Systems for portable, radio-based, digital communication often employ three basic modules, an IF (intermediate frequency) module, an RF (radio frequency) module, and a baseband processing module. Generally, the components used within each module and/or the modules themselves originate from different vendors. Inherently, then, differences exist among the modules, including operation regulated by differing clock frequencies. Unfortunately, accommodating these varying frequencies often is cumbersome and costly.
A simple approach to providing the different clocks results in the use of separate oscillators within the device. As shown in FIG. 1, crystal 1 would provide the clock signal for a baseband module 10, crystal 2 would provide the clock signal for an IF module 12, and crystal 3 would provide the clock signal for an RF module 14. However, the size, weight, and power consumption of the device increases with the addition of the separate oscillators, which hinders the intended portable nature of the device. Further, cost increases with each additional component, as well as susceptibility to variability among the components with the production of numerous devices.
Another approach incorporates flip-flops and combinational logic within the baseband module 10 to allow division of a single clock into the necessary clock frequencies for the remaining modules. However, this latter approach is limited to division by integer values. Thus, for systems having modules whose required frequencies vary by non-integer values, e.g., by a factor of 2.5, successful operation relies on the use of multiple oscillators. As mentioned above, incorporation of multiple components is not efficient.
Accordingly, a need exists for generation of non-integer divisions of a single clock to meet operational requirements in a cost-effective and successful manner.