I am looking for information and hints for the design of a Direct Digital Synthesizer that should generate a narrow-band FM signal from a reference frequency and numerical parameters.
Not to design it to the circuit level myself, but to get some hints about what kind of block diagram to use, maybe some hints for suitable chip types (like "AD9911"), and articles that discuss methods to obtain a spectrally clean signal.
The synthesizer should to the following:
- use a 10 MHz reference
- generate an output frequency of about 430 MHz (fixed, but settable)
- put NBFM voice modulation on the signal (3 kHz deviation) based on an available stream of 16-bit signed audio samples (12000 samples/s)
- the generated output frequency should be closely predictable from the parameters and the supplied modulation information, i.e. when two of these units are operating independently with the same parameters and modulation, they should generate the same signal frequency. (carrier phase is not important)
- spurious output suitable for use in a transmitter, after analog bandpass filtering.
Any hints for a DDS/NCO chip that can take multi-bit modulation instead of the typical 2/4/16 level FSK?