DSP cycloneII dev. kit : how to remove dac transformer ?

[Altera_Forum]

I'm trying to get some low frequency signals from DAC converter. 

It's not possible because of T1 transformer cutoff frequency What is the frequency - bandpass ? Why this transformer ? How to remove it ? Anybody can help me ?  thanks.

[Altera_Forum]

Yes, you must desolder T1 and place a jumper/wire from T1.3 to T1.6 to get a single ended DC coupled output from the DAC.

[Altera_Forum]

Thank you for the reply.  

Unfortunately, a wire between T1.6 and T1.3 produces only a positive signal to the output.  If I want to get negative signals, it is necessary to use an amplifier OP680, with +5V/-5V supply power, 4 additional resistances (500ohms) :(    Unfortunately, even on terrasic adc/dac daughter card, there are transformers on the DAC outputs.  Do you know a card without this transformer?   thank you in advance, ssiami 

[Altera_Forum]

You didn't specify additional requirements for signal output, but you can add a negative offset current to the single ended output to create a bipolar signal. Of course an output amplifier provides more options.  

 I'm not aware of suitable DC capable high speed AD/DA board, you may want to design your own hardware according to your needs.

[Altera_Forum]

I desolded T1 and place a wire from T1.3 to T1.6. I have now sinus signals from 1Hz to 1MHz with a very good S/N ratio.  

Thank you!

[Altera_Forum]

hello,  

Now, I try to desolder transformers on ADC side.   The schematic is not the same as for the ADA terrasic daughter card. The IC is ADS5500.  can you give me the schematic and procedure?  why there are two transformers T3 and T2? thanks   (http://www.alteraforum.com/forum/editpost.php?do=editpost&p=21033)

[Altera_Forum]

I found a schematic on ADS5500 datasheet with THS4503 amplifier. 

What do you think about that ?

[Altera_Forum]

I was just busy to suggest a similar solution. 

 The schematic has been provided by Altera in the DSP-Kit support package. See the ADC page in attachment.  The ADC needs a DC biased, and at best differential signal, see the respective TI datasheet for reference. Thus unlike with the DAC output, it's not sufficient to remove the transformers to get a DC capable input. A differential amplifier would be the usual solution, reference schematics are given in the ADC datasheet. For reduced performance requirements, the input signal can be supplied single ended, but the inputs must be still biased at V_CM (1.65V).  P.S.: A negative supply voltage is needed for amplifier. But it must not necessarily be -5V, -1.5 or -2 V are sufficient to provide the required common mode range.