Description

To improve the phase noise, various experiments are done to modify the coupling networks. The coupling technique presented is applicable to N differential Colpitts QVCOs for multiphase signals generation. The QVCO is combined of two similar current-switching differential Colpitts VCOs in which the first core VCO is connected to the second in an in-phase manner, and the second core VCO is connected to the first in an anti-phase manner. For this connection the substrates of the interconnected transistors as well as the substrates of MOS varactors are used. In all the above proposed Colpitts QVCOs extra devices are used for coupling, which can degrade the overall performance of the QVCO and increase the chip area. Furthermore, any mismatches between coupling devices may disturb the symmetry of the circuit, leading to phase error. This work presents a new low-phase noise low-power quadrature voltage-controlled oscillator in which two identical current-switching differential Colpitts VCOs are coupled without extra coupling devices that could potentially degrade the phase noise and power consumption. A Ka band QVCO fabricated in CMOS 0.18 πm technology was designed to verify the effectiveness of the proposed QVCO structure. The measurement results reveal that the quadrature output signals of QVCO have about °1:52dBm output powers with less than 1dB amplitude imbalance and less than 6±phase diÆerence in the frequency range of 31.9 to 32.7GHz.