Patent ID: 6856204
Filing Date: 2005-02-15
Classification: H03L

Abstract:
1. A phase locked loop (PLL) circuit having a wide locked range, the PLL circuit comprising: a phase/frequency detector for detecting a phase difference between an external input signal and an output signal of the PLL circuit; a charge pump for increasing or decreasing an output voltage level in response to the output signal of the phase/frequency detector; a loop filter for removing a high frequency element from the output voltage of the charge pump; a voltage controlled oscillation unit for outputting a signal having a predetermined frequency as an output signal of the PLL circuit in response to the output voltage of the loop filter; and a voltage controlled oscillator (VCO) range shift unit for decreasing a sensitivity of the output signal of the PLL circuit to the output voltage of the loop filter by increasing or decreasing an internal current of the voltage controlled oscillation unit in response to the output voltage of the loop filter, the VCO range shift unit including: a node connected to the voltage controlled oscillation unit for receiving and outputting an output current of the VCO range shift unit; a first current source connected to a power supply voltage; a first switch connected between the first current source and the node; a second current source connected to the ground voltage; a second switch connected between the node and the second current source; a first comparison unit receiving the output voltage of the loop filter and a first reference voltage for turning on the first switch by outputting a high voltage level when the output voltage of the loop filter is lower than the first reference voltage and turning off the first switch according to an opposite state, and having a hysteresis characteristic; and a second comparison unit receiving the output voltage of the loop filter and a second reference voltage for turning on the second switch by outputting a high voltage level when the output voltage of the loop filter is higher than the second reference voltage and turning off the second switch according to an opposite state, and having a hysteresis characteristic, wherein the first reference voltage level is lower than the second reference voltage level and the first and second switches are turned off when the output voltage of the loop filter is higher than the first reference voltage and lower than the second reference voltage.