Abstract: Provided is an LC resonance voltage-controlled oscillator (VCO) used for a multi-band multi-mode wireless transceiver. In order to generate a multi-band frequency, a capacitor bank and a switchable inductor are included in the LC resonance voltage-controlled oscillator. The LC resonance voltage-controlled oscillator employs an adjustable emitter-degeneration negative resistance cell in place of tail current sources in order to compensate for non-uniform oscillation amplitude caused by the capacitor bank and prevent the degradation of a phase noise due to the tail current sources.

Abstract: A differential voltage controlled oscillator (VCO) employed in a frequency synthesizer used as a local oscillator of a wireless communication on-chip transmitter/receiver is provided. More particularly, a differential current negative feedback VCO equipped with a current-current negative feedback circuit that suppresses low- and high-frequency noise is provided. A differential current negative feedback VCO includes a resonator determining oscillation frequency, and an oscillator generating negative resistance. In the oscillator of the differential current negative feedback VCO, transistors Q1 and Q2 form a cross-coupled pair, and negative resistance is generated by positive feedback of the cross-coupled pair. And, transistors Q1 and Q3 together with an emitter resistor and a capacitor form a current negative feedback part, and transistors Q2 and Q4 together with an emitter resistor and a capacitor form another current negative feedback part which is disposed opposite to a resonator.

Abstract: A wide-band multimode frequency synthesizer using a Phase Locked Loop (PLL) is provided. The multiband frequency synthesizer includes a multimode prescaler, a phase detector/a charge pump, a swallow type frequency divider, and a switching bank LC tuning voltage-controlled oscillator having wide-band and low phase noise characteristics. The multimode prescaler operates in five modes and divides a signal up to 12 GHz. The wide-band frequency synthesizer can be used in various fields such as WLAN/HYPERLAN/DSRC/UWB systems that operate in the frequency range from 2 GHz to 9 GHz.

Abstract: Provided is a voltage-controlled oscillator (VCO) using a current feedback network for use in a wireless communication terminal. The voltage-controlled oscillator has high input impedance and low output impedance, so that a degree of isolation from the external load is excellent, thereby preventing degradation of the Q-factor by the load in overall oscillation circuit. In the voltage-controlled oscillator of the present invention, an LC resonator is provided to generate positive feedback, and negative resistance may be obtained at a wider frequency range by tuning a varactor of the LC resonator. And a boosting inductor is inserted into the positive feedback loop to have a greater negative resistance, therefore it is possible to prevent a problem in which the oscillation does not occur due to the parasitic resistance components generated during circuit fabrication.