TINA/Spice/ina333: cross verification of the Simulation result of two stage cascaded INA333 and suggestion in order to get desired ac signal

Hi Vasanth,

It looks like your INA333 TINA file did not get attached to your original inquiry. Please try attaching and sending it again. Be sure to use the "Insert File" (paperclip icon in the toolbar) to insert the file.

The INA333 simulation model does model the amplifier's noise. Filtering will reduce the total noise that would normally appear at the output by limiting the bandwidth. You would have to let us know what level of noise and bandwidth your INA333 application requires before we could could comment about the need for filtering.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi thomas,

thank you  for your reply. now i sent the circuit. Please find the attached file .I did simulation in TINA of my requirement by cascading two INA333 of input AC voltage magnitude=130uV Frequency = 50Hz
Desired output after two stages =1.3V with no noise desired.

one INA33 is 1k gain another is 10 gain we took in order to get interms volts. 1.Please verify the circuit and simulation of the attached file. 2. please check the output noise level and suggest whether filter is required or not in order to get the original signal

Otherwise you suggest right thing for the above needed.

ti.rar

Hi Vasanth,

I am attaching the schematic you posted on the other thread to consolidate this discussion. There are a few issues here:

1) You are likely going to run into issues placing a 100nF capacitor on the output of the INA333. This is not the proper way to filter the signal. 

2) R3 and R6 in your schematic are shorted out to ground, so functionally they do not serve a purpose.

3) If you don't have a differential signal and are grounding the non-inverting inputs of each device, why are you using an instrumentation amplifier? You would be much better off using a single stage with a wider bandwidth op-amp in a filter configuration. 

4) No matter what you use, there is going to be some noise in your system. If you establish what amount of noise you can tolerate (a target SNR for example), then we can point you in the direction of an op-amp configuration that will meet your requirements.

HI,
Thank you for suggestion , if you mind , will you do Reconstruct my circuit for below needed specification
input AC voltage magnitude=130uV Frequency = 50Hz
Desired output after two stages =1.3V with neglisible noise desired
i wanted like structure of INA , filter after that one ADC please suggest the thing
1.Please verify and modify the circuit and simulation

Vasanth,

I'm sorry but this is not enough information to provide a circuit recommendation. First, I need to understand what you are interfacing with and why you want to use an instrumentation amplifier. If you truly do need to use an instrumentation amplifier, then I'd like to understand why you chose the INA333. A device such as the INA828 would be lower noise, and has sufficient bandwidth for you to only need a single stage. What constitutes negligible noise is very subjective. I can add filtering but if I don't know what you are targeting It's difficult for me to make the right recommendation.

You mentioned that you are trying to get this signal into an ADC. Have you selected the ADC yet? If you have, what is its SNR at your desired operating point? If you have not, what kind of resolution and sampling rates are you looking for? Depending on the converter, the INA itself may not be capable of adequately driving it and you may need to include a buffer amplifier before the ADC.