7.3.15 FSK Modulation
Direct digital FSK modulation is supported in LMX2572. FSK modulation is achieved by changing the output frequency by changing the N divider value. The LMX2572 supports two different types of FSK operation.
- FSK SPI mode. This mode supports discrete 2-, 4- and 8-level FSK modulation. There are eight dedicated registers used to pre-store the desired FSK frequency deviations. Program FSK_SPI_DEV_SEL to select one of the FSK deviations at a time.
- FSK SPI FAST mode. In this mode, instead of selecting one of the pre-stored FSK deviations, change the FSK deviation directly by writing to FSK_SPI_FAST_DEV. As a result, this mode supports arbitrary-level FSK, which is useful to construct pulse-shaping or analog-FM modulation.