Hello,
I'm a new user, and I would like to use a AOP THS4551. After download PSpice for TI, I can draw the electronic assembly (see in this attached the picture) but when I'm trying to simulate, It's impossible. Do you know what is stopping me from doing the simulation ?
Thank you for your helps.
Regards
Hi Kai,
Thank you now I have something but I need to know the variation of the output voltage as a function of the input voltage.
But I have only this curve :
Probably I didn't choose the right parameter (see the red circled)?
Hello,
Next to the red area you selected in your screenshot, you can see the simulation profile 'Schematic1 - ac sweep'. You'll want to switch to a time domain profile or create a new simulation profile. An AC frequency analysis will not provide voltage output as a function of voltage input.
When you create a simulation profile, you can choose what type of analysis to perform. I am guessing you want to do a transient analysis as the input voltage varies over time; you can then plot the output voltage with a voltage probe. For 1000Hz sine wave, I recommend a time domain simulation run-time of 1ms. After you run the simulation, you can edit the X-axis variable (by double-clicking on the x-axis) to be the input voltage (V1) rather than Time, and now you can view a plot of the output voltage as a function of the input voltage.
You can use a second probe on the other side of R4 to see how the FDA output behaves according to the input.
Please see the following images and let me know if you were intending to accomplish something else:
Best,
Alec
Hi Alec,
Thank you for your helps, I'm a new user you say :
'You'll want to switch to a time domain profile or create a new simulation profile.'
Yes but I have only one choice 'SCHEMATIC-ac_sweep' in my scrow bar, probably when I create a new simulation profile I must choose in time domain. I will see how to do it, if you have any information how to do it i am interested
My goal is to know the max gain, because I've a very small signal comes from a hydrophone about : 0.1µV and 1.78 mV. So I wonder if I need 2 AOPs instead of just one ?
After downloading your version, I've just I changed some settings. I run the simulation and something is wrong, the gain of my amp is 1 but the output voltage is lower than input voltage. Please see in this attached.
Thank
Regards
Yann
Hello Yann,
Thank you for sharing more about your application. Could you elaborate on your input source and amplifier needs?
Regarding capacitive sensors, please examine the following links for ideas and resources:
The following two TI articles discuss working with piezoelectric sensors:
https://www.ti.com/lit/an/slyt369/slyt369.pdf
https://www.ti.com/lit/an/sloa033a/sloa033a.pdf
For the signal you are observing in your simulation:
Best,
Alec
Hi Alec,
In fact with the generator I can simulate a 1 mV voltage :
And after I can have Vs=f(Ve) with my specification but I don't know why I have a negative output offset about -6mV.
Probably, it's not very important because I am in differential mode ?
Thank
Regards.
Yann DO
Hi Alec,
According to the assembly of the circuit in the datasheet below :
It's normal that I vary the resistance to seek the maximum gain (without distortion). But it's not the same resistor normally we do it with R5 (RF1) and R1 (RG1) and not with R3 and R2 like your answer earlier. And the second point is the output voltage of AOP is inverted with respect to the input signal. Because we're in an inverting amplifier.
After reflection, it was necessary to invert the probe at the output to have the right signal.
I was able to simulate with a 5.62µV input signal (which corresponds to my low level of the hydrophone) see this picture below :
I can see a little offset about 40mV, probably I must use a capacitor to remove the offset ? What's do you think about this solution ?
Thank for your helps.
Regards.
Yann DO
Hello Alec,
I read the first link and the last link that you gave me, apparently it's not that simple! Yes I use this AOP (THS4551) with a ADC (ADS127L11), this is my purpose to amplify the signal coming from the Hydrophone.
After DS (DataSheet) on page 73.
I need to amplifie the signal in differential mode and I'm not sure if my AOP in inverter is in differential mode. Give me some time to read all the information you gave me but I'm not sure to find the solution to eliminate the 40mV offset.
Thank you for your patient.
Regards
Yann DO
If you have a more complete/full circuit you can share (with the ADC perhaps), I would appreciate the extra information. If you are mainly simulating and designing the FDA portion, I can investigate typical circuitry for your application.
Hello Alec,
Thank you for your helps, yes my goal being to use this FDA (AOP THS4551) with the ADC (ADS127L11) because I am going to order these materials and I would like them to correspond to our specifications. I have meetings and trips, I'll come back to you next week with the new elements (I will do my best).
I just looked at the ADC library and apparently we don't have the ADS127L11 component in the library to do the simulation. Which I think there is no choice but to work only with AOP-THS4551.
Regards,
Yann DO
Hello Yann,
I have some follow-up points:
1. What is the output impedance of the hydrophone sensor? Could you operate the circuit with 10 Ohm gain resistors and 14.04 kOhm feedback resistors? If your sensor is okay with a low input impedance at the FDA, you would only have a 25mV offset instead of 40mV. Please provide details regarding the sensor you are using and its impedance profile. See the following images:
Fig1: Vout across load resistor w/ 25mV offset
Fig2: Schematic w/ smaller resistor values
2. This behavior shown above (the difference of 15mV of offset) is due to the input bias current offset caused by large resistors. As stated in the Planet Analog articles I linked in a prior answer, the output offset due to bias current is strongly affected by large resistors, such as the 1404kOhm (~1.4 MOhm) feedback resistor.
3. Earlier you mentioned adding capacitors to the circuit; I was unsure what you intended to accomplish with these capacitors. Were you thinking of AC-coupling the ouput of the FDA? If you only need the AC signal and do not require the DC signal, this would be a good choice to minimize the DC offset voltage you are experiencing. The issue will be choosing the right value capacitor, as you are operating at low frequencies correct?
4. Finally, you may prefer to use the THS4531 or THS4531A, which is very similar in performance to the THS4551, but has a much lower maximum bandwidth. As you are operating in a low-frequency range, this choice might benefit your design cost.
Best,
Alec
