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Re: Question: any built-in function that returns the type of analysis being run?
analogspiceman,
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Thank you for your very helpful response. I suspect I will be able to use your information to solve my present issue. Best wishes, Robert --- In LTspice@..., "analogspiceman" <analogspiceman@...> wrote:
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Re: Question: any built-in function that returns the type of analysis being run?
Helmut,
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Thank you for your kind response. I will try this. I suspect it will solve my issue. Robert --- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
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Re: How to find Qpoint of an MOSFET in LT spice
On 9/7/2012 10:52 AM, dang quoc bao wrote:
Two good places to find help are: 1. Your textbook for the course you are taking. 2. A Google search using the phrase "MOSFET bias circuit". Howard |
Re: Question: any built-in function that returns the type of analysis being run?
--- In LTspice@..., "RobertS" <rstevescott@...> wrote:
But I am wondering where I might find the exact syntax forThis and other useful LTspice features not in the Help file are documented over on the LTwiki: Specifically for dual value resistors: |
Re: Question: any built-in function that returns the type of analysis being run?
--- In LTspice@..., "RobertS" <rstevescott@...> wrote:
Hello Robert, Simply replace the text 1k with 1k ac=100k. You can also place the ac=100k in an another attribute line. Therefore press "Ctrl" and right mouse click on the resistor to get the dialog window for all attributes. Value: 1k You could either change it to Value: 1k ac=10k or Value: 1k SpiceLine: ac=10k OK Best regards, Helmut
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Re: Question: any built-in function that returns the type of analysis being run?
Helmut,
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Thank you for your generous response. Your answer may well solve my problem. But I am wondering where I might find the exact syntax for defining different AC and transient values for a resistor. Could you point me in the right direction for such documentation? I don't seem to see it in the scad3.pdf file. Thanks --- In LTspice@..., "helmutsennewald" <helmutsennewald@...> wrote:
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Re: Question: any built-in function that returns the type of analysis being run?
--- In LTspice@..., Helmut Sennewald wrote:
I only know of the resistor which allows a different value in theI think I know what the original poster was getting at. He would like to switch models based on the type of analysis. For example, one might try to make a switched mode power supply that used an averaged model for an .ac analysis and a fully switched model for a .tran analysis. Perhaps this is a bad example because it can't easily be done just at the control IC level, but would require modifying the power stage as well. Anyway, there are other perhaps more effective ways to do this by switching between using a digital or continuous duty cycle control node (0<d<1). There are examples of this technique in our files section. In any case, one could use two analysis dependent resistors to make a SPDT switch to chose between two circuit models. Maybe an example where this would make more sense might be for a transformer winding model, which could switch between a Laplace version for .ac and a lumped approximation for .tran. -- a.s. |
Re: LT1016,
On 9/7/2012 7:08 PM, Malcolm Smith wrote:
Even though "Analog Circuit Design" Edited by Bob Dobkin and Jim Williams was published in 2011 the Publisher's Note in the book says: "This book was compiled from Linear Technology Corporation's original Application Notes. These Application Notes have been re-named as chapters for the purpose of this book." A cross reference in the book shows Chapter 34 "A seven-nanosecond comparator for single supply operation" is Application Note 72. Howard
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Re: Question: any built-in function that returns the type of analysis being run?
