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Altera_Forum
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16 years ago

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

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...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

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.