Applications of Motorola microcontrollers in the design of general purpose frequency synthesizers

The design of a general-purpose frequency synthesizer that synthesizes frequencies in the band of 100 Hz to 150 kHz, is accomplished using fractional phase-locked loop techniques. The method utilizes a 68HC11 microprocessor to generate very stable reference frequencies. A software program has been written to vary the reference frequency over the desired operating range. Operations at higher frequencies provided better phase noise performance due to the design constraints of the low pass filter. At 150-kHz carrier, a sideband response up to 50 dB attenuation was measured. The frequency synthesizer has been simulated using the TUTSIM software program. A settling time of as low as 50 ms for the loop lockup was observed