FREQUENCY ADJUSTMENT CIRCUIT

PURPOSE:To realize the frequency adjustment circuit which can shorten the lock up time. CONSTITUTION:The voltage waveform appearing in both ends of a resistance element R1 of an LPF6 is subjected to voltage/current conversion by a voltage- current converter VIC, and the electric charge is stored in a capacitor C3, and the voltage generated in the capacitor C3 as the result is inputted to comparators CMP1 and CMP2; and when the generated voltage is in a certain level or higher, switching elements SW1 and SW2 are turned on, and the electric charge proportional to the quantity of electric charge passing the element R1 is allowed to flow to a capacitor C2 in the same direction as flow to the capacitor C3 through the element R1 and is stored. Thus, a boost circuit 7 is operated to quickly switch the unlock state to the lock state only when the unlock state in which the pulse (electric charge) outputted from a phase comparator 5 is large is set.