PLL frequency synthesizer for TDMA systems

This paper describes a PLL frequency synthesizer with the high-speed frequency switching for TDMA systems. To achieve the high-speed frequency switching, we have proposed a novel synthesizer of a fractional-N phase locked loop employing a direct variable counter with a multi-modulus prescaler, which can be operated at a higher reference frequency. Additionally to reduce spurious outputs, loop filters are switched from a high-speed loop to a low-speed loop after a constant time. An 800 MHz band PLL frequency synthesizer using these schemes has a frequency switching time of 1.4 ms and a spurious output suppression ratio of -78 dBc at a 50 kHz offset frequency