think you have nothing to fear about. But only Linear Technology can answer you. Regards PhB |
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Re: No XP?
I am seriously concerned about the implications of this thread, I only use XP as it is compatible with all my other tools, does not randomly crash/freeze up and is no longer patched/botched by microsoft so is actually stable. I have no intention of installing later malware into my machines. I don't care about running the latest & greatest LTspice either but will the XT compatible IV continue to be available and do I have to prevent LTspice updates to avoid an automatic XVII installation ?
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Re: No XP?
Hello Gunoiar
You wrote : "No XP?..........and so on to go out on a whim of some marketing guy that prompts me to upgrade to his last contraption. Been there, done that! And now comes LTC (or shell I say ANALOG) with a new, 'improved" version of heir otherwise decent simulator." That don't seem to be very reasonable. Regards PhB |
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Re: Sub circuit heat dissipation not showing
The timestamps, as they appear in my mail, are positively amazing. I hope this gets corrected, eventually. Vlad ______________________ -- holding, among others: a universal analog/digital filter, block-level models for power electronics (and not only), math blocks with a more stream-lined approach, some digital ADC, DAC, (synchronous-)counter, JKflop, etc. |
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Re: PWL file in LTSPICE XVII not working while working in LT spice IV
Hello Andy,
He used by accident XVII86.exe instead of XVII64.exe. PWL is now working after he has used XVII64.exe. I wrote him a private email for this solution, because of the big delays of messages in the last days. Best regards, Helmut |
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Re: PWL file in LTSPICE XVII not working while working in LT spice IV
? ?"But when I try to install the 64 bit version, it installs the 32 bit. Don't know why?" You must have a 64-bit O.S. to run the 64-bit version.? Chances are your Windows is 32-bit. You could install Linux, as your cheapest way to get a 64-bit O.S. Andy |
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Re: PWL file in LTSPICE XVII not working while working in LT spice IV
alainstas141?wrote: ? ?"I think I 'm going to continue to use LT spice IV?" I think that is the best approach for now.? That's what I would do. Unless you have an absolute need to use LTspiceXVII's newer features, there is no NEED to change over to LTspiceXVII. ? ?"It's really a pity: this software seemed flawless up tyo now." The new program (LTspiceXVII) is a major re-write, so bugs should be expected (and excused for being there, IMHO).? LTspiceXVII hit the field rather quickly, without a very long period of testing; so I forgive it if it still has a few bugs that Mike hasn't yet fixed. FYI, Mike has also been spending time on the road, doing his LTspice seminars (on the other side of the planet from where he normally works).? He is a busy man.? But I am pretty sure there is only one of him, and he knows LTspice best. Andy |
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Re: No XP?
Craig wrote: ? ?" ? Maybe someone who's locked into XP could try dual-booting with Linux to run LTspice and let us know how it goes."I'm pretty sure at least two people here have already reported that LTspiceXVII does run in Linux with Wine emulating XP. I contend that Wine emulating XP is not 100% the same as Microsoft Windows XP, so to me at least, it's not surprising if it runs differently on an XP-emulator than on XP itself. Andy |
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Re: No XP?
?? Many Linux users dual-boot with Windows for the few Windows programs? without Linux equivalents (Intuit, I'm talking to you). Maybe someone who's locked into XP could try dual-booting with Linux to run LTspice and let us know how it goes. ?? Craig On Aug 7, 2016 5:23 PM, "Richard Damon richard@... [LTspice]" <LTspice@...> wrote:
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Re: No XP?
On 8/7/16 4:56 PM, ricksbmw@... [LTspice] wrote:
While I can't speak for Mike, I can say that often such restrictions are based on the tools used to build the program. Since XP is (past) EOL, many tools don't support generating new programs for it. Since LTSpiceVII is avail for 64 bits, it likely is using a newer tool than LTSpiceIV, and that might not support XP. -- Richard Damon |
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Re: No XP?
John Woodgate
¿ªÔÆÌåÓýSurely LTspice IV runs on XP and will continue to do so. As I understand it, the new graphics engine in XVII doesn't work on those legacy versions of Windows, which is hardly a surprise. ? With best wishes DESIGN IT IN! OOO ¨C Own Opinions Only J M Woodgate and Associates Rayleigh England ? Sylvae in aeternum manent. ? From: LTspice@... [mailto:LTspice@...]
Sent: Sunday, August 7, 2016 9:57 PM To: LTspice@... Subject: [LTspice] Re: No XP? ? ? It would seem reasonable for Mike to provide a short explanation of the technical reasons for not providing compatibility with XP (would it have been that costly?). |
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Re: No XP?
It would seem reasonable for Mike to provide a short explanation of the
technical reasons for not providing compatibility with XP (would it have
been that costly?).
