Multibit PLLs achieve improved efficiency and performance: better utilization of the frequency spectrum, to serve more users at a higher quality of service (QoS), reduced RF transmit power, and reduced power consumption in cellular phones and other wireless devices.
Phase noise, spurious emission, and jitter are results of the above phenomena.
In CDMA, frequency hopping achieves better performance than phase coding.
The performance envelope of a PLL defines the interrelation between the above essential criteria of performance - for example improving the frequency resolution will result in a slower PLL and higher phase noise, etc.
PLL design is an interdisciplinary task, difficult even for experts in PLLs.
Improved performance is possible by using the faster bits of the counters, taking into account the additional available information.
This effect is only relevant in multibit PLLs; for Unibit PLL, there is only the one-bit signal MSB, therefore no overflow is possible.
The additional degree of freedom in Multibit PLLs allows to adapt each PLL to specific requirements.
Early multibit PLLs used a microprocessor, a microcontroller or DSP to close the loop in a smart implementation.
Improving the PLL performance can make better use of the frequency spectrum and reduce transmit power.