| 摘要 |
A voltage controlled oscillator is capable of rectilinearly changing an oscillation frequency over a wide range while keeping, to a fixed value, a signal amplitude of a ring oscillator using an differential amplifier by eliminating dependency of the signal amplitude upon a tail current. A load resistor section of each delay element is constructed of a variable resistor element for changing a differential output current flowing corresponding to variations in tail current, and a clamp circuit for fixing the amplitude of an output terminal of the delay element. A control voltage for changing the current of the former part is generated by the replica circuit of the delay element that is equivalent to an arrangement that the part, for fixing the amplitude of the output terminal of the delay element, of the load resistor of the delay element, is removed, and by a control circuit for equalizing a reference voltage for determining the amplitude of the output terminal of the delay element to an output voltage of the replica circuit.
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