Sharp Kabushiki Kaisha Corporation

Yusuke Kishino

Shinji Amano

A voltage-controlled oscillator includes (i) a first variable-capacity element, (ii) a resonance circuit whose resonance frequency changes in accordance with a control voltage applied to the first variable-capacity element, (iii) a second variable-capacity element connected in parallel with the first variable-capacity element, (iv) resonance frequency range switching means which switches the variation range of the resonance frequency of the resonance circuit by switching the capacity of the second variable-capacity element, and (v) a resonance frequency correction circuit which corrects the resonance frequency in such a manner as to prevent the ratio between resonance frequencies before and after the switching of the variation range from depending on the control voltage.

Voltage-controlled oscillator, transmitter, and receiver

An FM signal receiver for use in receiving a burst signals as in a Bluetooth system includes a BPF and a frequency-demodulation circuit, each having, for example, a phase shifter, which is constructed from similar or related circuitry so as to enable adjustment of the frequency characteristics of the BPF and frequency-demodulation circuit through an identical control signal. A short-circuit switch is disposed linking the input and output terminals of an amplifier. A control circuit opens the switch in a receiving operation and closes the switch in an adjusting operation. Thus, adjustment is carried out without using the amplifier. Therefore, an amplifier offset does not affect the frequency-to-voltage conversion by the frequency-demodulation circuit in the adjusting of the frequency-demodulation circuit and similar adjusting of the BPF. Thus, the BPF is prevented from being incorrectly adjusted due to the offset. The BPF characteristics are suitably adjusted.

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Kashiba, Japan

Yusuke Kishino