THS4552RTWEVM: Simulating THS4552

Hi Uday,

I am attaching some references you could look into to answer your questions. Most of these will require some form of simulation so it would be easier to get this information that way. Regarding the simulation itself, I added some videos you can reference on how to simulate on Pspice for TI. We also have TINA-TI which I have found easier to setup and run but Pspice has a lot more reference material online. As far as the download, this should download a program onto your PC which you should be able to use offline. This is not a program that is accessed through an online site.

Below are two app notes that discuss FDAs in detail which would be great references to read through.

"Differential Op Amp Single-Supply Design Techniques"

Using Single-Supply Fully Differential Amplifiers With Negative Input Voltages to Drive ADCs

The next two links are video series. The first link covers FDAs and discusses some of the ideas that are mentioned in the two app notes above. The second is a video series on how to run PSpice for TI.

Precision labs series: Fully differential amplifiers | TI.com

Explore PSpice® for TI design and simulation tool | TI.com

Best Regards,

Ignacio

Hi Ignacio,

Thanks for the response and apologies for late revert. 

I'll go through the material and update. 

But I did not get how to get pspice installation. Is it possible to share the software via sharedrive or something?

Thanks

Uday 

Hi Uday,

Once you submit your information you should get approved and I believe you are sent to a different page to download. There is no share drive for this software. Were you able to submit your information? If you did so and did not get any information whether you were approved, I would try submitting again.

Best Regards,

Ignacio

Hi,

I did submit the details and I got link to download. From that link only 8MB is getting downloaded.

Hi Uday,

I believe that was the .exe file to setup the download. From there you should click the file then input your email that your TI account is attached to and copy and paste the access key that was provided in the approval email you received. This will then start downloading the software from the web onto your computer.

Best Regards,

Ignacio

Hi Ignacio,

I'll try downloading that way and update.

I have gone through couple of videos. They are really informative. Thanks.

Can you elaborate on the topic where common mode dc offset of signal driving half and non driving half differ? Can you share any reference how to deal this situation and any example circuit?

Thanks 

Uday

Hi Uday,

Can you direct me to which video or section you are referring to. I am not sure I understand your question.

Best Regards,

Ignacio

Hi Ignacio,

In the following link , video 2 , "Input, output, common-mode and differential-swing", timeline is 6:40."

Notice that only one half of the FDA is driven by a signal source, while the other non-driven side is connected to ground. The signal driven half of the FDA should have the same Common Mode DC offset as the nondriven side. Otherwise, the FDA will amplify the difference in Common Modes as a differential output offset voltage. In instances where the signal-driven side has a common mode other than ground, the non-driven side should be driven by a low-output impedance, wideband DC source. A common solution to this problem is to use an op amp whose bandwidth is similar to that of the FDA being driven.

Can you give me any example or reference for this concept?

Thanks
Uday

Hi Uday,

I am attaching two screenshots of simulations that highlight the idea mentioned in the video. As you can see if one branch has a certain DC voltage while the other does not, an FDA will gain this DC difference at the input as a differential offset voltage at the output. Hope this helps.

Best Regards,

Ignacio

Hi Ignacio,

Thanks for the results. Can you please share these simulation files?

Also video discusses the methods to take care these offset difference lby using wide bandwidth op-amp etc. Can you please elaborate and share any references on this?

Hi Uday,

I am attaching the file I used. As for the method mentioned, the reason we want to use an op amp is because ideally the output impedance is relatively low which is what you would want from an ideal voltage source. However, across bandwidth it changes and rises as it reaches the bandwidth limit of the amplifier. You therefore want an amplifier that has the same bandwidth as the FDA so it can keep that node at X volts by maintaining a low impedance output.

Best Regards,

Ignacio

 FDAOffset.TSC 

Hi Ignacio,

What other parameters I need to consider while choosing the op-amp.

For Eg in my circuit, there is BIAS voltgae. As I understand this should be given via op-amp. Can you suggest any device here?

Thanks,
Uday

Hi Uday,

This will depend on your design parameters such as voltage supplies available. I would consider a device such as the OPA355. This device should have enough bandwidth to support this FDA and is rail to rail out which makes it easier to work with. It is also unity gain stable so you can use it as a buffer for your voltage reference. I went ahead and attached the product page below. 

OPA355 data sheet, product information and support | TI.com

Best Regards,

Ignacio