A 4.3 GHz BiCMOS VCO with multiple 360° variable phase outputs using the vector sum method

A 4.3 GHz voltage controlled oscillator (VCO) with multiple independently tunable phase outputs is presented. The VCO is realized by coupling two LC oscillators together in order to obtain quadrature signals and is tunable between 4.12 and 4.74 GHz. The variable phase outputs are achieved by varying the amplitudes of the in-phase and quadrature signals independently and then combining these signals together. By using multiple Gilbert cells as variable gain amplifiers (VGAs), multiple tunable phase outputs are achieved with the use of only one quadrature VCO. The VGAs are controlled using a custom non-linear digital-toanalog converter. The entire circuit is designed using a 3.3 V SiGe BiCMOS process. A maximum phase noise of -108.17 dBc/Hz was measured over the entire tuning range at a 1 MHz offset. The outputs of the VCO can be used as local oscillators that achieve phase shifting during radio frequency up or down conversion.Armscor S. A. Ltd and the Business Unit: Defence, Peace, Safety and Security (DPSS), Council for Scientific and Industrial Research (CSIR), South Africa.http://www.springerlink.com/content/0925-1030ai201