| 摘要 |
<p>A voltage controlled oscillator includes an oscillator (30) having at least one first capacitor (47, 49). The oscillator (30) receives first and second input voltages and charges the first capacitor with a first current corresponding to the first input voltage. The oscillator (30) oscillates at a frequency corresponding to the first and second input voltages. To remove the adverse influence on the oscillating frequency by the change of process parameters caused in the stage of manufacturing the voltage controlled oscillators, a second capacitor (36) is charged for a predetermined period by a current corresponding to the first voltage. After the charging of the second capacitor (36) ends, a sample/hold circuit (37) samples and holds the charged voltage across the second capacitor (36). An operational amplifier (31) receives, at its positive input terminal, the output voltage of the sample/hold circuit (37), and, at its negative input terminal, the reference voltage. The operational amplifier (31) controls the first voltage so that the output signal of the sample/hold circuit (37) will be equal to the reference voltage. Repeating the sequence of the charging, sampling and comparing operations eliminates the influence upon the oscillating frequency by the change of the process parameters caused in the manufacturing stage.</p> |
