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Altera_Forum
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8 years ago

Driving Ladder DAC

Hi, Im trying to drive a resistor ladder DAC from my DE-1 SOC board, despite of my DAC being very accurate im getting somewhat shotty results. The setup is relatively simple driving the resis...
Altera_Forum's avatar
Altera_Forum
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8 years ago

The first image is what I would expect to see; each bar is about twice the height of the previous bar.

The other two images appear to have an added bias (ie, base value) compared to the first image.

If as you say the resistor values are 300-600-1200-2400-4800-9600-19200-38400-76800 (like the baud rates...) then if the passive pullup were enabled, typically about 25K, it would really start to affect the values above 9600 rather dramatically, enabling a 25K pullup to H, when your resistor is pulling to L, forming a voltage divider.

Just my suspicion based on your waveforms.