A novel low phase-noise differential Colpitts VCO by using transformer feedback technology is presented in this paper. This work demonstrates a simple differential topology with dual-transformer approach to reduce phase-noise at low DC power consumption. A symmetrical circuit layout can be realized easily by transformers and a commonly cross-coupled structure is not adopted herein because cross couple feedback path is also a serious parasitic effect more at 10 GHz operation. Therefore, dual-transformers provide a compact feedback path and DC feed path simultaneously. Consuming a DC power of 8 mW in the VCO core, the circuit exhibits a phase-noise of - 115 dBc/Hz at offset frequency of 1-MHz and the figure of merit value is - 184.1 dBc. (c) 2007 Elsevier Ltd. All rights reserved.