Patent ID: 6411660
Filing Date: 2002-06-25
Classification: H03J,H03L,H04B

Abstract:
A device for reducing a lock-up time in a time division duplexing system, the system having a first frequency synthesizer for generating a reference frequency, a receiver having a first mixer for mixing the reference frequency with an input frequency to generate a first intermediate frequency and a second mixer to generate a second intermediate frequency, and a transmitter having a third mixer to generate a transmission frequency, the device comprising:a band switching controller for receiving an inverse channel selection signal and generating a corresponding band switching controller voltage; and a second frequency synthesizer for generating third and fourth intermediate frequencies to the second and third mixers, respectively, according to a channel selection signal for setting transmission and reception modes, said second frequency synthesizer including: a voltage controlled oscillator for generating a frequency according to either of a charge pump voltage or the band switching controller voltage applied at an input of the oscillator; a loop filter for shaping the charge pump voltage being applied to the input of the voltage controlled oscillator; and a phase locked loop for comparing the reference frequency with a frequency output from the voltage controlled oscillator to generate a voltage according to a phase difference therebetween to the input of the voltage controlled oscillator via the loop filter, wherein the band switching controller voltage maintains an input voltage level of the voltage controlled oscillator upon receiving the inverse channel selection signal when switching from the transmitting to the reception mode.