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I remember only a little. I was simulating a simple non-inverting amplifier used in a DC setting as a refresher and I noticed that depending on which model OpAmp I used, I got very different simulator results. The LM and LF data sheets. I am using this summary as a refresher as to what all these terms mean.
So I don't think this affects the simulation, but I'm not sure. This is the circuit I'm testing. It's attempting to amplify the Vin voltage by 1. The specification is there to tell you that there is some range of input voltages that you can expect the op-amp to function correctly. You have to check the datasheet to see how the common mode voltage range changes with supply voltage. For example, take the LF In figures 4 and 5 it shows the common mode voltage as a function of positive and negative supply voltages referenced against the average supply voltage.
Looking at figure 5 of the LF's datasheet, the minimum common mode voltage allowed for a -6V negative supply is about This aside, for whatever reason Partsim's model for the LF is broken most likely the pins are out of order. Luckily, you can get the model file here. Note that it needs a bit of tweaking to get it to work with partsim. Interestingly the output doesn't quite line up with theory; that's because I simply assumed that because figure 5 of the datasheet doesn't show the negative supply voltage vs.
Instead, it is simply unspecified. The model just happens to work below that, though I don't know which behavior you'll actually get in real life. The standard Boyle opamp macromodel that is used for most old opamps does not model the common mode input range. However, temperature performance, common-mode input range , offset voltage, offset current, input protection, power supply rejection, noise, THD, input impedance, good ac output resistance, and change in supply current versus supply voltage are a few of the more important parameters that are not modelled with the Boyle macro topology.
Things get more interesting for LF For the bog standard one, you also get only a Boyle model indetified as "LFC" inside the file. Downloader beware. Of course I have no idea what partsim uses. The saying "show me the code" translates into "show me the model" when it comes to opamp SPICE simulations beyond the very basics.
That's not how it's gonna work, because of the non-inverting configuration, the factor is going to be 2. But leaving that aside, even with TI's LM model you at least get it to limit output below the 12V rail And here's how it works; you'll want to refer to the Boyle schematic while reading the stuff below. I've circled the parts that simulate the rail-related limits for the output.
For LM, the voltage sources in series with the diodes that simulate the rail limits, this is the right-most are set to. So on the low side it goes to 0 after the diode drop is subtracted, but the high side goes to about So both sides high an low limited to about 1.
This is how they simulate that LM is capable of single supply operation, but LF isn't. I have to see now what the fancier LFNS model buys here, if anything. Well, no real difference.
I think I figured out what the addition is in the NS model. LF incl. That means for a 5V common mode voltage a change in the output of 50uV. With the NS model we get exactly that "common mode effect". There is however not simulation of the common-mode input range in the latter either, it seems.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Simulation difference between two similar OpAmps Ask Question. Asked 4 years, 6 months ago. Active 4 years, 6 months ago. Viewed times. I was comparing the two datasheets and I don't see a significant difference. Here is the simulation using the LM Fizz Huckle Huckle 1 1 gold badge 8 8 silver badges 15 15 bronze badges. If you use 0 V for the negative supply, it for sure won't work with an input common mode voltage below 4 V, and maybe won't work at all, since there's no specs for that situation.
The Test Conditions cell is empty, but then every cell to the right is split. I don't see it defined in the data sheet anywhere. Vs is however the balanced supply voltage in the LF datasheet.
Now you know why. Active Oldest Votes. There's no way the output will go smoothly from 0 to 12V. They must be using some kind of ideal op-amp model here, not anything like a real op-amp. Luckily, TI also has spice models for the LM Now to more practical matters. First you say: It's attempting to amplify the Vin voltage by 1. Fizz Fizz From the plots above, it looks like an ideal op-amp model, not anything trying to model reality.
Stay tuned for some updates. My resistor ratio is 1. I am also well aware of the inability to get right to the power supply voltage I stated that in the question. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
Datasheet LF412CN - National Semiconductor IC, OP AMP, DUAL JFET, DIP8, 412