Phase lock loop system with ultrafast lock times for half duplex time division multiple access wireless data applications

Abstract

A method of providing low energy consumption ultrafast lock time in a mobile communication system normally operating at slower lock times and requiring occasional ultrafast lock times when switching from the transmit mode to the receive mode and/or from the receive mode to the transmit mode. There are provided a normally operating PLL and a normally disabled DDS. Responsive to a requirement for the ultrafast lock time, the DDS is enabled and substituted for the PLL. Subsequently, responsive to removal of the requirement for the ultrafast lock time, the PLL is substituted for the DDS and the DDS is disabled. When the transmit and/or receive mode requires a frequency above the capability of the DDS, a mixer is added for mixing the output of the DDS with a signal having stable reference frequency to obtain a frequency equal to the sum of frequencies of the DDS output and the stable reference signal. As a further embodiment, when the DDS is enabled and substituted for the PLL, the operating frequency of the PLL is altered and when stabilized at the new operating frequency, the PLL is substituted for the DDS with the DDS being disabled. There is also provided a rapidly stabilized change in frequency of a signal wherein a DDS provides an output at a known frequency with the output of the DDS being mixed with the signal from the source of stable signal of predetermined frequency to obtain a frequency equal to the sum of the frequencies of the DDS output and the stable reference signal higher than the maximum capability of the DDS.