A significant part of the world still runs XP because the economics of replacing perfectly good hardware with something that will support 7,8, or 10. It is not a trivial expense for a good part of the world, and detractors? don't seem to understand that. Rick |
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Re: Sub circuit heat dissipation not showing
Helmut wrote: ? ?"I have again problems with delayed or not delivered messages." It's not only your problem.? Yahoo is being hammered with problems this last week.? Those long delays are showing up all over. ? ?"Ctrl left mouse click on the plot formula in the waveform viewer.? ? ? LTspice will then show a small window with the average power." I think the confusion came up because LTspice displays a number for power dissipation, in the lower left corner of your LTspice screen, by just hovering the mouse pointer over a component and not clicking anything.? But that number is the power dissipation ONLY at time=0 into the simulation, and doesn't represent average power over a full cycle. The other confusion (which started this whole thread) is that LTspice doesn't show the power in the lower left corner, when the component is a subcircuit.? I guess that's just the way LTspice works; there is something about subckt models that makes that calculation not happen.? But for me, that number is not helpful anyway, even if it was there. Andy |
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Re: Current Dependent Voltage Source
Thanks to everyone who expertly explained how to accomplish this.? With all your help I was able to get my simulation to work?using the table of test data I collected.?? Thank you for helping me.? Sent from Yahoo Mail. On Thursday, August 4, 2016 8:31 AM, "Andy ai.egrps@... [LTspice]" wrote:
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" ? rmoreno.phone" asked how to enter a table of measured values for her/his CCVS.Vlad might have had the table descriptions a little bit confused with respect to your question, because I think the data you have is voltage/current values, not voltage/time values.? You wanted a controlled or dependent source, not an independent source. Using SPICE's built-in H element (current controlled voltage source or CCVS), LTspice *MIGHT* have the ability to accept a table of current/voltage values.? See the Help pages for E (VCVS) and G (VCCS) elements.? A table is listed as an option. ?"A look-up table is used to specify the transfer function." ?The same 'table' description is not listed for the F (CCCS) and H (CCVS) elements.? I am not sure if that was an omission on those Help pages, or if that option really doesn't exist for those two controlled sources.? The "LTwiki" () is where I usually go when I have questions about the Help pages.? Unfortunately, the LTwiki also doesn't show a table option for the CCVS.? That leads me to believe that you can't use a table with the standard CCVS element. But LTspice's B-elements can do that and much more. Here is from the Help page for B-elements: ? table(x,a,b,c,d,...) ??Interpolate a value for x based on a look up table given as a set of pairs of
points. Start with a Bv symbol, then right-click on "V=F(...)" and edit it.? I think (but could be wrong) it should look like this when you are done: V=Table( I(V4), 0mA, 0V, 1mA, 1mV, 2mA, 1.9mV, 3mA, 2.5mV ...) where I(V4) means the current measured through V4 (this is your controlling current), and the pairs that come next, are the (current, voltage) pairs that you measured. I have rarely used the Table() functions in LTspice, so please excuse my inexperience with them. Regards, Andy |
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Re: Need help to design a transimpedance amplifier
How come it took two days before my message were posted?
You look for an opamp, it's not the bias current you worry because you are only measuring 200nA lowest. Any opamp with bias current less than 10nA is plenty good. The most important thing you look for is input capacitance. Most of the opamps have over 5pF of input capacitance and that will increase the noise gain. You want to understand noise gain, read the explanation in my Excel file. I explain each and every component of the noise source and the relevant frequency range. I chose LTC6268 because the input capacitance is about 0.5pF. For your requirement, some BJT input opamp might be good enough, just look for low input capacitance. That said, you always see noise coupling into TIA circuits. I never saw a TIA circuit that dose not pick up all sort of noise.? All the noise calculation and the excel file I provided are ONLY for ideal theoretical noise limit. If you leave the bare circuit, you will see all the noise from around the surrounding. FYI, our contractor designed another TIA that has only a 1M feedback resistor and it pick up all sort of noise. We have to re-layout the board to put in the shield. A ground plane is an absolute MUST. The other reason is people have long trace at the -ve input. That will pickup noise every time. Layout is everything. This is beyond the scope of this forum. Circuit is always simple, it's the layout and shielding. You need to look at your layout, put in the shielding, then talk more about it. LTSpice is NOT the place to talk about this, go to some electronic forum and ask question. I feel I already way out of bound here already. You are only working with 50K feedback resistors. My circuit use 250M, and I designed with up to 2G resistors TIA circuits. Layout and shielding become the number one design. If you read my other post, 50K resistor will give you output range of 10mV to 5V( fit your 5V supply requirement). This is very easy signal to deal with. We deal with a lot lower signal successfully. |