I am using an SSM2604 at 64 kHz with a 12.288 MHz MCLK. When outputting signals above fs/4 I see increasing imaging products. At 20 kHz the output waveform looks like linearly interpolated discrete points. The data sheet shows a DAC digital filter frequency response that has around 60dB attenuation for signals above 0.55fs. I assumed this meant that images would be attenuated by the amount indicated.
Am I doing something wrong? Is the DAC digital filter just linearly interpolating between values instead of interpolating in a bandwidth limited fashion? Is a separate antialaising filter required? Or does the DAC digital filter just apply to noise & not images?
The is little information available about this part in either the data sheet or else where on the web site.
It appears there are different DAC digital filter shapes depending on the oversampling ratio (MCLK/FS). At 192x it doesn't look anything like the data sheet graph, but at 256x or 384x it does.
But there isn't any mention of this in the data sheet...
I apologize for the delay. We will respond as soon as possible. Thanks for your patience.
I have more or less answered this myself. The filter response curve
shown in the data sheet is only valid for x256 & x384 oversampling
rates. At x192 (where I was using it) it has a completely different
response (that isn't very good).
Stanford Research Systems
1290-D Reamwood Ave
Sunnyvale, CA 94089