TI,
ADA4528-1 offers better specifications than OPA333. Any comments ?
Regards,
JayantD
Jayant,
One potential issue you should be aware of, because your application is in a noisy industrial environment, is that opamps rectify electromagnetic interference (EMI) at their inputs and it appears on the outputs as an offset voltage. Below is an oscilloscope screenshot I took in our lab here, it shows the change in offset that occurs in a competitor's unprotected bipolar opamp when a 40MHz sine wave is applied to the input:
Channel 1 (yellow) is the input sine wave and channel 2 (blue) is the output voltage of the amplifier. The amplifier was configured as a buffer for this test but it is important to remember that this offset will scale with gain. The testing methodology and relevant design equations are described in application note SBOA128. The OPA333 has input EMI filtering to prevent this effect in noisy environments. The EMI rejection ratio of the OPA333 is shown below:
The ADA4528 datasheet makes no mention of input RFI or EMI protection so I'm unable to do a comparison at this time. However, if the device is not protected against EMI outside of its bandwidth, you may find it exhibits a greater-than-expected offset voltage in an industrial environment.
Jayant,
There are a few benefits to the internal EMI filter over an external RC filter.The main benefit to the customer is that we test the performance of the IC with the integrated filter to ensure its resistance to EMI over a wide frequency range (currently 10MHz to 6GHz). All passive components suffer from non-idealities (parasitic capacitances and inductances) which limit the ability of a filter to suppress noise at very high frequencies. Unless you are using passive components for RF/Microwave applications, the effectiveness of an RC lowpass filter will be severely limited above ~100MHz. This is an effect that ALL filters suffer from, shown below is the insertion loss plot from the TPD2F702, a dedicated EMI filtering part:
Notice that above 200MHz the ability of the part to filter out unwanted signals is being reduced due to parasitic elements in the filter. Unless a filtering solution is tested, there is no guarantee that it will effectively remove out-of-band noise. Second, on-chip passive components can be very closely matched so the corner frequency of the filters on both inputs will be very close. This is important because any mismatch in the filters on the opamp's inputs (due to component tolerances) can allow EMI applied to the opamp as a common-mode to become a differential signal and pass through the device. Lastly, because the filter is integrated internally, there are benefits in cost and board area.
