Is it possible to generate frequency ramp using AD9912?
The AD9912 does not have frequency ramp capability. You could check out the following parts instead:
1. AD9910 - 1GSPS 14-bit DAC, same clock input and DAC resolution as AD9912
2. AD9913 - 250MSPS 10-bit DAC
3. AD9958 - 500MSPS, 10-bit DAC, 2 Channels
4. AD9959 - 500MSPS, 10-bit DAC 4 Channels
As Mark points out, the AD9912 does not have a dedicated digital frequency ramp generator.
However, if the required ramp update rate for your application is relatively low, you could implement a sweep manually via the SPI port. That is, by writing a linear sequence of frequency tuning words to the device at regular intervals (the ramp update rate).