Patent ID: 8344770
Filing Date: 2013-01-01
Classification: H03L

Abstract:
1. A PLL circuit comprising: a first divider that divides a reference frequency; a voltage controlled-temperature compensated crystal oscillator that is a crystal oscillator to compensate for temperatures and makes an oscillatory frequency variable in accordance with a first control voltage; a first control signal generator that receives the reference frequency and an output from the voltage controlled-temperature compensated crystal oscillator as input, performs a lock operation, and outputs an alarm signal that is a first value in a lock state and is a second value when input of the reference frequency is lost or in an unlock state, while outputting the first control voltage to the voltage controlled-temperature compensated crystal oscillator; a second divider that frequency-divides the output from the voltage controlled-temperature compensated crystal oscillator; a selector that selects an output of the first divider when the alarm signal is the first value and selects an output of the second divider when the alarm signal is the second value; a voltage controlled crystal oscillator that makes an oscillatory frequency variable in accordance with a second control voltage; and a second control signal generator that receives an output of the selector and an output of the voltage controlled crystal oscillator, performs a lock operation, and outputs the second control voltage to the voltage controlled crystal oscillator.