Choose a variable gain amplifier for hall effect sensor output

Hi, 

I am looking into this. I will check for what you might be able to use and get back to you. 

Thanks, 

Kris

Hello, 

I apologize for getting back to you late. I will need more information regarding your application to provide you with a device you can use. 

Would you be able to share the sensor that you are using? Is the output of the sensor sitting on a common-mode voltage? Do you plan on using the variable gain amplifier to correct the nonlinearity, or do you just want to amplify the sensor output so that it fits the 0-5V range? Any more details about the application will help also.

We do have programmable gain in amps that provide adjustable gain. If you would answer the questions above, I will be better able to suggest a suitable part. 

Thanks, 

Kris

Hi Kris,

Thanks for getting back to me. The hall effect sensor I am using is A1389 from Allegro. It's output is 2.5V when there is no magnet flux around it. I mounted this hall effect sensor at the back of the shaft of a voice coil actuator (VCA), and since the shaft of the VCA is ferromagnetic, the magnet flux sensed by the hall effect sensor changes when the shaft moves. Therefore I could get the position of the VCA to do feedback control. 

The raw output of the sensor is about 2.5-2.9V as I measured using a multimeter, and the output is also nonlinear with respect to the position of the shaft, as I calibrated using a laser displacement sensor. Therefore, I want to amplify the raw output so that it lies between 0-5V for me to read using a microcontroller. 

So my goal is to amplify that signal at least, and if possible also try linearizing it using a variable gain amplifier. I have tried AD605, however I had trouble using it because it has some output common mode voltage, which I don't think is what I want.

So now my plan is to use AD620 with a digital potentiometer AD8402. In this case, I can use microcontroller to control the resistance of AD8402, which will change the gain of AD620.

Do you think my current plan is a good choice? And feel free to suggest any other solutions that you think are better.

Thanks,

Hank

Hi Hank,

Based on the frequency of operation you can  filter-out the DC offset and then use a Potentiometer to attenuated the signal and linearize it. Then use a fixed gain Amplifier to get the range of signal between 0-5V.

Regards,

Koushik

Hi Koushik,

Thank you for your answer. 

But could you please explain in more detail about "use a Potentiometer to attenuated the signal and linearize it"? I am not sure how to use a potentiometer to attenuate and linearize the signal.

Hi Hank, 

Thanks for the information you provided. Couple more things:

I am interested to know the transfer function of your sensor. How non-linear is the measurement and how much correction is needed?

Would it be an option for you to just digitize the signal first and linearize the signal in the digital domain?

Thanks, 

Kris

Hello again Hank, 

One more option for you -- are you set on using a Hall effect sensor? You could also use an AMR sensor for your application. The ADA4571 has an integrated sensor and conditioning circuit and is suitable for position sensing. I highly recommend you check out the reference design which interfaces the ADA4571 with the AD7866. The documentation includes data for linear position measurements and should have everything you need to implement the solution.

Thanks, 

Kris