/diy/ - Do It Yourself

Can I produce frequency modulation by connecting the clock of a direct digital synthesis chip to a voltage controlled oscillator or does the clock need to be stable? I've googled it but I can't find any examples of someone doing that.

I need a function generator with analog frequency modulation. There used to be chips like the ICL8038 that could do that easily but they're all discontinued. With DDS chips a microcontroller writes some registers to change their frequency which means I'd need a fairly fast MCU and ADC to get the analog modulation throughput I want. If I used a VCO like the CD4046 as the DDS clock I could use a super cheap MCU that doesn't even have an ADC.