Granted Patent B2

US 7,911,285 · App. 12/391,941 · Granted Mar 22, 2011

Abstract

Claims (12)

1. A reference frequency control circuit comprising:

a frequency voltage converting circuit configured to receive an oscillation signal from an oscillator circuit including a crystal oscillator or a ceramic oscillator, and output an output voltage corresponding to a frequency of the oscillation signal, the oscillator circuit being a circuit configured to oscillate at a frequency corresponding to a level of an input signal; and

a control circuit configured to control a level of the input signal so that the output voltage is at a predetermined level,

the oscillator circuit including a variable capacitance circuit having a capacitance corresponding to a level of the input signal, the oscillator circuit configured to output the oscillation signal having a frequency corresponding to the capacitance,

the control circuit including an error amplifier circuit configured to output an error voltage as the input signal to the variable capacitance circuit, the error voltage having a level corresponding to an error between the output voltage and a reference voltage having the predetermined level, and

the error amplifier circuit changing a level of the error voltage so that the output voltags at the predetermined level.

2. The reference frequency control circuit oscillator of claim 1 , wherein the variable capacitance circuit includes a varactor.

3. A reference frequency generating circuit comprising:

an oscillator circuit including a crystal or a ceramic resonator and a variable capacitance circuit having a capacitance corresponding to a level of an input signal, the oscillator circuit configured to output an oscillation signal having a frequency corresponding to the capacitance;

a frequency voltage converting circuit configured to receive the oscillation signal from the oscillator circuit, and output an output voltage corresponding to the frequency of the oscillation signal; and

an error amplifier circuit configured to output an error voltage as the input signal to the variable capacitance circuit, the error voltage having a level corresponding to an error between the output voltage and a reference voltage having a predetermined level, the error amplifier circuit changing a level of the input signal so that the output voltage is at the predetermined level.

4. The reference frequency generating circuit of claim 3 , wherein the variable capacitance circuit includes a varactor.

Assignments (9)