Hi folks, I've spent a little over a year on the above platform (modifying BOTH the 'HC711 and DSP programs, putting my own menus into the LCD and getting the DSP to accept serial port commands through the MCU via SPI) and while I've gotten quite proficient in "fighting through" the sometimes perplexing lack of documentation on some of its features, there's STILL a few areas I can't figure out! My current problem is, every time I feed an analog sine wave into EITHER the on-board ADC or an external AKM (24-bit) unit via the fiber interface, I get annoying aliasing or "birdies" - the first "zero beat" I get is usually around 2800 hertz. If it were a faint artifact I might be able to live with it, but it's LOUD and actually interferes with my ability to take real measurements. What's even more perplexing is, I incorporated a "bypass" mode for either the left or right channel (sort of like the way it comes) and the aliasing is present even on the channel that's NOT being processed - it WILL go away if I "patch around" the board and just feed the AKM ADC fiber output into an AKM DAC fiber input so it's not in EITHER ADC! Could this be an artifact of some jitter or decode glitch in the clocks generated by the Lattice part or perhaps the DSP itself? Or would it be related to a problem in the (ill-documented) I/O timing? I realize this PCB is a little "developer-obscure", does anyone have any experience tracking down the source of this problem on OTHER platforms? I'm totally clueless on this one...thanks in advance for trying! Jeff Lawton WaveLinear |