current source associated with the first charge pump cp 1 is set to 0 9 the resulting filter can have the frequencies f 1 f 2 as if it had the capacitor c 1 the capacitance value of which is reduced by a factor of ten it is therefore possible to reduce the capacitance value of the capacitor c 1 to a similar capacitance value to the capacitor c 2 in a transmission pll contained in a high frequency ic intended by the inventors for application since c 2 has several hundred picofarads c 1 can be reduced as well to approximately several hundred picofarads then since capacitors having capacitance values as low as the foregoing can be sufficiently formed on a semiconductor chip the loop filter can be integrated on the semiconductor chip further since this embodiment eliminates the need for the buffer which would be required in the loop filter of fig4 that controls the switches in phase it is possible to prevent noise generated in the buffer from introducing into the output vout to increase a phase error of the pll loop moreover the elimination of the buffer can result in a corresponding reduction in the circuit size next other embodiments of the loop filter according to the present invention will be described with reference to fig7 and 8 these embodiments permit the pll to rapidly pull in upon start of a voltage controlled oscillator vco to enable a high speed lockup operation a phase comparator designated by pd compares.