ADC12QJ1600EVM: Question on Using FDA for DC-Coupled Input with ADC12QJ1600EVM

Md Shariful Islam

Part Number: ADC12QJ1600EVM
Other Parts Discussed in Thread: LMH5401, THS4541, ADC12QJ1600

Hi,

I am considering using a fully differential amplifier (FDA) to convert a single-ended input into a differential signal so that I can interface directly with the ADC EVM. I am looking at two options: the THS4541 (with its evaluation board) and the LMH5401 high-speed amplifier.

I previously attempted to capture data using a single-ended input after modifying the ADC EVM as suggested in the forum. However, I am observing overrange on that channel (Channel A) and am unable to retrieve data through the FPGA. In contrast, I am able to capture AC-coupled signals correctly on the other channels (i.e., Channel B).

According to the ADC EVM documentation, DC-coupled differential input is supported, provided that a fully differential amplifier is used to set the common-mode voltage to 1.1 V. Given this, I wanted to confirm whether using either of these FDAs would be appropriate for my setup. Both seem to meet the bandwidth requirements of my signal.

Best regards,
Shariful

3 months ago

0 Bill Clarke 3 months ago

TI__Intellectual 1290 points

Either of these FDA devices are capable of driving the ADC12QJ1600, but take care to ensure the FDA is biased for enough headroom to drive the output common mode and support the ADC's full-scale range.

0 Md Shariful Islam 3 months ago in reply to Bill Clarke

Prodigy 30 points

Hi Bill, Thanks for your answer. I have another question. If I remove the DC offset from my signal by DC blocking and feed the signal directly to the ADC's AC-coupled input option, is that okay? Since I have no issue with AC signals, I can capture them perfectly.

Thanks in advance.

0 Bill Clarke 3 months ago in reply to Md Shariful Islam

TI__Intellectual 1290 points

You can certainly AC couple - in this case you may consider using a balun to achieve better dynamic range & noise than an FDA. You can see our EVM design as a reference.

+1 Md Shariful Islam 3 months ago in reply to Bill Clarke

Prodigy 30 points

Hi Bill, Thanks again. In the EVM schematic, the balun is already there. If it works, then I don't need to think about the FDA or any more things.

Data converters

Data converters forum

ADC12QJ1600EVM: Question on Using FDA for DC-Coupled Input with ADC12QJ1600EVM