Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)

#89935

? ?"I don't know what the "uni-polar" means"

?It means one polarity.

Andy

Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)

#89934

Hi, Andy:

I had fixed the value (time, amplitude) of DC sweep source (.TRAN) to lower speed, smaller scale.

And I found in a very small range, it has exp behavior, but output a DC bias about 4.2V.

Is it possible to plot the curve similiar to the datasheet ? in the datasheet it says these equations:

"VLOGOUT = (0.5V)LOG (I1/I2)"

"VO3 = K (0.5V)LOG (I1/I2), K = 1 + R2/R1"

And says the log amp is utilized to measure the physical quantities which has exponential characteristic (varies large.)

I don't know how to show this characteristic in the waveplot of LTspice.

I don't know what the "uni-polar" means, if you meant that it shouldn't have the negative value, I had fixed it ,it came from this ,at the beginning I used the negative value because I couldn't show the curve, so I simply thought maybe I could enlarge the scale of the waveplot to see what's different.

The equation's simple to understand, but it's hard to plot the curve of "Vout vs. I1/I2". I don't why, and not sure whether it's caused by the model mismatch or other reasons.

Thank you for the reply

Best regards.

Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)

#89933

I re-ran it as a DC sweep, keeping I1 sufficiently positive.

I get pretty good agreement with the datasheet's plot, noting the polarity inversion of your circuit, up to about 4 or 5 mA.? At that point, the core log circuit runs out of steam and clips.? That is higher than the specified input dynamic range (3.5mA max), so I think it is good -- even though the ratio I1/Iref is not as high as it is shown on the datasheet plot.? Obviously, they used a smaller value for Iref in that part of the datasheet plot.

This is the first time I simulated (or even used) a log amp so I'm not an expert.

Andy

Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)

#89932

Since it is a log amp, shouldn't the input current (I1, I2) be uni-polar?

Andy

?

Re: Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)

#89931

ericsson.sunshine?asked about a Log amp from T.I.

This is just a very first impression, and may or may not be meaningful.

You are doing this as a transient analysis. ?It's possible you are sweeping the input current too fast.? At some signal levels, and depending on external components, the part's bandwidth can be as low as 1 Hz or less, so the step response could be quite slow, maybe too slow for a 10ms step.

Did you try a .DC sweep analysis?

Over some of the range, I think it is oscillating.

All the negative values in the X-axis should be discarded, to correspond to the datasheet's plots. ?(Now, why are there negative values at all, I wonder?)

Regards,

Andy

Problem of plotting (TI) log112 curve (Vo vs. I1/I2) (log112 model in file folder)

#89930

Hi, :

Here is a pure technical problem.

I had found a log amp model (TI) LOG112 at the file folder.

When I was trying to plot the "Vo vs I1/I2" curve mentioned in the datasheet, I can't work it out. The plot is unexpected.

I had uploaded the example file at?

20160801_log amp (TI) log112.zip

Thank you for any opinion

Simplicity brings fun & satisfaction.

Re: Looking for a IDT74CBTLV3253 model.

#89929

Gunoiar?wrote:

? ?"Also, I observe that the logic library contains only the graphical description on certain ?devices but lacks the simulation definitions."

I am confused what you mean by that.

Are you talking about the logic parts in the [Digital] section of the library?? They all have actual models already.? What's missing are the parameters that MAY need to be set, to get realistic performance.

I am not aware of logic parts in the LTspice library that are graphical symbols only.

Some analog parts, e.g., MESFETs, SCRs, IGBTs, valves/tubes, and varistors, are symbols only and you must provide the model.

Regards,

Andy

Re: Looking for a IDT74CBTLV3253 model.

#89928

Hello,

You could use the basic AND, NAND from the folder [Digital] plus a NMOS and PMOS transistor. See the circuit diagram in the datasheet.?

?

I recommend to make a hierarchical schematic. This means you make top-level schematic with your circuit and a lower level schematic with the IDT74CBTLV3253.

Best regards,

Helmut

Looking for a IDT74CBTLV3253 model.

[email protected]

#89926

Hello one and all.
it's time to bite the bullet. Do some digital simulation on an analog simulator :)

I need to design a four channel sequential track and hold. Part of this contains a 2 bit digital counter stirring 4 switches. it appears the the ?? IDT74CBTLV3253? integrates these functions well.

Does any one have a model for it? please include an example how to use it.

Also, I observe that the logic library contains only the graphical description on certain? devices but lacks the simulation definitions. Is that meaning that I have to develop an entire library?

Sincerely
G.

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Re: Ferrite Beads

#89927

Dear Andy,

the Standard Ferrite Bead symbol in LTspice of Wurth is not encrypted.
Once you selected a particular P/N and right click on the symbol,
you can see the datas used for the simulation model.
And can also edit them- if needed.

The current dependent Ferrite bead Ferrite Bead (I)? model of Wurth is encrypted.

Re: Google groups

#89925

Indeed, fine LTspice group, I am, most times, happiest to take the advice that one "learns more with mouth closed" ;-)

Thanks to all of you who proffer your experience in both LTspice and electronics, generally!

I try to find my way, using available web resources and the many thread topics to be found in the archives, thus do not, often, need to ask too basic a question ....

Vielen Dank, Helmut, especially, but also many thanks to the "usual suspects"

Barry Rowland
Bayern (that's near Germany ;-) )