--- In LTspice@..., "RobertS" <rstevescott@...> wrote:
Hello, I only know of the resistor which allows a different value in the AC simulation. Instead of a value of 1kOhm in all types of simulation, 1k you can have a a different value in the AC-simulation. 1k ac=10k Best regards, Helmut |
Re: Foldback Simulation
--- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
Hello, The foldback characteristic is defined by the resistors R7 and R4. If the output voltage is low, the Ube of Q2 will become higher due to the extra current via R7. Thus less voltage drop on R1 will be necessary to make Q2 active (Ube>0.7V). Best regards, Helmut |
Re: SingleStage common emitter amplifier
Right you are. I disconnected the output capacitor and indeed currentThat's one of the great things about LTspice. You can SEE that the transistor's current goes to zero, even without disconnecting the output capacitor. Just hover the mouse over the collector pin until it turns into the ammeter icon, click, and see the collector current waveform. On a workbench we tend to think only of voltages (because they are easy to look at), but LTspice lets us look at things like currents just as easily. Andy |
Re: Foldback Simulation
--- In LTspice@..., "vittorio pomo" <VITTORIO_POMO@...> wrote:
Hello Vittorio, The extra V-source and the diode are the load. I start with a voltage higher than the unloaded output voltage. The diode is reversed bias in this case and thus the current is zero. When the test voltage source is below the unloaded regulator's output voltage, the diode becomes conducted and quickly the maximum current will flow. When I further decrease the voltage, the current will be reduced due to foldback. If the load is at 0V, the current will be at its minimum. When I plot V(out), "time" will be on the x-axis. Now I change the x-axis from "time" to "I(VL)" to get this standard plot showing the foldback characteristic. I just discovered that I only have to sweep VL from 15V to 0V. See my latest circuit. Files > Examples > Educational > foldback_simulation.zip Best regards, Helmut |
Re: SingleStage common emitter amplifier
rainbowsally
Andy wrote:
rainbowsally wrote:Right you are. I disconnected the output capacitor and indeed current goes to zero in the collector resistor.No. Only saturating.If you look again, there is more than just saturation going on. It And how this applies to ltspice (for those overly concerned about topic enforcement) is that you CAN do this without cutting traces on circuit boards with a razor blade but simply deleting a wire in our ltspice program. :-) The file being discussed is (I got it again, yes, a single transistor). racproj.asc in the files temp folder. Yup.But the distortion waveformI think the main reason for that asymmetry is C2 discharging, at the Are we even looking at the same circuit? I see only one transistor.Yuh got me there. It was the same circuit but I misremembered how it was drawn. |
Re: Foldback Simulation
Thank you Helmut
Could you,pls,let me know the procedure step by step to obtain the output foldback function for the circuit of your exemple?I understand I have to run the .asc file but i don't know which steps are necessary after the temporal simulation Thank you Best regards Vittorio |
Question: any built-in function that returns the type of analysis being run?
Hi. I've got a quick question. I've looked on this site and scad3.pdf but haven't found anything... could be it's just hard to pick the right keywords.
Is there any built-in function that I can use to determine the type of analysis being run, for example, .tran, .ac, etc.? I've run into a problem where one of my "B" type current sources works fine in .tran analysis, but does not seem to incorporate a correct response in AC analysis. I've found some messages related to this (but I still don't fully understand the limitations involved). In any case, I can solve my problem by using different methods to calculate separate circuit output voltages for .tran and .ac analyses. But this relies on users to understand and choose which output to use. My experience is that people often ignore even written warnings about model usage. So I'd like to create an "if" type function that yields different answers depending on whether the analysis type is AC or not. Anyone have suggestions? Thanks. |
Re: Discrepency with Cadence
--- In LTspice@..., "Shah" <shah_m_sharif@...> wrote:
Hello Shah, No SPICE program can calculate AD,AS,PD,PS. You have to enter these values, if you want take them into account. Even Cadence can't calculate that. If it does, it's because you have entered data about these sizes in another place in the design suite. Still my question. Why L=1.2um in a 45nm process? Best regards, Helmut
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Re: LT1016,
Kerry
The Book chapter written by Jim Williams who I think wrote the application note you suggested put the chapter together from such application notes but the book is quite recent while the application note is quite old. however a lot of he info is indeed in the free application note. Somewhere on the web is a paper comparing op amps with comparators and is good reading . high speed comparators of 10ns and less rise time need proper consideration to hardware layout. Regards Malcolm |
Re: Discrepency with Cadence
Helmut,
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After swapping the source and drain ( source is close to the gate) I am still getting similar AC current. If you have simulated this circuit is it possible to upload it? Anohter slightly seperate quesiton, does LTspice auto calculate AD,AS,PD,PS from the width and lenght and the mosfet model file or do I need to put values for AD,AS,PD,PS for more accurate AC current at high frequency? Thanks, Shah --- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
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Re: How to find Qpoint of an MOSFET in LT spice
John Woodgate
In message <k2dmni+hnbn@...>, dated Fri, 7 Sep 2012, tonyatritecom <tony@...> writes:
You will normally get some help when you demonstrate you have made at least some effort towards solving your problem, even though many strongly disapprove in principle with students seeking help here with homework.I think that it's OK to ask for *help*, but not to expect someone to provide complete answers. If I answer a homework enquiry, I try to guide the enquirer into the right thinking pattern towards the solution, often by asking questions in return, like, 'What does the data sheet say about the maximum supply voltage?' -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk The longer it takes to make a point, the more obtuse it proves to be. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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