Oscillation frequency control circuit
First Claim
1. An oscillation frequency control circuit comprising:
- a voltage-controlled oscillator;
a frequency divider configured to divide an output from the voltage-controlled oscillator;
a phase comparator configured to compare phases of an external reference signal and an output from the frequency divider;
a loop filter configured to smooth out an output from the phase comparator and output a control voltage to the voltage-controlled oscillator;
a detection circuit capable of detecting the external reference signal;
a pulse generation circuit configured to generate pulses upon receipt of a pulse generation information to be output to the loop filter;
a memory capable of storing therein a control voltage information and the pulse generation information corresponding to the control voltage information wherein a value of the control voltage output from the voltage-controlled oscillator used as the control voltage information;
a switch configured to turn on/off a connection between the phase comparator and the loop filter; and
a control unit configured to turn on the switch when a level of the external reference signal detected by the detection circuit is within an appropriate range while turning off the switch when the level is outside the appropriate range to thereby output the pulse generation information stored in the memory to the pulse generation circuit,wherein the pulse generation circuit is a pulse width modulation circuit, and the pulse generation information output from the control unit is information on a pulse width modulation duty cycle.
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Accused Products
Abstract
Provided is an oscillation frequency control circuit, which corrects its own frequency so that it can hold an oscillation frequency stably even when it does not have an input of a highly stable reference signal but makes a self-run. The oscillation frequency control circuit comprises a voltage-controlled oscillator, a frequency divider, a phase comparator, a loop filter, a detecting circuit for detecting an external reference signal, a PWM circuit for generating pulses, when pulse generating information inputs, to output the pulses to the loop filter, a memory for storing the pulse generating information corresponding to voltage information, a switch for turning ON/OFF the connection between the phase comparator and the loop filter, and a CPU for turning ON the switch, if the level of the external reference signal detected by the detecting circuit is within a proper range, but OFF the switch, if the level is outside of the proper range, thereby to output the pulse generating information stored in the memory, to the PWM circuit.
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Citations
7 Claims
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1. An oscillation frequency control circuit comprising:
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a voltage-controlled oscillator; a frequency divider configured to divide an output from the voltage-controlled oscillator; a phase comparator configured to compare phases of an external reference signal and an output from the frequency divider; a loop filter configured to smooth out an output from the phase comparator and output a control voltage to the voltage-controlled oscillator; a detection circuit capable of detecting the external reference signal; a pulse generation circuit configured to generate pulses upon receipt of a pulse generation information to be output to the loop filter; a memory capable of storing therein a control voltage information and the pulse generation information corresponding to the control voltage information wherein a value of the control voltage output from the voltage-controlled oscillator used as the control voltage information; a switch configured to turn on/off a connection between the phase comparator and the loop filter; and a control unit configured to turn on the switch when a level of the external reference signal detected by the detection circuit is within an appropriate range while turning off the switch when the level is outside the appropriate range to thereby output the pulse generation information stored in the memory to the pulse generation circuit, wherein the pulse generation circuit is a pulse width modulation circuit, and the pulse generation information output from the control unit is information on a pulse width modulation duty cycle. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification