Hi Chitharanjan_M ,

If you could move your post on these forums (11) High-Speed DACs - EngineerZone (analog.com) and (11) High-Speed ADCs - EngineerZone (analog.com), someone there should be able to suggest to you the ADC and DAC that will meet your requirements.

Regards,

JC

OK JCCillion,

Updated the same in that forum.

Thanks & Regards,

Chitharanjan M

There may be a conflict in the requirement for 125MSps (x 16-bits) versus galvanically isolated 4-20mA loop. That's a lot of bandwidth, especially considering the expectation to run it through SPI. Usually, interfaces requiring >1GHz bandwidth can only be chip-to-chip LVDS, getting those kind of high-bandwidth signals off-board with signal integrity is quite expensive. Look into using JESD204B instead of 4-20mA loop. If the 4-20mA loop is in an industrial setting, there will be issues with radiated EMI as well as received EMI vulnerability. For such a high sample rate, it's best to keep the loop area minimal.

Would it be possible in your application to place your DSP right next to the 125MSps ADC/DAC, where the signals are acquired and used? Then use lower-bandwidth, galvanically-isolated SPI or 4-20mA interface to report the decisions made by the DSP.

AD9683 might be a good choice of ADC meeting >125Msps (170Msps), 14-bit resolution, high-speed JESD204B interface. But it looks not easy to galvanically isolate JESD204B.

There are parametric search tables available for all of our product lines:

Parametric search table for 4-20mA Input A/D Converters:

https://www.analog.com/en/parametricsearch/12823

The AD74115 is specifically designed for 4-20mA loops, and it does have an evaluation kit; however, it's a SD ADC so I'm not sure it would meet your high-speed requirements. We have Isolated A/D Converters up to only 21Msps.

Parametric search table for 4-20mA Current Loop D/A Converters:

https://www.analog.com/en/parametricsearch/11040

Digital Isolation Technology:

https://www.analog.com/en/parametricsearch/11444#/

High-speed ADC (>10Msps):

https://www.analog.com/en/parametricsearch/10826

Unknown said:

We have Isolated A/D Converters up to only 21Msps

Is this Supports 4-20mA input?

Unknown said:

Would it be possible in your application to place your DSP right next to the 125MSps ADC/DAC, where the signals are acquired and used? Then use lower-bandwidth, galvanically-isolated SPI or 4-20mA interface to report the decisions made by the DSP.

125Msps and 4-20mA input is the special requirement from our customer, we can't do any compromise in that. We are ok with ADC which doesn't support integrated isolation, but we need ADC analog inputs should be galvanically isolated, so do you have any ADC front end circuit which is galvanically isolated?

Unknown said:

AD9683 might be a good choice of ADC meeting >125Msps (170Msps), 14-bit resolution, high-speed JESD204B interface. But it looks not easy to galvanically isolate JESD204B.

Please share me the galvanically isolated analog front end circuit which is suitable for AD9683

Unknown said:

High-speed ADC (>10Msps):

The DACs under these category supports 4-20mA current input? Because in non of the ADC datasheet under this category not mentioned about the 4-20mA analog input

Unknown said:

Parametric search table for 4-20mA Input A/D Converters:

Looks here mentioned about 4-20mA analog input. Which means high speed ADC >10MSPS not supports 4-20mA current input?

For an example of a galvanically isolated 4-20mA system, refer to AD74115 datasheet figure 58 "AD74115 and ADP1034 System Level Diagram."  Note that the galvanic isolation barrier is bridged by the ADP1034 digital isolator. The analog input is not galvanically isolated from the 4-20mA system being measured; the entire analog front-end is galvanically isolated from the microcontroller on the digital side.

This is a typical approach to galvanic isolation systems. These isolation systems have limited bandwidth due to the physics of how the isolation barrier is crossed while maintaining the required dielectric breakdown characteristics. This causes signal distortion. Digital signals can be designed with enough noise immunity to successfully cross the isolation barrier without distortion; analog signals cannot. For this reason, galvanically isolated measurement systems are best designed to place the analog to digital converter close to the sensor being measured, and then bridge the isolation barrier with a suitable digital isolation product.

AD75115 is a 16-bit sigma-delta converter; its maximum output data rate is many orders of magnitude slower than your stated requirement.