Terasic ADA Daughter Card

For DAC channel A, you can remove T5 and add a zero ohm jumper for R60. You get a 50 ohms DC coupled single ended output.

An AD8132 or AD8138 could be used in a circuit according to the AD9248 datasheet. But there's neither a suitable place on the board nor a differential connector option to place it external to the board. So it must be glued to the board. It's possible to my opinion, but I don't want to suggest it generally.

Ok, I understand the DAC end. Thanks

As for the ADC end, I think I have to try to do it. So where on the board is the best place to put in the signal? At R4 (for ch. A)??

I am assuming that the signal should be at Vin+. Is this correct?

And you say that this signal need to have a 1.5V bias?? I think it should be possible to use an op amp but I it is also quite simple for me to add a 1.5V DC bias to my signal. Do you think this would work?? Have I misunderstood?

Thanks again for your invaluable help.

I suggest to read the ADC datasheet regarding suggested options for DC input signals. I mentioned a true differential driver, which is the best option in terms of supressing common mode interferences and also achieves best ADC linearity.

A single ended configuration would e.g. remove R1, C1 and T2, connect left side of R5 to VNCT_A and left side of R4 to input jack. The input voltage range is 0.5 to 2.5 then.

Hi,

I have decided to opt for the using a differential amplifer for the ADC input but am unsure about how to attach it to the board due to it's small size. Would you advide using the evaluation board? (EVAL-ADDIFFAMP)??

http://www.analog.com/en/amplifiers-and-comparators/operational-amplifiers-op-amps/eval-addiffamp/products/product.html

It appears to have SMA input/output. In this case I can just connect it to the board and make the adjustments to get single ended configuration to prevent the DC blocking from the capacitor and transformer? Does this sound feasible??

Thanks

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I suggest to read the ADC datasheet regarding suggested options for DC input signals. I mentioned a true differential driver, which is the best option in terms of supressing common mode interferences and also achieves best ADC linearity.

A single ended configuration would e.g. remove R1, C1 and T2, connect left side of R5 to VNCT_A and left side of R4 to input jack. The input voltage range is 0.5 to 2.5 then.

--- Quote End ---

Thanks for the info. I tried to implement this single ended configuration but was unsure of a few aspects. I removed R1 C1 and T2 and connected R4 to the input jack so that now the SMA input is connected the VINpA pin of the AD9248 by only the 33ohm resistor R4. I assume this to be correct

The problem is where to connect R5 to VINCT. To the pad of the removed transformer T2 or directly to the bridge between R2 and R3?? Also, by left side I assume you mean left side on the schematic, i.e input jack side as opposed to ADC side.

I hope I can get this working as the DAC side works perfectly. Unfortunately there is very little useful info on the AD9248 or terasic board data sheets about configuring for single ended ADC operation

Thanks

Ben.

Hi,

I desolded the DAC transformer on a EP2C70dsp card and I have now frequency from 1mHz to 1MHz.

I am interested in buying one terrasic ada daughter card.

Before, I would like to see the schematic.

Where can I find this shematic ?

Thanks

It is in the support archive, downloadable from Terasic thdb_ada_cd_v1.2.zip

I'll append it for your convenience.

thank you,

Do ou know the R60 and R61 values ?

why these resistances ?

They doesn't exist in altera dsp kit.

Yes, I can confirm that the R60 and R61 resistor positions are empty on the Terasic ADA board, at least with the CIII starter kit. Putting a 0ohm resistor on R60 ane removing the transformer does indeed give you single ended (DC- coupled) operation at the DAC with very little impact in terms of additional noise.

However, if you require also a single ended input, please note it is much more complicated to achieve this at the ADC end and I have not yet been able to do it.