A quadrature oscillator for LTE/LTE-A standards with an improved quadrature-mode stability

This paper introduces a quadrature oscillator for LTE/LTE-A standards with an improved quadrature mode stability using transformers. In Inductor-based (L-based) quadrature voltage controlled oscillators (QVCO), there exist two stable quadrature modes. When a transformer is used in place of an inductor in a QVCO, it is shown that the selected quadrature mode of oscillation is different from and more stable than the L-based QVCO. This additional stability ensures that only one mode of oscillation in T-based QVCOs is selected whereas in L-based QVCOs, cascode transistors are commonly used for this purpose. This is demonstrated using an oscillator designed in a commercially available 130 nm CMOS process. The oscillator provides a tuning range of 40.6% (2620-3033, 3423-4446 MHz), a phase noise of -112 dBc/Hz at an offset of 2.5 MHz from 3033 MHz, and a maximum power consumption of 26.4 mW from a 1.2 V supply.