Hi folks, my first time posting here!
I need some advice on a circuit that's misbehaving.
I am trying to make a DDS function generator on a Terasic DE0-Nano board. The digital stuff I believe is acting well.
I am generating a sine wave, triangular wave and a square wave. The square wave is driven by a SN74LVC2G04, and is completely separate from the DAC.
I've limited the frequencies to max. of 2 MHz.
The board itself is just a single layer, milled PCB with some of the bigger components on the other side.
Problems lie in my own DAC board (that's using the AD9760ARZ). I needed to use an "I-V" converter to create my output signal, and I used one directly from the AD9760 datasheet, and stuck a Sallen-Key filter at the end.
However, above 1.5 MHz - for the sine wave - strange things start to happen. I start getting really bad distortions on my wave.
For the triangular wave, things look bad even earlier, at about 1 MHz.
Note: the connection between R3 and pin 2 of AD8041 has been bodged, because apparently reading datasheets is hard.
Any ideas what might be going on?